r‘ '9
A!’           >ARJQ -DEDES SA IRRlGATjON_PROj[ECT
FEASIBILITY STUDY REPORT
CONTENTS OF TH E REPORT
SERIAL
NO
1
2
3
VOLUME NO.
PARTICULARS
EXECUTIVE SUMMARY
MAIN REPORT
Part i - Repeat
Pvt il - Maps i Drawings.
ANNEXURES
VOLUME -1                   SURVEY AND INVETIGATJON (ANNEXURES -1 to 31 4                  volume • l ta>                Topograpur $jrue> GocmorptwiogKai Studies 4
Geological Geowchntai inweangausn
Part ii - Report
s                  volume -1 (bj 6                VOLUME ’ll
Pan ii - Appendices
NATURAL  RESOURCES  [ANNEXURES  -  4  to  S) Forestry Energy 4. Caicnmem Development Plan
VOLUME - III                 WATER RESOURCES {ANNEXURES -7 to 11)
7                Volume - III \a,i              Meteorological i Hyorqlogscai A riyorogeologicai Studies Dam 1 Appurtenant Wonts
e volume I IE (b)
9
Pan 1 - Report
Pari It - Drawings
--_
\ 5*<E
Z?<'
L
imgatfin & Dramaje
rtf
x
10
volume - III (C)
Part 4 - Report
JJ
X
11
Part II - Drawings
HvdraMJjc Structures
Parti--Repcn
Part 11 - Drawngi
\o\
\
Z' C
12               Volume - III (d> 13
rKfll *
VOLUME IV                   AGRICUTLRUE (ANNEXURES - 12 to Tip
=r'
14                Volume - IV (a)              Soil Survey & Lana Evaluation
15                     volume - IV (b)              Agricultural Planning
16               Volume • IV ^c)             Livewx*.   Fisheries   Agricultural   Metnsn^non   6
Agncultural Mattering
VOLUME-V
ENVIRONMENTAL AND SOCIO - ECONOMIC ASPECTS
I ANNEXURES -19 lo 25)
17
Volume - * (a)
Environment, Health & Socio-economic Aspects
IS
Volume - v (b)
Organhzatton S Management, Physical Infrastructure
RMMtofflem. Financial & Econ&mc AnalysisArjff BtdrSSa TJTigiUoa Project
0™ Appurtenant Warks
TABLE OF CONTENTS
TaBLF Oft CONTENTS
LJSTOFTABtl.
LEST Of FIGURE
rNTRODLXTJOX ...
1 1 GENERAL
1.2 Background A Revsew of Previous Studies.. / 2,l-;,' Ehjffl-
/ 2 2 jStLn SaoncMi
? J J Daw Zousil-jfi'LiH The in mOT
11 a ■ u 111 ki 1111
. IV
hl.l I MHHBIU I ■ 111
i iii»ii1111»wi1aii
mi. m.iaim
... .JS
.I ..._ ..1
J
J
J
1J Tfc Present D.am Site______
III!
Illi
!■>
Ill     mini
z ■GEOLOGY
2.2 Dam Site
77 J
2.2 J HtfAty FlOT cnrf jftrwF flrrf J 2 J Thf W.ijgW             Hf
1111 ■ .ii 111 n 11111 rw 11 n-mi 11 ii
lii
JJ
uni rniiimmn
....... W
,_„„n
2 4 Geoldqou Structures J.             DaM FOUNDATION ..
3 1 General
3
Fopi DwFoumoOOn
J 2 i' Es-tf-ffwirfiGw /tap*- Cot 5r.ptf.tfur
iuimi Miami ami
■ Il ii.. ma.i
> ii.ii.bjiiiil .i. ii.. i1111biiiii? " i im i ii liii i nrmi-—in -mini
2 2 2 /jcln-nflnra
3.2 J JfatanOTiiM frumwir
.'lAtJ'i1 ZjW
3.3 Grouting Requirements.
J.J.4 Cunai«t Ghawinj ...._____________ 4   DONSTKUCTION MATERIALS ....
4 1 BGMQWAMaK FOft CUT.._«.
l-fc
IS
IS
Ji J7
... IB
20
.20
■ ■II
< J 2 C-Ari* <j v i I'l'flyr
4O
< J 4 ATvito
4. J. 3 ONsj* jfjnej
. 24
1111 in 1111 ui 1111 i 11 ixuj 11 iu u 11 uj m..
4.2 Borrow Areas for Rock Fcl Shell Material ..
4ZJAD5W pored
<2.7 Gw Ar jI neo
4.3 CKjarry Sites for Rock Rip Rap ................... 4.4 CkiARftr &te foft Coarse Aggregate ....
4.5 Sand
....
zz __ .23
_____.23
26
76
24
Zfl
2S
29
....30
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A4OTX1O1
mm—i■ ii run■ in■ ■ ■■>
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JO
4 5 2 PfaliN-ay i
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nder. _.................
....
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4 fl J
iii ■ kuaniHi mi
4 tf 4 DL¥4*4fW
...
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uni mi.. i
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■4 fl J <Vai/j/rOTr-w G^nGy wirwd^gy
i imaii ii. -xi-
<6 5
Pr<Jpf rty
■ 11111 -1111IJ111.
4.7 S«f lk MATEfaAL.
4.5 Sand..
4.1 J GRadkriiM cupw /and
4.9 Design Of FMter ..
4 « / Gtfwrol ..
4 ft 2 Sm/ Fttfirr Drjifn
4 ft J DfJijw t/Trannlr-Dn* Ed4rr
i ir n iirmnirmin Hm n rnn i-
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s SErswrcirr
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3/
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37
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4.3
I
37
IIIIHIIIIIIHIIMJIUUIU
Water Warts Design LSuperriston Enterprise
tn luadatuiiwiUi intematifleoto toinuicuuiMTwiuiacriti m Ltd.Ado DfldeEJi IrrifsUcHt Project
Dam AppuHQD&nt Works
5.1 GEKER*x.
5 2 Sf I5MCITY QF TK REGlOri
5.3 DESiO SEigkwC COEFfiCiEFrrS
5 4 SE15MJC HaMD Map OF EIHOPwl...................... s 5 HQIWOn r al sEiSmiC cOt*FiG£mJ ..
a (JAM HEIGHT
6 1 General
6 2A ft Eview Of the f revkhjs studies. majde ...
6 3 The PmsemT Dam Height
04 Face Board
6 t 2 CowJuraurcir/iM" A'drww/ Frer fltarrf flf //if
m j an?
■ *ii&.iia.i-i.ii
...
4]
45
■45
45
IIIIIBUIIIII
■ ■.
in
...         4 ■
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□■■4 4 MMMum Frtrc iflika-J di MWl
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AMb^dr AfH't
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d 4 7 FufJ jRfjervtMr Lmf
■5.4 ff AftnrjHHffl £>o* Awn £<yti‘ FMCMUj
<5.4 ? CbHfrrf £<w«'
7 DESIGN ASPECTS
7 1 GfwEfeAix
7 / /         f «nf«c.-.nk."-j-.nl 'Fcdfuftt-J
7 i 1 i Grti WV*"n
Illi IB ■■■IIIJ II
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7 114 Pvipci MVaJl
7 1 15                 5-inmei
7.2 Design Pammeter............................... ...        ............. . . 7 3 Ha.SIC. Clf SXXi flEQtrtAFMThT
? J / JuT/riy
7 j.J i Fr«jUtekH-jf
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7.1.2 ErtfcfrclHjt’Hf flr fltaifalt ...
7 J J ZiVUrtg Ci* fn7-” iSwTrOJT
... . ......... .. ..
7|1
/■■ w 1
7 4 Founciatkw Treatueht ...
..     .
7 -4 j* C«X*
TrconwAi
7 4 - ShtJJ Fi>uAiurjLifli i7fji.stt.ni.
7 4 J Ciirqf rnrwA . ...
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74.4 iocaion iyCrf <j^7’Hr»vft...... .... .... ............................ .................... ... ..
7.4.5 CiBrfiBH jTttufrNg'
.....
..
.
7.5 Stability of the. lartn ahdaock*^ Dam Section... 7 fi SAFET* AAAIMST Nit Anal B©SO«
. ............
7 d. J 5mrhTffc Tatum irf-ranurrr am/ 7 4 7 ’nrl'i nrirf F jff#r
7 S 2 I CampBcbcn □* Fiftr
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64
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65
66
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67
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72
7 7            SAFETY OF SLOPES
23
7 7 J /An iJn-im floor Pf nfadflfth
7 7 7 TJv rdfi fair rift
? 7 j fTir Fhiff^prdf r(*'l ffjp Jd^p rtUCArtt* If
.. 7J
74
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... .74
7 75 CIM1,Tpw«
n/rgtfr'dUni
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................. ...................................... ............ ............... . l4iaSIIIII«IIIIY*«1ll
?J
....... .. .... TO TO
.. .7?
77
.... .....77
iiii
Wtttr Worts Deilpi A Suporrtilon Rniirpruo
[d IsrtdtOon wlcfi liiierMDULEOtil CodmUUQU M<1 Tfthnaaiu M Ltd.Ar)o-Dedtxsi Irrif niiati Project
Dim Appurtenant Works
S RIVF.R D1VFRSIQN
a 1 RivEfi OvtitSlOM ARRANGEMENTS .
9 INSTRUMEkTATlON...
9 i General
9.2 Purpose of Instrumentaroh 9.3 Types of Measurement
9J2
9 3 J S/r/xtf r        teakagr 9/4 Sfrffjnj ond sfrelsti
0 3.5 Z^rnamic toad ZSruwwy
9 J.9 OfUrr wa; wrrBirnij
MiyZOO?
lli:illli*illilBliliaiHiiiliiHniBi
■ JIIIUIIAII.il
IHMfllBIBBMIllH-VVVI
11 s e f 11 ■ ■ — ■ ■ i --■ ■ ■
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tj
9j
.n.ian mi.uulu
fl 4 PlANMNC C* IhST^LKmT^ThJhS FC* Th£ D**a
94 J Port wairrpressure
9 4 2 Seepage
94 J Surface m(7vr»w»w f^raiur*w«i 9 4 4 P&vpti Jfrtf/r-wMf Po«*w
mi i-iii iiiwuitf in-""iFfr*"""'
mi ii11rm n 'isr?—■• 
P 4 J /tortgMto/ tind
9 Y fr £arT »i^c.£Ulz 4^diiu/r»nr »tf
P 4 7 Other Measure/*™
10 SPILLWAYS FACILITIES..
lOl GENERAL.
101 LOCAT|O<4..._.
lO3Sl^kWAT LavQUT .
Mflvtnwft1 AiftHurf nwrntf
UI»4U4l-IHIb4U I
^aaawaaaa. . . aavwM niMrw!r*tirv .a<
PJ p- P?
92
n
92
7J PJ
PJ
Pi
P*
......93
____ 9?
____ 9?
.■_.■■■■&—.IliSUa.
10-4 DE3W INFLOW F.QOC- DISCHARGE.
10 5 Gatfc wjs undated Spillway.............. 10 B Energy Oss pation Arrajmgebent .
1 7 Approach Chanmel
1 D.B SphlWA* Structure ..
ID.9 Ogee Weir Profile.
10 10 Spillway Chute .
1 D.l 1 Structural. Nio^iremcwi __________
10.12FuOMUHWS
ill aawaaa aawtaaaaaai
10.11 Water stops amo joints
1D 14 DRajNAGE SWBL.
i D.l 5 HrDRAduc Model Studies of srllway structure ..._.
1 D.16 Z&MNG oF Material FOR W SPhlway JAdunts__________ ___
IIIIUBNIIII
11 HYDRAULIC DESIGN ....
n iirr-ii m =i 11 twi i n
J2
11 1 kydraujc Design of Spillway Facilities.................
H.2 iRKGATCWOVRETS.
11.3 IRTOGATKJN CUTLET f Qft RlGHT BANK PRIMARY CANAL  ... H.4 iRfcsSAiKiw t>ntET*0R left RanhPrimary Omrl..
11.5 HvOA*ui ic                     Qf iwtHjAiw* Outlet .. ti.si-rrtAAjucc«>CHC*iww*Ti(M outlet fob .
HYDRO POWER GENERATION
122
i2 2 Imcidemtal Power Genera ton
123 GENERATION OF OFTWUM Htoro-pcwer........ 12 4 Need FOR PHE-FEASIBlIJrT STUDY _____ ___ ...
REEFJtENCES
.... -..aa.H
... 9S
•••»•••••»• 99
10] to J
101
101
..... -106
106
.... 114
114
.... Hi
JIS
J 22
ID
i2 J
126
m
Hi
W*t«r Wort» Do si pi & Soportlsloti Enurprlse
In
with Inivred-DtiziQOUl
md TecImoeniU Prt Lid.Arja Dedcua InlfartM Project
Dun Appurtenant Works
Nay ZDO7
LIST OF TABLE
* 1 LOCATiQmOF BORROW AreasFdh CONSTRUCTION MATERIALS.......................................... ......... ............... . JI
T Mile 4 2 SELECTED DfSifiN Sand Filter Band_______________ _________ -............. ............. ................................ 4U Table 6 1 EfFECiMt Fetch Length(f,iComputaho for Normal Free Board
Table $2 Effective Fetch Length {fj Commutation for minimum Freeboard
44
32
Tabus 6.3 Free Board Cquputaikins........................... ................. ........................ ........ .. .................................................. .. ..... ................ 57
Table 7 1 Zoning Of Dam Sec now ■ Material Ttpes............................................................................ .. .............. ............ bl Table 7 1 Minwuu de sired Values OF Factors 0* Safety and Type of Shear Strength fcrVafucxfs
LOalang Conditions .......................... ... ....................................„.......
Ta>ls  7  3
Table    7.4
Table  7  5
Table     7.6
Table  5  1 Tam    10    1 tame u t
Properties of the oss»gn parameter for the clav core .,
,
................ .. ..............
Rdck c*esi0n Parameter. ...—...T^_..n. .............................. ■■■■.............................. . ...mu...—.^-. ............................................................ .
Stamutt Analysis - upstream Slope
Stability Analysis ■ Downstream Slope ............................... . .............. ........... ........ ................................ b;
Routed DEStOHF^ooo for FbvERDwtRSiON........................... ........ ...................................... ......... ....................................B3
Routed Design flooq Based on LlG Uuuhbu nc*. Peak out flow i95G m37sec ......................................... _..«
ARJO DEDESSA irrigation PROJECT........................................... .......... .................................................. ................ ..... _121
UST OF FIGURE
FIGURE
2   1   Map   5*0*11*0   OiLL   HOLES   LDGATON   AJOK
DAM   AXIS
11
FIGURE 4.1 MAP SH0W1MG BQftROW AREAS ..
.........................................
FIGURE 4.1 PLASTICITY CHART
................................
Ji
FIGURE 4 3 Clay samp le from chewq BORROW ................
.......................................
.
U1
FIGURE 4 4 ACTIVITY CHART ...
..
..
_______'■ „______________ 34
FIGJRE 4 5 CLASSlF iCATiOH CHART FOR SWELLING POTENTIAL.........................
Figure 4 e sand from all sources....
......................
jh
FIGURE 4.7 DESIGN OF GRADATION OF SAND FILTER :FQR ClA Y ...............................
FIGURES.! SEISM.iCLTY OF ETHLOPIA.....................................
FIGURE 5 J HAZARD MAP Of ETHIOPIA  .... .. . ......
FlGlfi£?1 DAM 5ECTVON STABILITY UPSTREAM SLOPE.
FIGURE 7.2 DAM SECTION STABILITY ANALYSIS OF DAU SLOPE FIGURE 7 3 DAM SECTION STABILITY AWTSiS - DOWN STREAM SLOPE FIGURE 111 BlEvaHoh-Amea-C^pacity CUKvtS 0* Aakj DeeCSsa Reservoir
44
.................. .. ............................ 44
_____________  _________________ _________ TO
.... ...
tn
iiimiiiiiniiiiu.aiii;i — ■
.... Il 2$
tv
Water Warks Ik si^n ISuperrtslon Enterprise
la UmcUUob with latoncDtmeBtal CwunltiJiti and TochMerita Prt IMArj oDtdejsi Imgidon Project
Dam Appurtenant Works
May 2007
LIST OF DRAWINGS
3 No
1         Location Map of Project
□rawing Details
Drawing No
AD F-Dam i 01
2
Layout Plan of Dam A AppurfenaM Slruclur*
02
3
Dam uayom Plan
03
4
Dam cross section at Deepest over ted
04
5
Dam Cross Section A A to D D
05
6
Gemogicu; Section aiong am erf dam showing mgeon wames
05
7
Geological section amg axis and AD 2
h
07
9
Geological sedian along aws erf dam A AD-7
" 06
9
Geoiogcal sectxxi along Saddle Area
’
OS
10
Geological seebon along Spillway
10
11
Dam - Longftudir.al section A curtain grouting
11
12
Cut off trench - grouting pattern
H 12
13
Dam Cresl 3 Toe detail?
"
13
U
Surface drainage Plan on Oj's slope of Dam
"
14
15
Surface drainage Dram Section
H
15
13
Pan snowing Surface arw parapet letbemenL paints
16
17
Section A*A
H
1?
19
Section e e
13
19
Section C - C
ig
20
Spftway layout p*an
* 20
21
Spillway Elevation and seaion
21
22
Spillway Longrtudmai seetpn and Plan
* 22
23
Sprtway - Dr* channel sections (1/2)
23
24
Spillway - D.’s channel section (2/2) layout plan
24
25
Right Bank irrigation outlet
25
36
Rignt Ben* rngabon oirtW Longitudinal secton
" 26
27
left Bank imgaOon outlet Layout pian
27
23
Lett Bank imgadion ouOet Longrtudmai leciipn
" 26
29
Construe ton Joint Details
H
29
30
River Dhwnlon during CtiMTuCttWi - Layout Plan
“
30
31
Rrwr Drwrwn dunng corwtrudkMi- LongrfudiMi seebon
31
32
River Dversion Duct Details
32
PHOTOGRAPHS
Water Works Design L Suparvtslon Enterprise
tn iuadiflDi! vtlb LaKnXUUftttVM CetmlUuftt mW T*elino<nu l*n. Ltd.Arjo Dedeua litigation Projtcz Dam Appurtenant Works
Ma, 2007
PHOTO I
DAM SITE AN0 ABUTMENT LANDFORM
PHOTO?
KOCK OUTCROP a r RIVBtBED UPSTREAM of Dam site
FHOTO J
ROCK OUTCROP Al Rl VERBI:D UPSTREAM Of DAM StTE
FHOTO4
RE SERVOIKaREa UPSTREAM OF DAM SITE
PI IDTfll S- REXiE of Right abutwemt
APPENDIX
aww-*
A Labor* tcs t Tests Resllts-of Borro* are* viateriau
Water Works Deilgn t Supervision Enterprise
la AHMi>nna alihliiWKtntlDentilCotuuluiitt ud TumumisPn. Lt4Ard D Dcdessa Inlflden frojBtt
Daw Appurteount Works
ACRONYMS
Majr 20C7
mA
*v
BCEOM
BIS
C
COSCO
CFRD
CUSEC
Cu
cv 
□m DfS EL EQ
Fr
%
FOS
F
Fe
FRL
GPS
GLE
Ht
Ho
ha
H
Hd
IS
L.
Lb
LL
M
horizontal Seismic Coefficient
Vertical Seismic Coefficient
French Engineering Consonant in association wi1h IS-L and
BRGM
Bureau of Indian Standard
Effective Cohesion
Construction Design in Share Company
Concrete faced Rock fill dam
Cuoc Meter per Second
Coefficient of Uniformity
Coefficient of Curvature
Average Depth of Water
Down Stream
Elevation
Earth Quake
horizontal force equilibrium
Moment Equilibrium
Factor of Safety
Fetch Length «n Km
Effective fetch length
Full Reservoir Level
Global Positioning System
General Limit Equihbnum
Significant Wave height
design Wave height
hectare
rieignt of Dam
head over Crest
Indian Standard
Wave Length
Length of Basin
Liquid Limit
MiBon
Water Works Design & Supervtsloo Enterprise
vi i
IP AxhcIsUjs Tliti talarHiiillfleaLiJ Coosu: LaoCs sod "whoccnts Ptt Ltd.Arjo Oedessi irrigation Project Dim Appurtenant Works
MCWR
MWL
Mmislry al Water Resources
Maximum Water Level
MOD
Maxrm urn Dry Density
MDDl
Minimum Draw Down Level
NMC
Natural Moisture Content
OMC
OpWnum Moisture Content
Pi
Plasticity Index
FL
Plastic Limit
PMF
ProtraCle M3x«tum Flow
♦
Angle G1 Internal Fnctinn
Q
Discharge
R
Wave Run up
ROC
Reinforced Cement Concrete
RD
Relative Density
Ru
Pore Water Pressure
S
Slope
TBL
Top of Buna uevei
TEL
Total Energy Line
U/S
JSBR
Upstream
Uruted Stores Bureau ol Reclamation
UTM
Untvwtal Transfer Mercator
V
Veocrfy of Ftow
VES
Vertical Efectricil Sounding
w
TQp Width Of Crest of Oem
WAPCOS
Water ano Power Consultancy Services {India) Lanitad.
VW/DSE
Waler Warks Design A Supervision Enterprise
VIII
Water Works De sign fc SuperrisLon Enterprise
In jLtiOc11t3&B vHfa IntirecotlueaLiJ CoosullAiiLS u,d TKtocerati FrL. Ltd.Arjfl-reae iu Irrt^iuon Project
Dam Appurtenant Work s
Miy2OT7
1 INTRODUCTION
1.1 General
Arjn-Dedes&a Irrigation Project Comprises at 40 0 m high Sarin and fOCfc fill dam on nver
□edesw  for  impounding  inflows  of  the  nvfrr  duhng  me  monsoon  period  The  Stored  w&ler  wall be  diverted  into  cam)  sysiem  on  tom  the  right  and  iefi  twik  for  providing  water  mrougn  a network of canal aydam for irrigation at a command of about 13.655 hectares of ungaolt land
Thengnt bank of tne aam is located In Wama Maribo Keboie ol Limu Saka u-uoreda unoer Jima Zona The left bank S located IS Cnftu Bosona KebelE of Guchi vVoreda of Lllubor zone of Oramiya Regional state Of Ethiopia The project IS locaLed about 360 knta from Aadts Abaoa and is accessible Beoeie ^iich ts about 40 kms from the project sde Location Map of the Project Area is available al Fig aD-F-DaM/Oi
The aam comprises &1
Chute Spillway on mr right Hann located m me nihm saddle f*o . ic* passing floods  waters  chai may  impinge che raeatvar « full reservoir lever co i«W overtopping oi me cam
iij An irrtgacion outlet wcatw m me saddle No H m dose proximdy  to saddle No i i&r drawing water from the reservoir for the ngne bank primary  canal and the distribution system of canai network
ik) A second irrigation outlet taking Off al th# left abui™rvt of the dam lor drawing water from the reservoir lor tne tert bank pnmary canal and drslnhutKm system of canal network
tv)   The   general   layout   plan   or   tn*   dam   and   appurtenant   structure   are   shown   irr drawing No AD^F. DAMlflE
1,2 Background & Review of Previous Studies
Various Studies have Men made since 19&4 by different organizairOPS lor development oi water resources in me country United Stales Bureau of Reclamation {USBRi maos the first Sludy litlea "La nd and water resources of the Blue Nile Basin' ih 1964 Durmg their study of Btue Nile Basin number of potential sites nave been lOOntlfiad for development of irrigation ano hydroelectric power generation m Dedessa valley Amongst the numerous sites identified USSR has proposed cam Site □□ 11 on river Deoessa fpr development of rrngafion ano power
1
____ _ __________________________
Waler Works Design £ Supervision Enterprise in JLmdatiDn wilk [tnecnocintnul C&nsiiltsm* kaaTcclmdcnuPvL Ltd.Arjo Dedewa Irrtgiiko Project
Dam Appurtenant Works
They had proposed a ute DEJ-13 as an alternative to DO-il and caiteo it Duia dam arte
MiyZOtf
Another site mentioned m their report is located about 1 5 km on river DMKsa upstream of the confluence of Dedessa nvar ana Warn a nver
The second study ‘Preliminary Waler Resources Development Master Plan tor Ethiopia' was made toy Water ano Power Consultancy sennce (India) Limited (WAPCOS) in the year 199C They proposed a site for location of (he dam on river Dedesia about M kms upstream of the dam site proposed by JSBR The mam reason for shifting the dam site is slated to be due to geological considerations. Due to 1he upstream locanor of the dam there has been an increase m the imgalKin Dgmmand area by covering areas ai higher levels under irrigation The project «a planned exclusively for providing irngalion without any generation of hydroelectric power
The third and the last study was made by BCEOM in the year 1999 in their study report titled 'Abtwy River Basin investigation Development Master Plan' the proposed dam srte is at the same location as has been suggested by USSR In their review repon an observation has been made on the fraaurahons wrmcn is highly developea in the Basalt rock end will require large and intensive grouting worn Faults discovered m the left and ngftt bank abutments will result is possible leakage points, tn addition, the faulting system detected on both the Banks and highly fracturing pattern already mentioned by JSBR, will increase the nsk of leakage Due to (he extensive drilling investigations program required to study the geology ano possible leakage problems the site has not been considered
The dam site DO-it on over Deoessa identified initially by United States Bureau of Reclamation and later reviewed by BCEOM were al reconnaissance level and no field investigations have been done Due to a major fault passing through the nghr and left abutments ana highly developed fracturation partem in Basalt rock requiring extensive and intensive grouting wort, the site is considered not favourable
2
Waterworks Dengu & Supervision Enterprise
In itsnetabon with lnur»nftnsnlal Ceuullaiiu and TwhEDcrau ftn. Ltd.Ar}o Dtdessi Irrt^SUon Preset
Dam Appurtenant Works
1.3.1  Type of Dam
Kay 20C7
Tilt dam site is located m a narrow gorge lormed By the erosion of over How and the topography suggests adopting a concrete dam secl-on However, tne foundation roc* in general at the dam site location as revested during foundation investigation 13 found to tie fractured and vesicular Berth the abutment along the dam ans are covered by Trachyte and
Traohy - Basalt and the part which are cnaractenzM by Trachy-Basslt ano vesicular es not conducive to conslnjction of a concrete dam The valley floor u covereo wrlh soil cover of varying thickness. Thus lhe choice of cam type gets limited to ertner an earthfill gam or an earth and rock fill dam with a central core of impervious earth matenai ana is governed primarily by the reLafrva economy that can be effected by making best use of th* available matenals in the vicinity of the dam site
Th*  materials  for  construction  of  an  earth  and  rockliH  dam  are  available  in  adequate  quantities
■ mpervibuS clay with the required engineering prOpeniM is available in sufficient quantity in the adjoining  borrow  areas  m  as  welt  outside  the  reservoir  area  The  rowfill  material  for  the  shell ion*  and  rock  riprap  for  upstream  slope  protection  of  th*  cam  ar*  also  available  m  the  near  by quarry area m adequate quantities meeting the requirements.
in the previous studies made, a flexible dam strudur* has been proposed An earth ano rockfill aam wHh lop width of 10.0m and central rolled earthfill section protected by with rockfilt matenai was proposed by USBR A dam with central roiled earinfill section with rockfill protection was suggested by WAPCOS BCEOM n«d proposed a compacted rockfill dam with upstream concrete feeing (CFRDy and a filter has been provided all aiong th* upstream facing underneath the concrete facing The rocxfill dam is founded on firm foundation with layers of fitter material provided above the firm foundation.
Therefore considering the various aspects, a central rolled earth fin section of impervious day core flanked Dy rockfill as sneli material with filter on both upstream and downstream lace of cenlrai day core has been adoptee lor the Arjo ■ Dedessa Dam
1.2.1  D»m Section
In the previous studies carneo out an earth and rock fill dam with central core of rolled earth fill riM been suggested by USBR. The central core is provided wnh side slopes on both faces of
3
Water Wort* Design & Snpertlslon Enterprise
tn IssocUdaQ aid! lateneoUsuila] CoaiUtliati and TeduwaSU PTt- U4.Arjo Oedessa Irrigation Project
Dam Appurtenant Works
May 2007
J/2   H   IV   The   upstream   face   of   the   dam   section   is   provided   with   2   3H   IV   stope   while downstream face of dam section slope is 2H 1V upto certain height ano there after slope c<
2 5h 1V upto ground level
The centra) rolled earth fill core rs covered with shelf material consisting of rock fill material oom on the upstream and downstream of rolled earth fill core A clay blanket has been provided m the nver bed and al abutments on the upstream The dam has been provioed with cot off trench upto firm foundation with sxfe stopes in the cut off trench of l| H 1V and grout curtain with grout cap has been provided
VvAPCOS had suggested an earth and rock fill dam with crest of lOCm width and the central impervious day core is provided with side slopes on both faces of 1H1V The upstream surface s-ope has been provided slope of 3 0 h IV and downstream (ace slope of 2H iv upto certain height and thereafter 3 0 H IV upto ground level A horizontal drainage fitter ending into the loe drain has been provided The impervious day core is flannea by rock fin as shell material The cut off trench has been taken to firm rock foundation
8CEOM (1999) had suggested a compacted rock fill dam section with upstream concrete fadng (CFRDj of 3.0 m thickness and crest width of 8 0 m A filter has been provided below the upstream concrete facing all along the upstream face and for a short length on the downstream face at the downstream toe of oam Upstream face of the dam has been provided a slope of 15 H 1V and downstream face slope of 1.3 H 1V. The upstream surface of the dam IS protected by concrete faeng all along the slope The rock fill dam has been founded on firm rocs, founoation and provided with three rows of curtam grouting at the toe of the aam upstream of the concrete facing with a deep central grout curtain and the other two adjoining grout curtains to check the seepage at the foundation level
The avarlacxlity and suitability of impervious day material for the core and cock fill for the shell of the dam has been established within reasonable distance Hence a dam with a central impervious day core with rock fill forming the shell zone has been adopted A fitter is provided on both upstream and downstream faces of the central day core The dam cresi of 10 0 m width has been proposed The parameters of the earth ano rock fi« dam and other appurtenani works has been described in subsequent chapters of the report Upstream surface slope of the dam has been proposed Io have a slope of 2.0 H:1V upto EL 1340.6 and thereafter 2 5H IV upto ground level The downstream face slope of 1.5 H: 1V has been adopted after carrying
4
Water Works Design & Supervision enterpriseArlfl-Dedessa lrri|*Ug> Project
DamAppunenint         Works
Kay 3007
out  the  stability  analysis  of  the  maximum  dam  section  using  SLOPE  AW  and  SEEPAA  software developed by Geo-siope international i Canada/
1.2.3   Dam Foundation Treatment
JSBR (1964J had proposed an earth and rock fill dam with a posdnre cu1 bfl by taxing the CUI off trench to firm roc* foundation for wte 00-11 The CUI off iren*h has been proposed covering the full width of the central core of rolled earth fill
WAPCQS had suggested an rolled earth fill dam section with positive cutoff by taking me cutoff Pench covering the lull width of rolled earth fill section up to roc* foundation BECOM in their study had proposed the enure rock fill dam section founded on firm roc* foundation and provioed with three rows or curiam grouting in a trencn width of 10 0 m on the upstream toe of the dam in continuity with the upstream concrete facing The central grout curiam is taken 60 0 m deep with ine aqj&mng grout Curiam on the upstream and downstream to 30 0 m ceplh to Check the seepage flaw in the dam foundation
The overlxiraen of loose material n the over bed varying (ram 5.0 m Io 10 0 m depth at the um site location is encountered The central impervious aay core of the dam founded on firth roc* foundation with curtain grouting in two rows proposed to be provided central reacn of (he wakey and grout cap provided to check dam foundation seepage. The grout curtain na$ been provided up to depth of H and the two adjoining gram curiam rows to be la*en to H/2 depth (H being the hydraulic height of the dam/ in the valley terrace and river bed reach, Blanket grouting covering the full length Of Cut off trench along (he toll length of axis of dam has been provided
1.3   The Present Dam Site
Subsequently during the year 2005. a team pf experts tram MOWR ang Water Wont* DoS gn ano Supervision Enterprise (WWDSE) during their visit to the project area identified a dam site which is located 1.5 km upslream from the confluence of Deaessa river and Wama river neat Ar|o m Jima zone This site for location of dam ana appurtenant vmrfcs was subsequenlly visited by a team experts from ICT (India) & after examining various aspects the site was considered suitable ana reeommenoea tor development The dam axis has been aligned cofttidenng the topography of (he ridge and both nghi and left abutments The onentation and axis of the dam is defined by point DA.-1 on the left abutment and DA-2 on the right abutment The latitude and
_________________________________________________________________________________ 5 Water WotkE Design t SupcrvUloo Enterprise
to AsudaUDit with ImtmoUDCQUl CsuulluU ud Teeitnflcrm m LU*
I hntueniDti I - Darn Sue and rhe Abutments Landform
Photograph 2 — Rock Out Crop al Rher bed I pslrcxm of Dani xi|?ArJoDetkisa Irrleauoo FToject
Dam Appurtenant Works
1117 2007
longdude and lhe coordinates of lhe dam axis in dangers and tn JTM geographic coordinate syslem are given below
ueft Abutment Point DA-1 Latitude                36° - 39* - 57 31" E
vongitude
8° - 31 - 04 24" N
Easting
243048 m
Northing
942237 m
Right Abutmem Pant DA-2 Latitude               36° - 40 - 06-38'' E
Longitude
80-3V- 17 48* N
Easting
243328 m
Northing
942653 m
The layout plan of the dam ano rts onentation is snown m drawing No. AD-F-DAM/03 The field investigations of the dam site reveaed that matenals of construction for an earth and roc* fill
dam with central impervious clay cove are available m suffkaent quantity and is not a constraint The staaiity analysts of the dam section, s/ope protection works and seepage control measures below foundation are described in subsequent chapters of this report
Ago-Dedessa dam site is located in the western plateau of E(h»opia and is far away from the Afar and main Ethiopian rift The oam lies m an area of medium to low seismic activity a horizontal seismic coefficient of 0 05 g has been adopted and vertical seismic coefficient taken as half of horizontal seismic coefficient of 0 025 g is considered These seismic coefficients values have been considered as per the seismic hazard map of Ethiopia and dam section analysis has been earned out with these vatues
The topographical surveys geotog-cal and geo-technical investigations and other related studies have been earned out for the earth and rock fill oam at this location for the preparation of the feasibility study report
t
Water Works Design & Supervision Enterprise
to Auedatloo with IrteroiitiiienlaJ CcnnJtuu and Techno crats Pvt Ltd.Photograph 5 - Ridge of Right Abutment■IrjoHfdtsii IrrHitlcn Project
Data Appune d ani Works
1 GEOLOGY
2J General
m iy am
i^wous roots, different v&lcenic flows and bas*c intrusions trial come through the regional laun Ines and localized fissures typrfy the bedrock geology of the project Hrea The resi o! the area if IS covered by alluvia, residual and colluvial soils The vacant rocks are exposeo in creeks abutments river bed and hills of the project area Further down stream of the dam axis, aro-jno mrf way of command area following the river Deoessa and on the right Side metamorphic rock ts aiso out cropping
Geological mapping was done on 0am axis, saddle dam, ano reserv&r area and On construction material sites This geological mapping targeted on identifying different rock and sod units, measuring fractures and joints on the out crops and verifying regional and local geological Structures in the pro|e« area More ever exploratory horerioies were dtdled on different part of the project area
22 Dam site
Geomcxpnoiogicatty the dam site is cnaractenzea try two relatively steep mlH. Which are known
as the abutments, end reiaLveiy flat nver cnannel in between these abutments Alkft ne vertical dikes cover the slope and top of (he abutments, which gave sleep Landform Five exploratory oorehcues were drilled along the dam am in order Ic verify the type and quality of the rocks. permeatnHy of the ground and other geotechnics* parameters and are indicated in Figure 2.1
2.2.1 Left Abutment
Three exporaiory boreholes were tinted on the »ft abutment *1 order to investigate the ground conditions In addition to drilling the borehotes. vertical electncal soundings (YES) survey was conducted m between the boreholes. The result of investigations snows that alkaline volcanic jocks, which are composed of alkaline basa^, trachyte basalt win vesicular nature end aphanatic basalt, cover the abutment, “he alkaline volcanic rocks, which are exposed at the dam axis occur as a dike, and it ahgn m NE direction. On the exposures the alkaline volcanic rock is highly to completely weathered, the fresh part is pinkish m color composed of alkali
10
Water Works Design & Supervision Enterprise
Id AmocUUod With Intxrco cUnentxl CansalUnu ud Techaocnu 2tL LU.Arjo Dtdcjsa irntnuoD Prajen
Dam Appurtcusfll Works
May 2007
K-leMspars and afftcied by ciosely spaced fradures and joints No fresh rw> nad been encountered even by drying up to 1he depth 40 m m bore holes AD-2 and AD-1 except Fresh casadhC /dolenbo1 intrusions in 1he twrehote AD-7 Just 70m downstream from the borecole AD-2 (he depth m wOch this dolerelic roc* S encountered is 9m It is not observed in the othe' boreholes along the dam axis This bas-it roc* from Che borehole AD-7 is very strong, fresh to slightly weathered and occur? as a dike
The amount of leakage in the Doreholes AD-1 and AD-2 especially from the depth 6 to 13 m is unacceptable d ■$ in the range of 38 ano 26 Lugeon Further oeep the test result snows mat the Lugecn value «s getting smaller and finally it is 0 tugeon. wruch implies thal the formation is becoming impermeable K can be said that this abutment is weathered to different wealhenrg profile, and the resulted day and silt fill the openings
2.2.2 Valtey Floor and River bed
Upper pari of the Left and ngln valley floor is covered by alluvial oeposrt and tfs thickness ranges from three to five meters These alluvial deposits are composed of $«'t and clay w+ircn were transposed by the river Dedessa. Due to its ongm and means of deposition, the formation u very loose Basaltic trachyte occurs under the alluvial deposit ano the river bed Up to lhe depth of 20 meter this formation is fractured, slightly to moderately weathered and Strong Two strike slip fauMineaments are observed at lhe loot Of both abutments. Due IO these geological structures the cores recovered from the oorenotes drilled on the valley floor are sheared and filled with white prec ipitaies The rock formation below the basaltic trachyte is trachyte, and d is solid, moderately strong to strong, fresh to slightly weathered with radiai porphyrite texture The fractures are mostly heated, mter connected and filled wflh white matenals
Water pressure fests were conducted tn both boreholes (AD-3 and AD-4) si every 5 meters The test results generally shew that the intake up Io the depth 50 m is moderate to hign i.e . in the range of 3 to 10 Lugeon m AD-3 and 6 Io 34 Lugeon in dial of the borehole AD-f Lugeon value and tested elevation rrterv* for each test is presented on the Drawing AD-F-DAMAK
12
Water Works Design A Superrislon Enterprise hi Ism riitlDn *111 [niencoQdittttij Co uitlcanu ud Teduuerats Ftl ltd.Arjo Dede»> Irrlgitlxin Project
Bam Appurtenant Works
2.2.3   The Right Abutment
Miyaxr
One exploratory borehol w» drilleq on me right asmmeni mtiologically the formanon on tnt
right abutment is uniform throughout the hole ano rt tan oe group™ as pinkish io pa# grtj
a»ah vacant rock The rock as rt observed from the exposure ana cores art strong
moderately weathered and Fraitureo
CpBuvigl deposits cover upstream and d&wnstfeam flank5 of the ahulment These colluvial deposits are decomposed mic clay Sanfl and graved. The Cia) materials fill the opening? m fractures, joints, ana dnooncmuities on coin laces cl the abutment Based on water intake amount from the packer tat in me ocwanoie AD-5 tne pans from me surface to the elevation 1335 m and below the elevation 1325 m are characterized by nigh Lugeon value, i.q 12 Id 27 Lugeon Accordingly the empunn of leakage is not acceptable and needs remedy like grouting aiong the line of stripping
2.3  Saddle Dam Sites
Two Saddles are tderrtrfted on |he nghd gipe Of the over Deaessa. Both Saddles are separated by small nlll witn the maximum eievaton of tSSQm amsi Geological end Geotechnical invesbgafron. wtncn compose geoiog*cai mapping, exploratory oorehoies ariMing wnn msrtu tesbng and mt pit excavation was done along me saddles and me hih Bases on the mvwtrgation me following three geological units are identified ano discussed beio* as follows
Soil cover
The upper top pad, with m>ckneM varying from i to em is covered by black sitty clay This sod is munea from me weathenng of alkali basalt. Il is very sutt, expansive ano needs 10 be removed for the consirucbon of me aimcrures.
Trachyte / Rhyolite
This rack IS exposed pn the hili in between the saddles and along lhe saddle areas under the soil cover Ltd thickness ranges from 7m in the hp*e ADS’t to 60 m at the hl. The rocks exposed at me hill vary from trachyte ip myplrte with In a few distances and fractured. The rock cores recovered from, both drill holes are weak and decomposed to sitty sandy gravel The permeability tests flailing head leilt fMuit shows Ehat the permeability rate vary from 3 05 E- 05lo 1.07 E-OA crrtfsecArj & OedEua IrrijatiflB Project
D&m Appurtenant Works
Basalt
MiyW
The last formation, wfitcn was encountered by doling and mapped tn the lows* elevation, al the bed of Wjma River, is basalt Tmj roqfc was found at an approximate elevation 133B m amsi in the coreTible ADS-1 araj ADS-2 it 13 fractured in the upper pad with some vertical joints strong to moderately weak, moderately to Slightly weathered wild some vehicular zone which are coalM by redd«sn to yellowish and some time whitish materials However oeiow me elevation 13-33 m n was found blocky, very strong with cpicrte mfillmgs al discontinuities ano vesicular zones. Concerning the water mtaice, the upper part 13 permeate with the Lugdon value ranging from 8 Io 12.
2.4 Geotogical Structures
Fauns, fractures. lineaments, bedding planes are geological structures that affect the stability ol dam and other infrastructure Consequently regional faults, local lineaments, and fractures are identified by desk study u$mg Areal pnotos and satellite imagery and th<3 had oeen confirmed on me fido through measuring joints, fractures ano faults and m exploratory boreholes drilled
Based on the investigations, two joint set directions (NE-SVY major and E-W minor fracture directions) were recorded at the dam Site According to the measurements and analysis the average dip amount of the enkre joni p*ane is greater or equal to 70° Analysis ano stereographic projection is presented on mam geological report Two E-W Lineaments cross the dam axis al the foot of both abulments. Consequently the water intake in the boreholes ciose lo (he Geological structures d high lo very high More ever one lineament with E-W direction is also verified ll the middle of nght abutment beyond the end point of dam axis Borehole AD-6 dnlleo at this lineamem. and the falling head test result ranges from 1.5BE-G4 to 8.+8E-05 on/sec. From the observation of the core of the hole AD-6. and (he result of falling head water intake, the lineament is filled by clay and sandy materials and hence hd serious leak age problem.
Other sets of geological structure tn the area are faults, which are aligned in parallel direction and located upstream and downstream of the dam am These faults flow major fault direction However since the dip amount is vertical 10 closely vertical, it a not expected lo cause major problem on mam cam except for the saddle dams As the result, remedy is recommended along the saddle.
14
Water Works Deslgp & SuperrLston Enterprise
In luodatinn with Intunxcttoentij Comuluau Bud TwluiMnij Ptl LuiArjo Dedessa Irrigation Project
Dam Appurtenant Works
3.     DAM FOUNDATION
3.1  General
MIJ2QC7
The Aijo-Oede»3 dam comprises at rignf abutment. nghi valley floor river bad. reft valley floor and me left eoutment All tbe&E ccmponenrs have different characteristics pnq require varying treatment in regard to stripping and protection measures against seepage below me dam foundation The ground characteristics at [he various Mdlm of the dam tounaabon and the geological set Up have heen describee m 1he eariier chapter-^ on Geology'
3.2  Stripping For Dam Foundation
Ths different sections or the a am foundation calls for smpping of ground Surface accordingly to the roCH grade aiocg the earn not? The excavation required to reach an acceptable foundation
•evel is CMItrent for the dam seating below imperious day core and uary For th* dam seating in roc* ftn tnel In ma rarer part n ts considered Oh geological assessment or (be rock grade for tne cut off trench
3.2.1  Excavation Below Core Seating
The  stripping  in  the  core  trench  part  would  he  considered  00  gecmjgicai  set  up  and  depends upon the ground conditions
■   The stopping for foundation for the core trefICh is 10 DC earned OUT 10 remove tsLUJ. loose matenai  and  weathered  rock  upto  a  Mvei  of  fresh  rock.  wh*ch  can  lake  up  me  grouting Ire at man I   The depth of excavation required to certain Suitable core I Ou nd alio fl is 10 considered Oh the basis Of assessment of the geotechnical EngineenGeolngist
■     The  core  and  filter  Inundation  surface  e  to  de  thoroughly  cleaned  using  |ngh  pressure  air water  jets  and  mechanized  equipment  Open  joints  and  minor  shear  zones  are  IO  DC excavated and cleaned to a minimum depth of three times the opening width artd sealed by fining with slush grout bSC* fib concrete. Shapng ot a hutments to provide gradual changes m  stopes  rs  important  where  maienaiS  with  large  difference  tn  Seformatnjn  modulus  ano compressibility  are  being  us«  Suth  »  rock  fill  and  a  sloping  ctoy  core  wi1h  high  m»|ure cement SutHtentut shapmfl wrth concrete may re neeoeo depend ng upon (ha contours.
The abutments of Aryo-Deoessa Dam are not strong as revealed by the rtelt notes investigations
■nd  therefore  would  require  special  measures  in  detailing  the  adjoining  embankment  zones  to be assessed jointly by the E ng irwer. In-Charge along with the geologist Particularly m case cd tefl abutment as the rock of the tefl abutment is weaker as compared to the rocks in the right
ts
Waterworks Design LSupcrrklon Enterprise
In JUndfttiOD With teuraatknesuJ CfinsnltiBta xndT*hH»xtt Ptl LUArp Dttessa Irncatlcm ProjErt
Dam Appurtenant Works
If nF 2007
abutment  Stability  of  toe  oam  section  has  been  enhanced  by  providing  widening  the  fill  ai ends This may be considered more economical than removing weak foundation material
The abutment and valley Stopes for excavation below core seat are trimmed or presplrt Io 1 i or preferably flatter Changes in valley Slopes al any point 13 to be not more than the 20° degrees, cavites and depressions are to be filler with dental concrete Over hangs god outcrops or distressed and fractured rocks on till) slopes along the axis of the dam need to be removed
in rhe event of getting irregular rock surface in cenam reaches then 0.5 m concrete thick Over the foundation surface supporting the core and titter on boln upstream ana downslream of core has been provided.
The arrangement pt excavation beiow the core seating of the dam in the cut off trench based on the aorxve consideration and the geotechnical assessment has been tndicaied in the Drawing No. AD-F-Damr The arrangement provides for removal of all loose material and weathered rack on the nght ano reft abutment upto groulaWe rock grade. The depth of the weathered rack is varying tn thickness from 4 0 m to 6 0 m on the right banx The depth of the weathered and loose rock on the left abutment is varying m thickness from 15 Om to 40 0 m The left bank rs found to have more depth of weathered rock as compared to the nght abutment. The exact required depth of excavation m toe cut off trench along the dam axis requires to be assessed by the Engineer in charge ana the geologist at the time of actual const ruction
Qn the right, and rttt abutment, the excavation of the loose rock tn the cut off trench is be carried out by manual wedging or by controaeo Wasting to avoid any shattering and damage to loDsecy jointed rock.
3.2.2  Excavation below Shell Zone
Foundation excavation under the shell zone will be required to reach foundation maLenals having shear strength and compressibility at beast comperabte to those of the compacted rock fill Talus deposit ano sols tike weathered row, shall be removed and founded on moderately weathered rock along the abutment side slopes
In the river channel, all alluvium deposits fl to excavated and toe shell tone to be founded on competent, mooeraiely weatoarea rock. Where sheer zones filled with pipable muenais underlie the downstream shell, it should be excavated and a fitter placed over the area to
_____________________________________________________________________________________ Water Works Design & Superrixlan Enterprise
In Aiwtdntidn With lrtarwrtlnetiui Consultants Ud TKhlwnU Pvt Lid.
16Arjo De dess* IrrlgtUcii Project
Dam Appurtenant Works
KsjrMO?
present piping Before laying the 1irsi layer of shell maternal in the river valley, the Inundation material is to oe thoroughly compacted by giving appropriate numoer of passes oi a wbraioiy roller after applying moisture io the required extent
In the valley area there is an overburden of riverine alluvium Deposit of about 3 0 m to 5 0 m Complete removal of this alluvium deposit may not be required btiow the seat of rocx fill srwll rone Only lhat muon hepth or alluvium where relative density (RD) of the ins-tu material is found to be less than 60% need to be removed in order to safe guard against liquefaction of this soil in me event of an occurrence of earthquake of high intensity The field relative densify value Dy standard penetration test may not give correcl values in Hnd iorm In that event the relative oensffy may be determmed by the relationship giver under-
r, -
<3 jrnin
rj
r d nw rf mlm
r
Where.
® relative densrty
r, ■ dry unit wetghl in densest scale
r
= dry unit weight m place
■tf
r
fl .m■an dry  u*nit  weight  m  loosest  stale
3,2,3  Foundation Treatment
The foundation is to be treated for providing minimum settlement lo the earth fi rock fill dam
The craots. faults or deep pits need lo be removed and oaacfilled with concrete AJI joints and
cracks beneath the core and filters are to be deanec and filled with concrete The foundation treatment must be sufficient to satisfy (he following criteria
I) Minimum leakage
h) Prevention of piping
lii) Limited settlement
tv) Sufficient friction development between abutments ana
foundation to Insure sliding stability
The fourtdabon nae been treated for preventing under seepage by cement grouting beneam the cutoff Besioes pervious zones upstream from the impervious membrane can be blanketed with mpervious material The foundation surface in the over valley zone will be moistened to the required extent before starting the operation of compacting by heavy vibratory rollers The
17
_
Water Woriu Design & Supervision Enterprise
In Jssectibca with lotens uUnental Co wnbLurti and TochnacrtU Pvt uaArJoDcdesjt Irrigation Project
Dun AppurtenuiL Works
K»y2OT7
ciay material in layers af 60 cm depth is placed at optimum moisture content (OMC) in me xnpervious core. The shell maienai layer is paced in the shed Jone in 10 m 'lifts lex compaction by requisite bumper of passes by heavy vibratory rollers to be determined by trial lesling
3.3  Grouting Requirements
Grouting is earned out to achieve the foliowing conditions for facilitating the safe design o1 (he dam
i}       To reduce the erosion potentei of seepage
ii)        To reduce the leakage through the dam founaanon
iii)        To reduce the sememehl ana Strengthen (he aam foundation
The geological assessment of both left and right abutment of Arp Decessa dam based on geotechnical investigations reveai the laa (hat the rock on both aoutments is highly pmted scoriaceOuS, fractured and vesicular Tracny Basalt. The rock on the left aoutmehi Is weak in comparison tQ the rock on (he right abutment of the dam. There are alternate layers of Traofty Sasart (bouKJerj and Trachy Bass'f as revealed tn the borehole taggings The permeability tests conducted on the drill holes etfiibit varying degrees of permeability values at different oepths in the same bore hoies indicating there by that the rock is nighty jomied and fissured. Three bore holes have seen drilled on left bank The permeability values exhibit high values varying tram 54 Lugeon at a depth ol 6.0 m io 40 Lugeons at 12 0m. depth in bore hme 'ADI at GPS elevation of 1358.0m. on left abutment
From the borehole logging and the permeability values rt tt evident fnat path the ngrit and left abutments and in the river bed iorw there rs new lor extensive grouting Consolidation grouting (o minimize the risk of excessive seepage from the water 1ace of impervious core with the foundation is required between the abutments along the dam axis The arrangement for consolidation grouting ano the curiam grouting proposed for the dam is indicated in the drawing NoAD-F-CAM/1
3,3.4  Curtain Grouting
The grouting shall be earned out through the grout holes drilled from tne cut off trench consisting of two rows of grout curiam to depth uptc K in me mam rwer reach or as per the Engineer-fn-Chargo. The number of rows rtf curtain grouting end the depth upto which grouting would be bone shall depend upon the assessment cf the foundation condition, permeability of ground strata and the geological set up forming the foundation of (he dam at the time of
I*
Water Works Design & Supervision Enterprise
la AuocUQnn with lewrreulhienikl ComuttuU ud Tectuumii Ptl Ltd.ArJ d Dedens Irrtgidon Project
Dam Appurtenant Works
MayZWJ
oonwruction The pattern of grc-jl holes an abutment ar*d tn the river valley is shown in the drawing Depending upon the width of me cm off trench, grouting pattern nas been adopted
For the Arjo-Dedessa dam foundation, one row of tunain grouting holes in the aDutment reacn where the cul off trench width is less than fl Omis proposed The grout holes shall be drived at 30m  center  !□  center  spacing  and  grouted  These  holes  art  primary  holes.  After  tne  grout  is set tee ptrcolairon test would be earned Oul «n check holes If tee strala shows after grouting the permeability of more 1han 3 Lugeons ano the quantity erf grout absorption of tnese primary holes shows significant increase. Then secondary hoteS shall be drilled in the miodte of the two rows  of  the  grout hoies  at  the intersection  of diagonals of the square and grouting shall  be continued in these secondary holes until the designed degree of impermeablizstion is achieved For  grouting  wfiti  cement  3fl  mm  diameter  notes  are  used  The  adventage  gained  by  oniing large nenes does not often justify lhe tftcrease in drilling costs, in long holes the diameter al the lop  of  the  holes  may  have  lo  De  larger  than  the  final  diameter  at  the  bottom  or  the  hoie  lo facilitate telescoping or to allow for wear of the M
in the central portion of the valley including tne nver where the core liencn gels veder n is proposed lo adopt two rows of curias grouting in order lo seal arger number of joints The depth upto which curiam grouting in done would depend upon tee geotechnical condition of the foundation rock The additional rows of grout holes on tne upstream sde and on the downstream of two lines will biso be drilled. The grout notes in lltese additional added rows is utilized for consolidation grouting The number of additional rows erf groul holes for consolidation grouting IS taken upto 10 0 m depth verlicalty Thus two pattern of grout botes have been adopted for Atp-Oeoessa aam The spacing tjrf grout notes wouw be changeo depending upon the results of the percolation lesls ano grout absorption rate regularly
The grouting snourd start wnh a low initial pressure of say 0 1 to 0.25 kgcm2/m erf wrden and butkJ up the pressure gradually. Initially the rate of intake may be 20 //mm to 30 f/nun In order to avoid the premature build of high pressure a general guideline should be followed thai tne pressure should be raised only when the intake race fafls be*ow 5 f rmin In the case of surface teak developing the pressure shouio immediately be reduced
The limiting value ol pressure for each zone and depth may be decided initially on the basis of categorization df rock and initial values to be confirmed fry |njl and observation The choice of pressure may also be established by results of tnai grouting along wite observation of upheaval by uplift gauge. Limiting pressures may be decided by continuous review of the trends ol pressure and rate of intake during grouting
_
Water Works Design & Supervision Enterprise
___________  _ 19
In luodsClo□ with IntArconttaentaJ CcosulumU and Technocrats M LtdArjo Dedtssa irrigation Project
Dam Appurtenant Works
4 CONSTRUCTION MATERIALS
MiyZW
The assessment of availability of construction material at proximal distance to the cam srie was one of the mayor tasks m the surface geological mapping geological and geo-iecnmcal investigation a The mayor construction matenai such as day. shell matenai. rocx for coarse aggregate np rap and sand were tdenlified m the upstream and downstream areas from the oam axis Extensive field traversing has been undertaken to locate the sources for differerri types of construction materials required for the dam and appurtenant worts These locations for the borrow areas lor construction materials for dam are shown an trw map available ai Figure 4 1
The clay materials are residual Mds which are insrtu formed soils found in small hiHs where new settler settles on most of lhem The selected sites for day material are m the upstream area from lhe dam axis on doth lefl ano ngnt of sides or rwertwrms The shell matenai is fractured and wealhered alkaline basalt downstream of lhe dam axis The rocx for coarse aggregate is apnanmic basalt located close to ATE village. The rock for rip rap proposed is the rwnnand irachyfic hill In tne command area and the sano material is in Ina downstream area ot Odessa valley The details of each construction matenai are described in the following sections
4,1    Borrow a rca a for clay
Five  areas  have  teen  ideniKieo  as  potential  source  for  Obtaining  trie  day  core  matenai  for construction of the dam The areas identified and their locations are given m Table 4 1.
20
Water Works Design A Supervision Enterprise
la UMtliflto with tnicmotlntou.1 Ceuultuts ud Technocrat! Fyl LidArj© Dtfessa Irrigation Project
Dam Appurtenant Works
Titjkf 4,1: Location nf Sorrow Areas For CONSTRUCTION MATERIALS
Kay 2007
Hem                             Estimated
i Dletance
from dam
site J km i
Locatior 1
J--- -
Site name
Typer  name  of  the
no
Volume <m )
a
Easting     Northing      materiel
Clay for core
1 Ale 31 541 58 3
244000      935329         Swtty clay
2          Chewe           . 345 327 50
5                      243550      938640         Sirty clay
3          Maribo            502 603.13          10 4          Ohendessa     ‘ 1 062 455 00   6
250000      93791C         Silty day
249725 [ 940140             Silty day
5          Obese            ' 140 567 56
4
Sum                             2 082 494 79 Aggregate
1         AOCAQ           >1 OOC 009
244805 946300 Silty ciay
—
5
243582
934698         Basalt
2          Maritxs            >1.000 000
-
2
247500
942350         Basatt
>2 000 000
Shell material
pi?   AOQl               >6624000
1                     242190      943*00
Trachy basalt
2          Gucbe
>3 000 000         12                    234489      943400
Basalt
>9 642 000
Ripra
1
Buxeta            180 000
6
249320      941079         Phonotite/T rachyle
2
CotiSin
120 000
26
224180      946815         Phonoiite/Trachyie
300 000
Sand
I
1
Borcne
60
959157
-
LO<O
sefera
■fl
6C
214802
211860
960600
■
3
L&kO
bodge
■
60
215289
961337
-
4
Tullu
senbete
■
65
i
■’
-
*    Not estimated
* Not accessible m wet seasons
21
Water Works Design & Stipei-rMon Enterprise
En tirtciidiio wi'± lut:reoctinea aI Consuttam and ThJji-jcwj fri LuL
jAfjaledust IrrtgiUta Preset
Dum Appurtenani Works
MiyMOT
Observation of Borrows areas ounng ihe ftekt vcrf id ifie pro^ct area showed Wat day maienai can be oorrow&a from [ne upstream areas from me dam Site The re&dual soils aL gently sloping small hiBs on bow sacs of IM <5 avaitabie 31 many plates. Location pl the borrow sites u snown in Figure 4.1 Accordingly the following sites were identified lex day borrow maienai investigation
■
ATE tillage area
■
Chewo tillage area
(ChB.1
•
One nd hens a tillage
(DhBj
•
Wama-Maribo school area
(MBf
•
Obese village area
(ATB Obose)
The Sites have peen marked on the map and hau e been OMignarK as DhB Mb Chfi. AtB ano
.,AtE  obose.  The  proposed  borrow  area  sites  ALE  arid  ChB  are  locales  in  We  led  Side  of Dedessa reservoir area eno other two sties namexy CfiH and MU ant local CO OH Che fr-gfil sdf cf Oeaessa reservoir area For 1he investigalion of the quality and volume Of the clay lYiaie/iais about  46  test  pits  are  dug  al  the  5  sites.  Test  pit  digging,  logging  End  bulk  sampling  are conducted Drfferenl types of samples were co I led ad from most of the Cast p Is anO imm each layer  in  We  pits  The  samples  wwe  analyzed  al  COSCos  laboratory  The  summary  of  the laboratory test results ol construction materials is shown in Annexur e - A.
4.1,1   ATE ares
The area n located about 6 km upstream of and on the left side of the cam axis adjoins co Chewo village and e 1 0 km upstream erf dry stream 'Adosa' The river 'Sioen is on Int so Ld hem side erf the visage ftowmg at a distance of about 3.0 Km, Red sdty clay with depths varying has been wca1*1 ih 10 NOs reprEsenlalrve test prts dug indicate depth of the silty clay varying m these pits Samples have been pgSlKted ana these on lesling m We latWteiory have ind rated the following average properties
1. Gram sue distribution
Sand
Finer
Gravel
5%
;
: O.0 %
____________________________________ n
Water Works Design t SapervUloa EntarprlBB
In JUwdatJtm with tat area hIUihb tel ConiultiiLti icd Twlmocriti Pvt Lid.Ar Jo Dedessi Imgatlon Project
Dim Appurtenant Worts
2         Attercerg s Limits
i. L+qurt Limit (LLj
li. Plastic LimtB (PL)
iii       Plasticity InOex (Pl)
MayZKJ?
63 0%
30 D%
25.0%
3     Fr« Swell
46%
4    Linear snnnltage
46.9%
5     Specific gravity
2.63
6      Permeability
205x10* cm/$«c
7.     Standara proctor test
L -Natural moisture contenl
150%
ii. OMC masture cement
30.0%
in. Marnmum Dry Density (MDD]
1346 hgim:
&
L Cu
38.8 W0H1
"■
26 6a
9
i. CV
26.5 KNim2
C. &
acr'.o
10
Coefficient of consolidation
0.234
11
Dispersrvity
Mn dispersive
4.1.2    Chewo village
The area t? lacsteo about 5.0 urn up stream or the arts of the Mm ana l$ on trie left oanh area El U Ciw to Ale vi dage and is on the down SfcltO Crf dry rtvtf Stream Ado» which ts very cinse by The borrow urea fees between Ale Village Ihd Chfiwt village Test pits have been dug In the area and silty day Ih those test pls HI deptTi varying has been estaolrsneq. The laboratory test conducted on those samples have Indicated the following average values
i Grain sire distributor*         Sand
Fines
Gravel
2 Altertoefgs Limits
Iv Liquid Lfrnta  (LL)
V Plaitifi Limits (PL)
vi, Plasticity Index (PI)
3, Free Swell
4. Linear shrinkage
5 7%
94.26%
0.0%
500%
36.0%
20.0 %
-
*7 06%
25
Waler Warks Design & SuperrtsiDD Entarprlsu
Is AuacUtlrrt With hUmnfloBDOi Camhuiti nd iKtatCTUI PH LU.Arjo Dedesii CrrlfiaoD Project
Dud Appurtenant Works
5     Specific gravity
6     Permeability
7.    Stanaarg Proctors test
i       Mturar moisture content
M. OMC moislure content
KU W
2 76
1 59*10* cm/$ec
8.0%
34 48 %
Jit, MDD
1429 kg/m3
B.
- Cu
35 5 KMrm3
ii * w
26flO
9
1. Cu
37 0 Khl/m3
i 0'
3(f.O
>0
Coefficient of consolidation
0,248
11
DiSperemty
Non despersve
4.1,3   Dendessa Area
The area ts situates about 6 0 km of dam axis and is on the right hank area of Diaessa River The dry river stream Chora is on the left side of the area The area lies dose io Amo artd Manix villages 12 Tests pits have been dug in ine area and these indicate presence of brownish red-fo-reo slfty day material varying tn depths over (he area.
Laboratory  tests  conducted  on  samples  collected  from  these  area  have  indicateo  the  following properties
i Grain size distribution Graver
Sand
Fines
2. Atierberg Limits (%)
i. Liquid Limits (IL)
ii. Plastic Linds (PL)
ii. Plasticity lndex(Pt)
3 Free Swell
4 Linear shrinkage
5. Specific gravity
6 Permeability
0.0%
3 5%
96 5%
640%
41 0%
23 0%
47 0%
52.13 %
1       2.7D%
3 14x10* criiVsec
____________________________ 24
Water Works Design & Supervision Enterprise
In AuadiUon »1U3 UuemDlloHlaJ CduuHailu udTetiuHnli Ptl Ltd.AljrttefaBi* lrrlf*tJ db Pre Jed
Dam App u rtenint Warks
7 Standard Proctors test
Miy2M7
■      Natural matslure
160%
t OMC
38.0%
< MOD
1378 eg/m3
6 L Cu
38 5 KN/m1
27° 0
9      L Cud
30 0 KNrmJ
ii pt-
yi’o
10. Coefficient or conwhdstipn
0 231
li OispersMty
Non despersrve
4.1 J Mi ribo village
The area is located 7 0 Km cw stream <rf the axis of the dam and lies near the village Dale and Amo village on the nghi bank area af the nvar There is a dry nver stream 'Cnwa' near I he area and aver Deoessa is Pawing about 2.0 rm from the borrow area Representative test pits in the area has been ouq and these indicate I he presence OF brownish ted and red sihy clay with the depth of silty clay materia* varying over Ebe area has been established Latxjraltyy tests samples From these pits callcclco from the area nave indicated the To 11 owing properties
1. Grain size distribution Grave:
Sand
Fines
2.Atterbergs Limits
vll. Liquid Limns (LL)
rlii piasbc Umlw (PL)
kx. PiastKfly inde^Pl)
□. Free gvrefl
4    Linear shrinkage
5    specific gravity
B. Permeability
7 Standard proctors test
i. Natural moisture
2%
3%
96%
67,0%
40 0%
20 0%
50 00%
57 94 %
2 63
6.2x10 cm/sec
12.0%
_____________________________________________________ _________________ 25 Witst Worii Design iiSuperrL^aq Enterprise
to luadailDB ellh tn u mu du an l£1 UtdtJLiaU udTcchuMnU m. LtiArjo-Beduai Irrttidon Project
Dim Appurtenant Works
■ OMC
lii. MOO
0 l. Cu
Mayzwz
ii fa'
10. DiSpersivity
<1.5 Obose Area
35 0%
1435 ng/m3
46 0 KISHm7
23 0’
27 5 KNfmZ
28  5°
Non dispersjve
The area is located about 4 em from lhe dem avis ano lies cm the right bank area of the river Ths area lies Between Sertumi and Ketkeio ana is 2 kms from Ketketo on ifl/gma Adhere high way going to Ketketo ii is near Ketxeto spnngs, 3 test prts nave neon dug m the area wmch indicate. Laboratory tests connucted on samples coliecieo from the Ot»se VM have rndicated
•ne following properties.
t. Grain sue distribution Sand
Fine
Gravel
2 Atteroerg Limits (%j
w.     Uquid Limits (LL)
v.      Plastic Linvts (Pl)
vi.      Plasticaty Index (PI)
4.2 Borrow Areas for Rock Fill Shell Material
Shell material
Not done
Not done
not done
62.9 %
<1.53%
21 32%
The remnant hills in the reservoir area and the remnant ridges downstream tut close to the ten abutment can be assessed for rode till material The size of the noge is quite targe and there wrll no! be quantity problem One exploratory borehole Labeled as ADQl was drilled to investigate the quality and quantity of lhe material. The toial volume of the material u depicted In Table 4 .2. The site has large material reserve designated as ADSHQ as shown on the map at Fig. 4 1
26
Water Works Design & SupervUiOD Enterprise
La UwdsUnn HU InitraitlrKiiul Consultants usd Techno crats Fn Ltd.Arjo Dedessa, Irrijatlon Project
Dun Appurtenant Works
May 2tXT7
Twq   areas  nave  been  identified  as  potential  source  for  obtaining  rock  matenar  (or  me  sneil  rone of the dam
The areas identified are
Sr
no
Village
Name
Easting
Northing
Elevation
GPS From
dam Axis
Distance
L
ADSHQ
242190
&43100
1354
3   km   aown   sveam   oi   dam axis on the left bank
d
Guche
2344B9
943400
12       km       down       stream distance of dam Axis
4X1 AD SH Q area
A© SH 0 area ■& located about 3.0 km on the downstream axis of dam and is on the let! bank of the river n is one km downstream of confluence of Wama nver and Dedessa River and upstream of stream Seyo whicn is a dry nver stream <_aooratory tests from this borrow areas have not been cameo out ou1 the characteristics of the rock and its properties are reported to be similar to the rocx pi drill holes AD, to ADj »no the rock found in the drill holes ADSt and ADSj at Saddle No-1 and Saddle No-2 respectively The average laboratory test results of drill notes ADt Io AD5 and AOSl ft ADS2 are given below
1.  Sound ness (%)
2.  Pdtht Load (Dry)
3.   SSD
4 Unconfined Compression test
4. U Guche Area
4.04
&30KN/m3
;            700 KN/m:
30375 Kt4fmz
Gvicne Me has also teen identified as a reserve site for shell maternal in case of requirement of additional quantity The Site it located ai the coordinates above mentioned ano at a distance of 12.0 km for the dam axis on the left side on the downstream
4.3     Quarry Sites for Rock Rip Rap
The  remnani  trachytic  plug  at  kole  are  of  the  command  area  can  be  exploited  for  construction np rap matertai The qua' rty for matenal is Investigated at CDSCo slaboratory Two sites have
_________________ ___________________________________________________ 21 Water Worts Design ti Supervision Enterprise
la JUwdxUOD InctrwBtlueiitiJ Cfla$Dlujitj and Technoenu Kn_ Ltd.Arjo Dedessa IrnjatJoo Project
Dam Appurtenant Works
MsyJtHT
own identified for quarry area for rock to be used tor rip-rap. These sites have Deen Known by the name Bukcto and Colsir Buketo B located about 6 km upstream of tne aam axis on the rigni side where as Cdlrstf is 26km far down stream from ine dam ax*s on the left Side The absolute location of this Site of cofiStr H at JTM 224160 m £, 946815m N and location o1 Buketo is 249320 m E ano 941079 m N and elevation at the foothill 1352 0 m. The laboratory tesls conducted Oh samples have instated the following average values Location of borehole CRQ 1/5 4 BRQ 1/2
Porosity (%.)
3.75
Unit weight (kg/m2j                 2751
Water absorption (%)
15
Specific gravity
2.74
Abrasion f%j
31.5
Sound ness (%)
2 59
4.4 Quarry Site for Coarse Aggregate
Roc* for coarse aggregate is identified ai uphill area ATE village on the way to Yanfa. The rock is jointed but only slightly weatherea, fine grained miffic basalt The center □( this row oji crop is at UTM 243582 m E. 934698 m IS and eltvaition 1473m It « wortamE for opening fhe quarry and suitable for coarse aggregates The site for coarse aggregate for concrete work Identified s designated as ADCAQl and Maribo and depicted on map at Fig 4 l
4.5  Sand
The Dedessa mer valley is the potenbal source for sand Sand deposit is observed close to the Dedessa bodge on Bedele- Arjo road and upstream (About 6 0 km from the branching off from Bedeie- Ago Road) through the nghl probable main canal line. Borche. Loko Sefera, LOko Bndge and Tuku Senbete has been identified as quarry sites for sand Tyllu Senbele t? located n the bed ol the river Dedessa, while the other two are located In the bed of tnbuianes Borche and Loko. The approximate distance of all the four sites from the dam axis is aoout 60 km Sana samples have Peen collected from the three sites Borche. Lokosefera and Loko Bridge
The  laboratory  test  conducted  on  samples  collected  from  these  areas  indicated  the  fotlowing values:-
1. Grain Site distribution:
Gravel :                       4.1%
Sand
87.5%
_______________________________________________________________________ ___________ __ 29
Water Works Design & Supervision Enterprise
b AunUOoo vtW laUmotliMiicil comtiuais and Technocrats m. Ltd.Arj o Dtd«m IrrtfaUu Project
Dim Appurtenant Works
2 Specific Gravity
3 Organic Content
4 umt weight
5 Relative Density
6 Effedtve shear stress
Miy 2W7
Fine
Loose
Field
Dense
cv
7 Effective angle or imemai faction a'
8 3%
2.55
1 6%
1261
1475
1485
0 67 kg/m1
3.5 KN/rn7
60.33°
4.6     AnalyaU   Toot   Results   of   Materials   for   Construction
4,6.1 Gradation of Clay Material
The samoies obtained from potential sources of clay material for construction of Inc dam nave peen tested m me laporatory ana nave indicated properties, which show large percentage of finer particles The gradation curve of clay materials for all borrow areas are shown m Figure 4.2 the soil samples report have indicated high values of liquid hmrt. wrncn Show that lhe clay soils ere highly compressible The values of properties of material contained m tne finai report of Construction Design Share Company in*cate very high value of shrinkage The average shrinkage vatue of 52.64 % is considered to be very high as compared to the recommenced value of 8-10%. The average value of free swell ts about 49.9 % for the all borrow sites tested, which is also nigh Nearly all of them plat beiow A-line signifying property of high plasticity Silt.
4.6  J Plasticity indea
The average LL values ata m general greainr than 50% signifying high plasticity properties The Pt values of day Irom cnewo arsa ere lower than from other source* The Plasticity chart for day samples from all borrow areas are shown in Figure 4.3.
4.6.3   Permeability
The coefficient of permeability of day samples from borrow areas is quite low t*n average of lO O* crrvsecj matting it c^iite aseaue and suitable as core matenal to mimmue seepage. Due to this property of material, woncaoildy problem in general could be expected. Th.s nowever can be overcome by making a test embankment prior io (he construction of the actual dam and assessing tne best way io conduct the compa ction wort,.
JO
Water Works Design & Supervision Enterprise
tn ±SWa*Uon with IntereoctineatU ConiulUjiis Lad Technocrats 1"tl Lid.Ano Dedtssa inn in» Project
Dam Apputtmoi Works
4.6.4  Dlsperslvity
May 2007
The gradation curve of the clay materia^ indicate ine materials co be very fine Fpr ine aery fine nays rftacenais from the barrow areas. ine dispersion tests were arranged co he conducted on the VYWDSE Soil tailing laMXarOfy Dy pm nole lest, and double n/Ciro meter tests as per the ASTL1 standard. The tests results revealed (hat the fine clays are not dispersive in narure.
4.6.5  Clasatfl catton of clay mlnerarogy
Far ths classification of clay mineralogy for dflCrtnl borrow areas, the plat al Plasticity Ihdfij w's cay sized partrcles (<0 0C2 mm} was made Wh.cn indicted that Ine clay classification is Kaolinite in borrow areas of Ale, CnewO where as it is Kaolmne hub Illite in character in case Ol Dhcndessa and Mariko bofTOw areas These are indicated in Figure 4 4
4.6.6  Swelling Property
Fgr assessing the swelling property rjt day materials (or different borrow arsas the plot of activity and the percent □( clay sizes From different borrow areas Indicate medium Lo mgn percentage (1 5 in 5? of swelling potential These are indicated ir Figure 4 5
Witsr Works Design 1 Superrtslon Enterprise
In suadaduwnh IntBmqtLnettUJ GflWUKUiU and Tbs bn writs Prt Ltd.--------- AIM TP? ---------------A1« TP?
~
--------MB TP $
TP5
D*«1 TP 10 --------- Me IP J —Me TP 4
ChB TP<
* 1 n TP ! 1
*TB TP ■                ATI IP ■ ATB TP  ■ W~ LTflJ TP fr
04 1P»
CMB TP 4
lX> IP 5             *-■ C*« TP 4 O»TPll™«—CKTPti
Qi« TPS
OHBTPir
MB TP y a MB TP 4
-- MS TP ft
-*-{XSTP3
0CK3C4
PERCENTAGE FINER (%JPLASTiClT* INDEX (PI) (%)
PLASTICITYCHART
Aline Uline
LLw=35
LLw=50
LLw=70
Llw-90
■ CHB
LIQUID IIMIT (LL) (%)
ARJO-DEOESSA IRRIGATION PROJECT Flfl.4 3 CLAY SAMPLE FROM CHE WO BORROWAfjo Dedeui JrrtfiUoo Project
Dam Appurtenant Works
Figure 4.4 ACTIVITY CHART
ARJO-OEDESSA IRRIGATION FEASIBILITY PROJECT CLASSIFICATION OF CLAY MlNEROLOGV
M*, 2*07
ALL BORROWS
% desized parols (O ^ ’
l 2 TuTl
-
1
34
Vater Worts Design & Supervision Enterprise
In AindiUon «1U LuamaUnuilal Conjulcinti and Tvduiocnu Pn Lid.AR JO DEDESSA IRRIGATION FEASIBILITY PROJFCT
TEST    CODUCTED    ON    CLAY    MATERIAL    FROM    ALL    BORROWS
CLASSIFICATION CHART FOR SWELLING POTENTIAL
CLAY ACTIVITY Versus PERCENT CLAY SIZES (FINER THAN 0 002mm)
0
20
70
PERCFNT CLAY SIZES—0-iOOBRCQf SAM3NO J
•- LOO6*OdC 5*N0 no i
LOO MF£ft* iANO NO J
100 3EFERA SAND NO 1
—♦- bqhcmji sjlho NO 2
—t— BMcma SAW MO 1
SAND GRADATION
ARJQ DE DESSA IRRIGATION PfiOJFCT
Fbg.4 fcSAND FROM At I SOURCES
PERCENTAGE FINER i%)Arjfl Uedeisi Irrlfitlm Project
Dam Appurtenant Works
4.7  Shen Material
May 2J07
From the lest results of ine shell material «t is observec lhal they are generally wreak in strength
The poind load tests conducted also indicate (830 kpuj me rock to ue of medium strength ciass
Since it is in abundant supply its use has been mace in the shell zone of the dam by accepting
wwer strength of me rock matenal. ano the dam stebon has peen desqned accordingly
4.8  Sand
4.6.1  Gradation curve af sand material
The gradation Curve plotting Tor tana samples from different borrow areas have been snown m figure 6 6 TM plotting indicate mat contents of Fines matenal in the sand samples collected from various identified borrow Hreas indicate very high percentage of fine material ifi the sand Sampte and this send matenal do not meet the litter entena far its use tor filter design. As Such coarser sand matenal is to identified lor use along with this or eise crushed material from the quarry may be used as admixture with the fine sandy material such that the admixture meets the filter design entena for using It for filtenng
4.9  Design of Fitter
4.9.1  General
The prospecting for suitable sand sources has been done dunng me geo-technical investigations in the project area. The prospecting nas concentrated on stream deposited sand locations of Borcne, Loko Sefre Law Bodge and Tullu Senbete areas The tests Oh sand material from these sources have been conducted at me CDSCO laboratory in Addis Ababa The full laooralary rest results are contained in the laboratory reports
The AgthDeoessa earth and rock fill dam has been provided with a central clay core matenal with upstream ano downstream finer and transitions. The transition material of intermediate gradation need to be provided between sand fitter ano the rockfill shell material both on the upstream and downstream One transition between the sand filter and the rock fill Shell has been proposed at this stage The sand fitter is proposed to act as dram and the 2 5 meter ihickness of a ana filter will also function as crack filler The rock fill shell material and transition matenal5 are to be obtained by Masting of the available volcanic rocks since these are only sultatse matenal available locally in the vicinity of the project area.
3?
Water Worfci € Superrlslon Enterprise
In Auatkaikm with iiitfwiwtiBMHi raimiit^mj and Tmtumcrati rrt rmArjoledHia IrricatiOQ Project
Dun Appurtenant Works
KIT MOT
The thicKnees of upstream and downstream fitters has oeen proposed io te 2 W m considering easy of construction and meetrng IM drainage capacity Further refinement of filter thickness may be considered at the detailed design stage
The graoanon of the naturally availatre sand material for use m fitter is also considered not Suitable as it contains large percentage of fine materials and >1 does not fit the designed fi'lei band, making it not surface for the purpose Further investigation of sudabc sand material tor jte as fitter need to be earned out during the derailed design stage. If d proves drfticult to Obtain suitable sand material for use m filler then crushing of available rock may be considered
4.9.2 Sand Filter Design
The filer to be used m earth ano rtwx fill dam should meet (ne twz basic function trf retention ano permeability
Id craer to retain the fine clay material in the central core erf the dam, the design of sand filter band ti« been aoopteo taxing into consKMfabori the fihenng. segregation, permeacifity Hna stanMy req^iremenr
The gradation curves of day materials from the different identified barrow areas exhibit ciayey matenals tn be very fine For very fine day base soils the filter design entena used here is based on laboratory study cameo cut by Dunningen. Tasbffl ano srwraro and
•     For Filtering. Maximum -
A«
< S but not less than Q.20 mm
■Mil*
From the filter provided
D,5(f) ■ 0 15 mm
Cutty ■ 0.02 mm
- o i*
D (fr) 0.02
u
*    For Permeability, Minimum > 4 but not less than 0 10 mm
^ISl
D,5f ■ 015 mm
D,j b ■ 0 003
___________________________________________________________________ JB
Water Works Design fc Supervision Enterprise
la iuoeUtlon with tniertOdltnmuJ Co militants IM TKbiMrtta Ptl Ltd.Mo-DtdMU irtlgauMi Project
Ditn Appurtenant Works
May 2007
ft J
■
c 35
<A .
-   — ■ $0 * 5
D.,b 0DQ3
The finer provitfcd meels the permeability criteria
»  The  allowaDW  fitter  design  pjnd  must  be  Kept  retativety  narrow  10  prevent  use  of  gap- graart filter The warned f.lber band range of particle size has Peen kept narrow
* The designed fitter banp must not hare exremety broad range Of particle Sliet w prevent jse oi possibty gap graded litter TM aspeci ia io w taken cane of during cofHtruct»n stage
*    Segregation of filter duhhg wruirjction shall be minimized For segregation erf filter during c-ons-lruction to be minimized
Dt&f ■ 0 07
Then maximum 0^ should be 20 mm In thug case
tW) rs less than 20 mtn and rS m order
■ Coefficient of Uniformity (Cui * -> 4 a_
□«(r
D,p(f>
■ 0.3 mm
= D.O7 mm
0.3
Ab(P
0.07
*4.
3 >4
thrs meets
me entena mat coefficient pt u
rwformity Tot fitter material should be more than 4
Coefficient
of curvature (Or) *
-- >1
EkjcjfO - o.z mm
CW^’OJO mm
DiD(b = 0.07 mm
CMflieeni curvature CV ■ —--------------
03x0.0?
(0 2}’
39
W»isr Worts Design 4 Supervision Enterprise
in MKtfaflnn wiffl line ram Un entil CudJXlIlMU ud TMhfidttilS Pit U4Irrlfitipa Pw]f n
DamAppurtenant Works
siiyao?
■_
0(M
'  4.021 w2>1
ana satisfies the criteria? the! coeffiuent nf curvature BhpuUd de more 1h»n i
The selected flier rand Tor clay material! propnsea tar uSO 13 a owe is provided at Table 4 2 The Mier band proposed rs made wwe* (0 accommodate wide range of filter material and tnown m figure 4 7
Title 4.2: Selected Design Sand Filter Sana
Sieve No.
r
w
Sieve opening 1mihj
25
9.5
IM4                                                  4 75
percentage Passing
100
90-100
85-100
NO 10
2
75-100
No 16
1.16
70-100
No 20
064
65-100
NO 30
0.6
50-100
No 40
0.42
40-100
NO 50
03
30-80
No 60
0.25
25-70
No 100
015
6-35
NO 20C
0.075
up to 5
4,9,3   Design of Transition Filter
Trar.&Hon fitter has been pravidec between IM land filter and the rock Lil shell material both pn the upstream and downsUeam pi mm filter The transition fitter ol 2 SO in thickness hag been provideo from consiaeralmn ol consiro titan convenience to tMl ■! *K1 10 m thickness erf transition filter A avtfabM CdhSrienng the iniermiKmg during construction of this filter material #iLri the adjoining materials during construction and compaction
40
Water Works Daslgn 1 Supervision Enterprise
tn. JUsodiCloa with IdUfcodUdanud CoaiuJluiLi nd Ttchnocrju Pvl LtdF’S 4 ♦Arji? Ut di-Fis, DrlfiUon Prefect
Dam Appurtenint Works
H»y2M7
The trjnrsrt+an filer material nas been designed to meeL the requiremenl of filtering and pernieaDihty the sjme way as has been acne ter oejign d sand1 filter materiel M meets Che laquttamMCs Besides Che filter matwW Mtbfy the ajcFfiCiem of umfomuly and mt
flr curvature requirement cnnsxtering ihese aspects the selected design fitter tend for Che transitidn li.ler material pfovidiea is given Cetew in Tape 4 3
Ta hl# 4, J Selected Design Th»a*<tten Fitter bank
Sex No
Stne opening (mm) l---------------- —
% age pining
B
!1
25
100
ND. 4
4 75
go-loo
Na W
2
75-100 —J
ho 16
■ i ia
65-100
f*te 20
QM
60-100
N<? 40
0.42
50*100
No. 50
0 30
45-100
Nd 10C
0 15
20-60
--------- —-----------
No. 2®
1
0C75
C.20
4!
Witer Worig Design ft Supantelui Enterprise
in JteuditioD mdi loumnuiienial Comultuti ind TEdmacnti Ptl LulAijo Dtdessi Irrlglttot) Project
DamAppurtenant Works
5 SEISMICITY
5.1  General
May 200?
The project lies in a zone of medium to low seismicity. The dam nas Deen designed lo De safe dnoer anticipated seismic loading condition Keeping in view the seismicity 1he design features like provision ol extra free traard wide and properly designed filters, flarmg of core at the abutment cqnisci area etc have been provided for
6 2 Seismicity of the Region
The Arjo-Deoessa dam Site is located in the weslem piateau of Ethiopia, outside ano far away from the Afar and mam Ethiopian rift, wtircn constitutes the northern pan of the African Rift valley However |he chance cannot be ruied out of (his dam srte area being nit by a damaging earthquake which may rupture m me rift valley.
Generally Afar ana the mjm Ethiopian rift are seismicalty active bui incomparable with what is along the Pacific Rim Earthquakes (hat nave occurred in (he region are reppneo tc cause relatively less loss of life and damages than equivalent size shocks tn other earthquake prone area This is not because they were nor destructive out is due to the then sparse population distribution and little development of infrastructure As the pace of urbanization ana infrastructure development pcka up in the country it ts prudent to consider the possible earthquake tnreats in the sub region. The Arjo-Dedessa cam srte w about 340 km away Tar from the 5.6 magnitude earthquake of 1987 m south-western Etniopra The other 6 4 magnitude earthquake of 1961 m Kara k<jre IS a iso very far away Figure 5.1 shows the earthquake Ideation in brack dots along Afar and the mam Ethiopian rifl white th* block star represent location of Dedessa dam site (Seismicity of Ethiopia from Ayde 2005 Earthquake catalogue p-otleo on 90 metre resolution Digrial Efevabon Model DEM) data.
The   two    earthquake   locations   are   hign   seismic   potential   areas   for   the   dam   sics   Afar   is generally sesmicaiiy active arid a damaging earthquake can occurs any bme
4)
Water Works Design 4 SupervUlou Eaterprise
tn Aisoetltlee wLlh LcLErtontlneiisi] Cautiluati and TecJtMCrttt Pn. Ltd.Arjo Dedttsi Irrigation Project
Dam Appurtenant Works
May 2007
Figure 6.1 SEISMICITY OF ETHIOPIA
36             37'            38*            39‘            40'             41‘            42'            <3 ’
Aytte, 2005 earthquake cmuogue (see annex: pkm.ee <xi cm  W  meters  rwtucion  DEM  (Digitti  Elcvibon  Modet)  data.  Bhiek  oau  are  earthquake  tocauon aaoAg Afar ana the mam Ethiopian nft ntoile the buck mn represent locatoces for Dedcssa 1 Gumeea dun sues
Water Works Design & Supervision EnterpriseArjo Dedessi Irrigation Project
Dtm Appurtenant Works
5.3 Design seismic Coefficients
Maj 2007
The earthquake force experienced by a structure depends on Ks own dynamic characteristics -n wdltion Co those of ground molion. Response Spedrym meirwd likes into KCOUnl these characteristics anp to reMmmended for use in case where it is desired to take such effects into
account  For  design  of  other  structures,  an  equrvatam  static  approacn  employing  use  01
seismic coefficient is adopted
5.4      Seismic Hazard Map of Ethiopia
A  reference  was  maoe  lo  Geophysical  observatory,  AddU  AO3O3  Unwerarty  Addis  Ababa Ethigp^ fpr MtomfC cdetficem r<j oe adopted for the design of tnt ATJCfDedessa Dam mealed in Jima  Area  In  (heir  report  cured  June  29.  2M6  they  have  enclosed  "SeitmiC  Hazard  Map  of Ethiopia  and  Hr  Northern  ano  Eastern  Neignbonng  Countries" The  hazard  is  tor  3  probSPilffy of occurrence af D OC 33 (Return per oo of 300 yearsj The conlfiunS io the Mamie h&zaro map indicate peak horizontal acze station as a iradicn of g. In Figure 5.2 for the Aryo-Dedeua 0am >i»  the  nearesL  contour  al  0.05  of  peax  nonzomal  acceleration  on  the  nazara  map  has  been snown Which IS considered lor Uw sta&tty analysis of the dam SSCtiMl. The srie is in an area Mtsnttauy at ton dangerous lo-caucm of me ccuniry but the possibility of damag-.ng earinquake from the adjacent nfl cannol be ruieo c-jt
Several attempts have wen made to produce seismic hazard map of Eltuopia The results «n
M nfiuenced by me limnitiow m aata both in quality al inslrumentatKin and time span cove.rao
The seismic hazard map of Elhiqpia from tfn available iftsWratedonic data is shewn in I he
above figure
5.5     Horizontal seismic coefficient
in the light of above the honzcmai seismic coefficient '* o of 0.05 g and vertical seismic coefficient h * 1t2 of v . a ■ 0.025 g has been wnjqered In the stability anatysis of dam section for Ajyo-Dedessa Dam Pnojeci Dynamic Analysis of the Otm section to not considered as the project area is ■, a zone of mett.um io low intensity.
Warn Works Dealgh &Sup<irTiKtoEL Enterprise
In Asweminb uiU lam ulknwtiJ Co nsul tuna md Tecta (mu brt Ltd.Arjo Dedejsi irrigation Project
Dam Appurtenant Works
11*7 2007
FIGURE 6-2 HAZARD MAP OF ETHIOPIA
46
WateT Works Design & Supervision Enterprise
In AmcUtion with lnterw ntlneouU Consuttxnu and Technocrats Pvt LULArJ DtdtSsl Irrigitioo Project
Dam Appiirtenitii Works
6 DAM HEIGHT
&.1 General
Maj 3007
The mam parameters that nave been considerea for deciding the height of the aam include, topography of the area, the geological and geoteenntcar set up of the fbunoation rock the fiver inflows. irrigation and other demands or water siltalicn iate m the reservoir ounng the active lite oi the reservoir and the evaporation losses in the reservoir The height of the Arjo-Deoessa dam has oeen considered after carrying out reservoir Operation studies considenng the vanous inputs.
6.2  A review of the previous studies made
The studies carried oul in the past reveal that USBR had considered a height of 7g Om for Aqo &eoessa Dam site DO-tl providing storage of 1059 0 Mm3 for meeting irrigation requirement pf 1&B50 ha and for generation of eiectncrty WAPCOS proposed a dam height of 00.0m ar a site 50 km upstream of ?i1e proposed by JSBR providing a storage of 705 11 Mlm’ exclusively for rm g afro n command of 1390OG ha BCEOM suggested 05.0 m h>gh dam with a storage of 2190 Mm1 for irrigation a command 0< 14280 ha at a location same as that praposea by USBR
6.3  The Present Dam Height
The present dam height cOnSKMfM now is of 40 6 m height above the river ted level at a location on rrver Odessa 1.5 Km upstream of confluence of River Dedessa and Warna River providing a storage of 1341.15 Mm at full reservoir lever of 1356 0 m for an irrigation command of about HJOO ha. and for generation of hydro electricity
The lave* of river bed at the dam srie a ar EL 1320.0 the aam height from 1he nverbea Is 40 6 m However the dam he»ght from the foundation wouio be about 43 6 m considering the depth of weathered rock in the river bed.
6.4  Free Board
The free board provided above Full Reservoir Level (FRlj ano Maximum Water Level (MWLj should be adequate enough to safeguard against overtopping of the dam unoer wave conditions The normai free board is computed at FRl and minimum free board above MWL The free board wris&h has given the highest requirement of TBl (Top of Bund level) IS finally adopted
1
47
Water Works Design & Supervision Enterprise
la Associate wtut latercoodfitoul Coutilcanu ud Techoocnts Pit Ltd.ArMetasi [mutton Pmject
Dam Appurtenant Works
The factor 1 hat are considered for the cstxnation of the tree board are -
aj Wave cnaractenstos wave height and wave length
b? Height of wind set jp above still water level adopted as free board reference
elevaton ano
O Slope of trie dam ana roughness of the pitching on the slope
6.4/ Method for Free Board Computation
Out of the available methods for free board computation assistance has been derived from T SaviHa s method wtncn is wdety used for free board calculations of embankment dams Free Doaro computations nave been mare as per the Indian stand vd (S'10635 ‘Guide lines for Free Board requirement in Embankment Dams ‘ This requires that Normal Free Board at FRL shall De cateulateo by adopting design wave height (Ho) as 1.67 times the significant wave height (Ms) and Normal Free Board snouW not be taken less (han 2.0m For calculating minimum freeboard al MWV half 10 Two (hud wind velocity is to be adopted As the region may experience higher wind veioatos dunryj the period water level in (he reservoir is al FuB Reservoir Level (FRLj, natf velocity has been considered for computing free hoard at MWL This free bosrd has Deen subjecl lo a rmnimun’. of 1.5 m The resign wave naight (Ho) is to be taken as 1 27 times the significant wave height (Hs).
6.4.2 Computation for Normal Free Board at FRL
The letch length is computed as the straignt-tne distance a«ng the wind direction over open waler on which wind Clows, which is marked lo cover the maximum reservoir water, spread area within 4S’ on either side of the fetch. There after the nfleetive (fflch (f,) is computed by the ten owing
Where Xi denotes (he length any radiai, wnich ts at an angle from the central radial The values of Xi are lead from the reservoir spread of the Arp- Deaesaa flam for different angles of the ratals I* is the effective fetch length. These are tabulated In Table 6.1.
Water Works Dulgn & StxpenWoD Enterprise
In liMcUtton wtth Intercontinental Consultants sod Tcchaomu Pn ltd.Aijo fiedessa Irrtfition Project
Dim Appurtenant Works
Table 6:1 Effective Fetch Length {f.JCompuUtiDn for Normet Free Board
May 2007
a
f
Xi Cos j COS a
CcsCr                    Xi
42            0 743
06                  0 33
36
30
0 809 1 55
0.866 5 45
1 01
409
24
0,914                        5.6
4 68
' 18
0 951                       81
7 33
12
0 978                        10.25             908
s              0.995
10.55             1044
0              1 DC                        13 77             13 77
6
12
0.995                       9 95               9 65
0 978                       6 95               6 65
19
D 851
3 70
3 35
24            D.914                       3 35
3b 0.066 2.7
36            0.809                       11
2.80
2 02
1 37
42           0.743                        15                  0 83
^Carn -13.512
VAYCaiaCojer = 78.32
71.31
13.513
3.79* bn
The data on wind speed has been obtained from National Meteorological Service Agency Audit Ab*D*, Ethiopia and has been used for caiculatrng of the wive herght. From the data the maximum wino speed in the project area observed 4$ 6.0 km/hour This for a 50 year return period has been computed to 30.0 km ffibut and thus wind velocity has been considered on the land surface m the design compulation
Wind velocity on water surface (V) ts computed by multiplying it with wind coefficient '{?' corresponding to effective (etch to the wind velocity on land (U) The wind coeffictenl 'CT for an effective fetch in urn (f.) of 5.8 fem ts given as 1.27 n the iS; 10635 code Therefore design wind velocity on land surface works to 1 57x30 ■ 36 1 kmrtir or 10 56 msec
,_____________________________________________________________________________________ 49 Witer Works Design & Supervision Enterprise
to AMOdabon with lnttnxmuncoui CcenMuu ud Teduxuna hrt Lul7
*rjo Ded«ssi irrigation Project
Dim Appurtenant Works
Significant wave (Hi) is compuied oy the relation as below g HsW  = 0.0026 i.g 4 )*"
r
For v=10 56m/S«C.
f. = 5800 m
rls = 0 555 m
Wave period (Ts) i$ computed by ine following relationship g Tsvv = 0 45(g. kw*)nT*
for  v  ■  10  Sa  m  sec and  f.  ■  5800 m
Ts = 2 78 seconds
Wove length (La) «s computed by the relationship
LS - 1 » Ti3
For Ts’ 2 7fi
:
Ls ■ 12.04 m
Design Wave hmgsht (Ho, ■» computed by |he refationsmp
HO = 1.67 Hi
For Hs* 0.554
Ho ■ 1 57 x 0.555
- 0 927 m
Wave steepness raw Ho/Ls <
12.04
■ 0.077
Relative run up R/Ho 1w embankment swpe of 3H:1V and H<j/Ls ■ 0.077 is read cm the grapn of wave run up ratio versus wave steepness and embankment srtpe and ts read as
R/Ho - 1.40
Where R is the run up. Therefore R - 1 *0 * 0.927
*1,298
Designed  ’Ra'  considering  dumped  stone  riprap  for  up  stream  prelection  is  computed  by multiplying 'Ra with the surface roughness CMfficieni
Surface run off co-efiicient (of dumped np rap is ■ 0.50
_________________________________________________________ __________________________ 50 Water Works Design & SuperTtslca Enterprise
la liMcliUaii with [niareontmtouil GonsnlLui 14 isdTnchaocrau ht LtlArjo-Dedssii IrrtgittoQ Project
Dam Appurtenant Works
Thetefore. Designed Ra ■ 0 5 x 1 290
= 0 649
M1JZW7
5
Since the wave sum on rough surface (Rh) works ChJt to Oe less than the designed wave heignt {ho/ Therefore Ra c kepi * no i.e 0.927m
The  average  »p<n  of  trie  reservoir  'D'm  m  nas  Been  worked  out  as  25.23m  Therefore  wma sei up ‘S' n m is compuiec by the relationship
Winfl sat up S • V  Ff62OOO D m
Where V ■ wino velocity in km/hoor ■= 30.0
F => Maximum Fetch tn km = 13 "7 km
□ = Average Depth of Reservoir in m = 25 23 m
Wind set up S =          38 1 x 13 77
62000 x 25.23
= 0.012 m
formal Free-ward required * Ra + S
-          0927 + 0012 m
=         0.939 m
This is less then 2 0 m
nonce Minimum Normal Free boara of 2.0 m at FRl snail be provided.
. Normal Free board provioeo ■ 2.0 m
6.4.3 Computation of Minimum free Beard at MWL
The fetch length rs computed as the straight tine distance along the wino direction over open water oti which wind Wows wmch is marked to cover the maximum reservoir water spread area Wtthm 450 on edher akw of the (etch. There after the effective fetch (fj is computed by the following
Cos a
Where Xi denoted the tength any radial, wmcn is at an angle from the central radial. The values ol £ are read from the reservoir spread of the Arys-Dedessa dam for different angles of the raOaisfor MWL at EL. 135B.6 m as Unrated below
51
Water Work* Design 4 Supervision EDurprtM
tn isudidon with laUttMtfaitDCaJ Caasultutt ud Tadueenu Pvt Lid.ArJJi tledttas IrrlffUJoaPtQjKl
DUH AppufttMDt ffctllS
Table 6.2: Effective Fetch Length (fj Com putltlOh far m inlmum Freeboard
May 2007
rp-
Xi Gan a Cot a
Cos a
X-
42
0 743
14
0.771
36
0 509
34
2225
30
0 856
56
4199
24
0.914
76
5 516
1a
0 951
011
7.326
n 12
0 978
10.2
9756
6
0 99$
1175
11 632
5
100
1395
13 950
fl
0 995
865
5.564
12
0.976
6.95
6.648
18
0.951
3.70
3.346
2a
0 914
3.40
2840
30
0 066
2.70
2 025
36
D.flOT
l.flfl
1276
42
0.743
1.45
fl.TBfl
£Ctua = 13.512                          £ Ar Cwa Cw - LB 872
Effects Fetch ft
Fetch Length 1396 km
. TD^rffGMfl
-------------  = —-----------
2, Cow                   13 532
it .(11
. ti.Oi?Jbh .tiT- 6.06
For MWL condition the wind spew on land is coniKfereo naif Of at FRL condition as per the IS code and this has been considered In the design com puts lion
Wktd velocity on watBr surface (VJ ft computed by multiplying rt with wind cceffoeni (? wneiponding |t> effects fetch (l^ lo the wind VttaClty on Lana flj) The Wind coefficient y for an effective feich in km or S.Q6 km 15 given as 117 as per the tS 10635 code Therefore, cfeiiflfi wlna velocity wi water surface wonts to W.O x 1J7- 19.05 km/hr a 5.29 m.'wc
Sigrwficifti wave (HJ is complied as btrtw
52
Water Woriu Design & Superrteloa Enterprise
lo liitHtiaDtio elfe Intern nUi;cotaJ Conoid lull and TfCUHtrtCa PtL LuL■ef2«7
1
Arjn-Dedtm                        Project
Pitn Appurtenant Works
ffHj/V - 0 0026 tg.4;'"’
V
v = 5- 23 rrVSCC
re = 6Q60m
Ms ■ o.272m
Wave pen Dd (Tsj is computed By ttw following relationship
g TaAf-tt«foWy’*
faf »■ 5.29 nuset *na fe = 6060 m
Ti" 2 07 jaconets
l
V'i a*e tengtri [Lsj is computed by the notation ship
U * 1 56 Ts3
For Ts = 2.07
-Ls ■ 6 .69 m
Design Wave height (Ho) is computed by me relationship
Ho ■■ 1.67 Ms
For Hs = 0.272 m
Ho = 1.67 k 0.272
= 0 454 m
0.45*1
Wave sleepoess ratio Ho/Ls ts computed
Wwri is * 0 068
6.69
Relative run up RiHo for emoarikmenl slope of 3h:1 and Ho/Ls = Q.OOS read on the graph of wave run op ratio versus wave steepness and embankment slope and is read as R/Hc ■ 1 43 where R rathe run up.
Therefore A_ = I 41zQ.4S4 m
= Q.S49 m
As  this  Is  more  than  Ho  therefore  value  ot  R«®  0.649  as  computed  has  been  considered  The average depth ’Dm' of reservoir in m has oeen worked out as 25.0m. Therefore wind set up ‘S'
v3f
m m » computM by the reHatiwishrp wind set up S =----------------- *D
62000 "
where v»wlnd velocity on wafer surface 15x1 27 = 19.05 kntfhr
F» Maximun letch tn km K 13.95
Dm ■ Average depth of reservoir in m ■ 25.0m
.. Wfrviset up
S3
Watnr Woriu Design & Supervision Bnterprise
In JdttCUUU? wfffl lDl*n»ttWtcl*J Umnlunu udTwtanmx Fn. Lid.Aria-Bait H* IrrifitLou Project
Dm> Appurtenaai Works
= 19.05 j 13 95 6.2-1 JDIJ * 35
= 0 003 m Free fioard Required = Ra * S
- 0 54& ■* 0 W3
■ 0 652m
May 2007
This free boarq compared is less than mt minimum free bo arc al MWL ang shall oe more lhan « equal to 1 5m Therefore lhe Minimum Free Board shall oe 1.5m Considering setoement dur Io aSrthquane of 0 5m the- free ooard provided above tor MWL 1 5 * 0 5m
• 2 DGm
The free mere ecmpuiabon for Normal Free Board ts given is Table 6.3
€.4.4 Miolmum Free Botrd at MWL
Minimum free board at MWL MS own eemputed in the same way AS Tor Free Bdflto for normal wat« wvel The fetch length (F) and effective fetch I'M rj calculated al MWL The wind velocity on land m this case has been considered naif of the ccmsriered for Normal Free Board computation. The COmputiHOn lor minimum freeboard are presented in Table &3. In case the mmimum freeboard computed is less than 1,5m then at Inst 1.5 m free bo a to is preumeo
6.4.5    Settlement Due to Earin quake
Since Free board comptrtSd JMvC dots not account for eflea of earthquake induced waves (seichesj seMlemeni of Mm and cam founaafron i-ience allowance nas been provided for these aspects fri (he free PMfrJ Fqr an earth and r<jck fill oam sett!emenrl of 0.5m is ebnsflereo in compul.-ng Ine freeboard for sartlemenl due to earChquaKe-mduced wives
Hence Freeboard provided above
if Full Reservoir Level (FRL;- z.O * 0.5 - 2.50 m
ir) M«imum water Level {MWLj 1 5+<f 5* 2.D0m
6.4.€ Top Bink Level
C&nwJermg the normal free board lhe top of dam weeks td EL t3 1355 + £,9*13565 and on oPASideriCzg the minimum free board above MWL lhe rap of Mm works to EL 1356 Wm ♦ 3 00
-  iMO.Gm.  It  n  seen  from  itMwethai  the  criteria  of  Mimmixm  free  ooard  above  MWL  becomes lhe  critena  tor  deeding  tee  top  of  dam  eevailoh,  which  came  r&  13W  6m  Therefore  Dam  c/esi has ceen Kept el EL 136Q.6m.
_ _________________________________________________________________________________________  S4 Wttar Works Design & Supervision Enterprise
|n AiBorianon Witt iMfittOutlmeiltt] GddUlltUIJ Ud TKtUHCHU Pn LuLArjo DedM!( JrrtgaUon Prtjert
Dam Appurteit&at Works
Reservoir Operation
Hl!2*^
The  following  control  levels  are  requires  for  reservoir  operation  for  fixing  me  maximum  live siorage of reservoir during the useful life of the oam and required freeboard
(i) Full Reservoir Level (FRL)
(nJ Minimum Draw Down Level (MDDL)
mil Maximum Water Leve (MWL-
6.4.7  Full Reservoir Level
The mam objective <s to achieve maximum live storage from the available annual river flows in a monsoon period after meeting lhe irngal on demand in the command The water over ano above the irrigation demand is stored in the reservoir for meeting fne requirements during a oryflean year and for generation of hydroeiectnc power However the site topography, geological consideration ana safety aspects are the lirtuling factors tar lhe height of (he oam. Hente cons«denng these aspects the top of the dam has been fixeo al El. 1360.60 m
6.4.8  Minimum Draw Down Level (MDDL;
The  following  consideration  nave  been  kept  m  v«w  lor  fixing  minimum  draw  down  level (MDDL).
(i) The lunction of mgation outlet Is noi affected due to the sedimentation of ti >e useful life of the reservoir
(ill  Adequate  depth  of  water  above  the  irrigation  ouflei  is  provided  to  prevent  any  vortex formation when drawing waler from the irrigation outlet
Keeping  the  above  aspects  the  minmurn  draw  down  level  (MDDlj  m  the  reservoir  has  peen
fixed  at  EL  1350.0  m.  The  storage  in  the  reservoir  at
FRL  =  1341.16  Mm   The  active  storage
3
In the reservoir between FRL at 1356.0m and MDDl st 1350.0 m ts 466.49 Mm1 at the Sian of operation The dead storage has beer [brad at EL 1350.0m and the storage at Dead storage leno is 674 67 Mm3 With the active life of the dam considered for 100 year the sedimentation In the reserve*- wouKJ attain a level pf EL 1330.67 m ano the active storage In the reservoir *wto be adequate erwugn m meeting the mgabon demands. In add.non io meeting the irrigation demand for water the surplus water in lhe reservoir could be irtitaed for generglion of power as a secondary source for generation of revenue These aspects may be examined in greater details at the time of preparation of detailed project report.
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Water Warks Design & Supervision Enterprise
In Auetildan with IntcrttuUncstaJ ComuJuhu and T«hnocrats PtL Ltd.ArJtUkdwsa Irrtfinoa Project
Dam Appurtenant Works
6.4.9 Control Level
T.riE variola control levels ol Arjo-DedesM Dam ana reservoir are glutei« under (i) Arjo-Deoessa Dam
Maj 2007
Length o< Dam
Rrveroed level
Top otDam
Hrnghl erf Dam above ftve<S beo Haight ot Dam awvt deepest foundation
(ai) Reservoir
Hasrmum water leva (MWLi Hl
Full reservoir ievei (FRl Minimum Draw Down Level (MDDL,
Deaa storage Mm’
Live storage Mm’
512dm
EL 1320 CO m
EL: t360 6Qm
<0 6 <n
*3 8 m
EL. l35S&tlm
EL 135B0m
EL fSMLDlri
$74.7 Mm1
46fi 40 Mm’
5<r
WiUr Warks D eslgn & Supervision Enterprise
Lt Lssoditto2 will kncreooLinentil Consul LauLs in5 Tctkn-acnCs PTL Ltd.Arjo Dedessi Irrigation Project
Dim Appunenant Works
Table 6: 3 Free Soard Compulations
Frae board Computation ^according to 1$ l0635:l993|i Normal Free Board {it FSL} a hail be > Im
Minimum Free Board i.at MWL) stiall be > t.5m Full Reservoir Level (FRL) 13-56.0© m
Ut* Slope Ol Dam 2.5H:1V
Ma; 2007
s. Nd
Step-wise computation
Normal Free board
Minimum       Free Board at MWL
Remarks
1 Fetch >ength (F) in Km 13 77 1395
2         Effective Fetch (le) »n km                                               5 80                     8.08
3 Wind ^elbcity Ova* and (U) in km/h 30 00 15.00
4         uVlrxd Coefficient I.Qi                                                     1 266                   1.27
5 WWW velocity Over water surface (v) in km/h 38.10 19.05
6         WM velocity over water surface (v) in rTvs                   10 58                   529
7         Stgrwficam wave height (hs) in m
0.555
0.272
8 Whvc period (Ts? in seconds 278 2 07
9 Wave lengtn (ts) In m 1204 6 69
10 Design Wave height (Ha) In m
11       Wave steepness Hofl.s
0.927
U077
0454
0 060
12       Relative Run-Up R/Ha from diagram                              1 40
13 Run-up on smooth surface R in m 1290 0.64S
14       Designed  Ra  wn&ioenng  dumped  pitching  for U/S Slope protection (R x 0.50)
Since  Ra  worts  oul  to  be  icss  tnan  designed
wave Wight (Ho), Ra * kept ■ Ho ■ 0 927m                    0 649 IS       Average Reservoir Deplh (D) In m                                  2523
0.325
25.00
Ji's slope
- 2.5H:1V
Since ha
ra less
than Ho,
■.value ol
16       Wind sel-up in m
0.008
0 003                        Ht>-0 927
17       Free beard Requited m m                                                0935                   0652
ie        Permissible Free board
19 Top of dam (as calculated)
2.00                     1.50
1358.00 1360 1
has been
adopted
20       Top ol cam required. considering settlement               1358.50               1360.6
21        Top of d»m woprec. m
EL 1360.6
______________________________________________________________________________________ 57 Water Works Design t Supervision Enterprise
la Anadabaa with lnurai nUaemaJ Co nsultams ud Tec turn era is Pit. Ltd.AijaTtdrssa Jm^aUon Ptaject
Paid Appurtnui Warks
7 DESIGN ASPECTS
7.1   General
H*y ZGfli
The   design   of   earth   and   rock   fiH   embankment   asm   would   be   gpirernec   by   the   fbH&wihg considerations
■     The  dam  materials  should  hive  suff-denl  shear  slrenglh  Sfl  Wai  the  requirement  ot  Staftihly under various static condition and earthquake condrtrcin to which the dam and its loundaliOh is subjected shouM be met
*      The  OESign  flexibility  should  be  suffi&ertl  tb  tfcw  the  Fullest  possible  uijluation  qt  all required excavation and readily available borrow materials
' The core maienaL in 10 be sufficiently impermeatM to mill seepage through the dam and there Shall be a general increase in permeability from The core 1CW*d the extenor slopes or the aam
*       Fitter   requirements   between   adtacWit   JOWS   ano   between   the   tpunOatiqn   fill   msreriars IhQirtd be satisfied ■! order W avoid migration O< fine materials into coarser ones
■       The   transihon   zones   should   be   thick   enough   to   accommodate   si   conceivable   Fault mowiants
The earth «ng rock fill dem section ad spied is a conventional section consisting o1 impervious day core matenal ana protected by thick finer iranvUpnj on pie upstream, downstream and shell Of rack fill material. This es considered to be the appropriate dam type for the ArjO- Deoessa Dam Project due to suitable topography sng waiLdbiirfy of construdidh matenals for the oam in the vicinity el the area The upstream cofferdam is proposed <Q be incorporated imo the main dam section.
7.1,1         Embankment Features
7.111 Crest Width
The general cmtderabOrt lb adopting crest width depends upon the working space required aL lop of dam and also on the functional purpose the dam serves kke the public high wfty and requirement of Future needs
aj Ttw WKfl dam at crest as per IS 8526 - 1S7B 'Gm* iihM for design of large earth and rock nil dams' Should be fixed icootding To the working Space required al top and the crest width should not be less than S.-D m
___________________________________________ ___________________________________________ _ Witar Wprks Design & Stipends! do Enurprlatt
ll JdlPCUtfoa Vtlk lutcrwadnentiJ Ca Mail mu ud 1 mtmaenu FM Ltd.
15ArjDUtdtHi Irrigation Project
taua Appurtenant Works
b) According |g USSR 'Design of small dams the crest wdth iq be adopted m CSM rf small earth dams is grvon by
Mi? 20C7
F=y + ICh1(
where.
W = uvidirt of cwt m ft
H ■ rleignr pf dam in feel abort nuer bed. this in case of Atjo-Dedetta
Dam = 40 0 m
« 36.0 ft
OT ■ lOSBm
Say >1 o m
c)  US  army  manual  ’Earth  EmDannmen'  EM  T110-2JO0  3l"  July  T994  provides  that  top  width of an aarth and rot*.  <in dam, depending upon me height pf dam, the mwiimum tdp width should bt Between 25 ft (7 62 and ad ft (12 135 m).
Keeping in view Che above conscJcralions. Lhe Cop width Of OKI fot Aqo-Dedttsa Cam hes bean arotrtW K 10.0 m. The oam omt detain eresnown in drawing No AD-F-DAM?}3
7.1.1.2    Berm*
Berns snail be provided for serving lhe fc'lowing purpose
*    For providing Urtl surface for wmstmctiOn and maintenance of Che dam seclon
- Ftjr reducing lhe surface Erosion in case of dovynsveam stope and bfUtdng lh# Continuity ar
lhe slope
*    To protect tne l&wer eoge of the rtp rap and for preventing it thorn undermining in case of the upstream slope
Benns  o'  width  5.0  mhave  been  provided  at  every  vertical  eievalon  of  10  0  m  A  berm  60  m wioe at lop ewvaticn Of rock loe been pwidM
___________________________________________________________________ SQ
Wafer Wcu±£ Design & SupanhloD Eaferprlst
la AssndiUns with Id Ctrcunuita tu Cnmultuns Ud TcCbmmCi PVL. Ltd.fcjo-Detem internon Pmjen
Dam Appunmnani Works
_
_____________ ltajZMT7_
M. 1.3 Camber
Major portion of earth ana cock fin dam cnnsnliaaliQn lanes place during lhe ponMructon period Therefor a camber snail oe prcwiqeo along me crest of an eartn ana cock fin dam to ensure that the free board provided is nol reduced due to foundation settlement or consolidation of an earth ano rock Ml oam Therefore camber shall be prow fled awng the axis ol the oam from aero height at me abutments to maximum at the central section of the earfn and roO fill dam. Observation on existing rock fill dam indicate tnat settlements ranging from 0.2 % to 1 0 % of the dam he<gnt nave been experienced For Ar|t>-Dedessa Dam a camber of 0.5 m has been provflM at me maximum section lot settlement purpose
7.1.1.4   Para pal Wall
A parapet wall of i 5 m height over arfl above the free board requirements has been provided as an aoditonai safety The reservoir face of the parapet wal i has been provided win a parabolic curvature so mat the splashes resulting from reservoir waves if any are returned Pack to me reservoir
7.1.1.5  Guard Stone*
Guard stones of Size 300mm x 300 x 750mm has been provided in cemeni concrete Moots
1 3.6 at spacing of 3.0 m centra to centre on the downstream edge of top width of dam.
7,2    Design Parameter
■) Free board
k) Properties of Materials
iii) Seismic Coeffi&ent
The above design perameler has been described at paras 4.4 5 12 eno 11 5 respectively
7.3              Design requirement
The basic requirements m the design or Arjo-Dedessa Dam is to achieve safety with economy under various conditions of operatons of the reservoir The cntena adopied for the design of and earth and rocx Ml dam u given as under ■
•) Safety against overtopping ol dam during inflow design flood
b)   Stability of slopes
c)    Safety of dam against Aiemai eresfln
Mt
Viter Worts De dpi & Supervision Enterprise
in laaodaUon with Lute™ d Use a Lal Coned Lan la mJ lacluintTsti nt UttArfeDedtm IrrtgiUon Project
Daoi Appurtenant Works
7.3.1 Safety against overtopping
M>JF 2M7
Ta ensure safety agamst overTOpping adequate sprfhvay capacity has been provided to prevtrw Overtopping of the eadh ano rock fill aam during and after construction The tree ward provided IS sufficient 10 prevent overtopping oy waves and shall also la*e into consmerabon the settlement Of the dam a no foundation
7.3.1.1   Fret Board
The free ooaro has been calculated by *T Savetie s" method, wnich is widely used for free
board computation of earth and roc* fill dams The details of procedure and computations- nave been carried out according to Indian stanqara IS 10635 1993 "Guide lines for Free board requirement in embankment dam " and the computation for free board for FRl and MWL are contained in Chapter - 4 of this rtpod
7.3.2   Embankment Section
The dam section has been mamty divided mto zones namety the central impervious core and the graded shell material -of roc* fill!gravelly tenace material. Besides, the coarse and fine filter have been proposed at both upstream and downstream face of the impervious core Rip rap has been proposed on upstream slope face of the dam aoove the snell material with a filter underneath the roc* np rap Hand placed stones have been proposed on the downstream face of the dam io provide protection sgaimi erosion resulting from ramfall or wno
7.3.3   Zoning of Dam Section
A Summary of the required malwiai types m different zones of the dam section is given bdow in Tawe 7 1
6l
Wafer Works Design & Supurrtsion Enterprise
In IssocLidn n wtth LntorccnLLnraJlal ConsultuiLs ud TcchuncmLs Pvt LttLJkj'-Detteau [rrlgatioD Project
Dim Appurtenant Works
Hay 2K7
Tibia 7.1: Zoning of Dam Section - Materlaf Types
Zone No
Deception
Material type
1
Impervious core
Clayey material
1A
Coffer dam
Clay, son as for zone 1
2
Firw  filter  u/s & d/s face ol core
Sind,   filter   5   mm   maximum   size   and   silt   content (< 0 075 mm) *e$s then 5%
3A
TransBion zone
Small roc* fill 75 mm maximum size
30
Transition zone
Same as al 3A
«■
Coarse fillet
coarse sands gravel upto 75 mm size and silt 15%
4A
Upstream mil
Rock  f  II  400  mm  rnaxenum  Size  50%  maximum  finer tnan 25 mm
40
Downsneam shell
Rock  fin  500  mm  maximum  size  50%  maximum  finer than 25 mm
5
Dumped Rock np rap
Maximum size lOOOmm 40 IO. 50% * 000mm 50 ip. 60% > 3OO-0OOmm. 0-10%. > 300 mm sand. <«k Oust <
5%
'5
Blanket beiow u/t rip rap
Crushed rock or natural gravel martnum size BO mm
17“
_________
Hand placed rock np rap
Rock fragments
1
To preven: piping of (he fine traOicn of the core, a transition zone rS proposed A fine finer consisting of sand (zone 2) is provided downstream of the core A transition filter (zone 30) is proposed downstream of fine filter to collect the seepage through the core and convey it to the base of the downstream aha* of the dam A transition zone consisting of smaB fOCh flu may atso Pe required to be provide size compatiMfty between ma transition filter ano the large racx fi'l sizes ol the Shen at the detailed design stage
62
Water Works Dealer) & SupervtslQD Enterprise
In azudahCD with tulamnUnmUl Caisultiati and Tretaocrtu Pn 111Arjfl Beflessi lirlficlDn Project
Dun Appunenui Witries
Maj 2007
Filtcr layer (zone 2A a^d 2BJ are provideo Io separate core from the upstream she! amt downstream The Me titter (ions 2Aj adjacent to the core on the urs side wilt acl as a crack filler for any craCkS. wnicn might form m ihe core res jltmg from differential settlements
The proposer) zoning system is aimed ar maximizing the use of material obtained from ihe required excavation The weathered rock obtained from excavation would be placed ad|acwt to th* inner pan of Ihe aownsiream shell (zone 4A} while Hie sound unweathered rock would be ptacec adiacem TO the coarse fitter (zone 3A. 3B) ana toward Ihe Outer part of the shell
A separate rec* fid zone (zone 4j is proposed at the case of downstream shell to prcwije adequate draina ge capacity This rocx fill zone ft constructed using the more resisla-nj oasaflic rock
Th* jpslream face of the dam has Deen zoned (zone 5) Io prefect it from the erosion effect of the wave acron, Which will also impart drain ability in the event of instantaneous build up o1 pore pressure jnaer earth quake condition Rip rap material will M outlined 53 over size from excavation of basalt rock. The zonrig of upstream coffer dam wll oe similar Io mam dam The earth and rockfilt dim section rias been snown in Drawing No AOF’DAM/04
7.3,4   Impervious Clay Core
Th* compacted impervious o»y core provides an impermeable Darner within the body of the dam. Impervious days avaMabw locally are very suitable for 1hc core However, ciays neving fwgh compressiMity and bquid bmit lend to swell and are prone to hydraulic fracturing of clay core. Cuy soils having organic content are e«o not to oe used as core material
A central crxe ts preferred over the inclined core as it has the advantage ot poviding higher pressures at the contact between Ihe core ano foundation and reduce the possibility of leakage and pping. Since the avaitobilty of Impervious day core malenai locally a not a constraint at site, a thicker core cf compacted day with upstream and downstream slopes of 0 Sviv h» been provided for resisting the piping action The top eievabDn, of the nay core has been kept 1.0 metre above the maxirman water level to prevem seepage due to capillary syphoning The mrrwnum lop width of Dore of 5.0 fn has Deen prcvioed as per Indian Standards.
_______________________________________________________________________________ 61
Water Works tkslfn Supsrrtilon Enterprise
In Association with IntczctmlinonLAJ Cons’dllttttj tod Tethoocrau Fix Ltd.Vjo EMtsia Imfatiua Project
Dani Appurtenant Works
7.3.5    Shalt Zonofi
MIX 2OT7
The function of sheh is IO impart statxMy anq protect the impervious core The roc* fin materials. Wrnch are not subjecttM to cracking on direct exposure to atmosphere are Suitable Tor use as shell material in Aryo-Dedessa Dam tocaHy available rock material is made use of in the shell zones both in upsiream and downstream of impervious day care The rock material shall m hare, sound ana durable so as to rMtsl excessive break down during the handling and placing operations Dust and smaller fragments of rock shall noi oe more than 10% The angular bulky rocks are pretends as against flat. eiongated rocks or rounded ooulaers H rounded cobbles or boulders are used lhey should be scattered throughoirt the rock fill and not concentrated m pockets.
7.4      Foundation Treatment
7.4.1   Core Seating Treatment
The stripping oelow core seating win be done by removing lhe alluvium tai os and loose deposits The foundation for lhe impervious core, upstream filter ano downstream fitter will be excavated through me upper weathered rock to fresh rock, whirn can take up the grout Suitable core foundation shall oe eased co suosurfaoe geo-lecrmicai oats and shall be otnemec. from the geo-technical investigation. team The depth of excavation requited 10 ocnai n a surtabtc core foundation shall be estimated based on the assessment of the geo-technicai engineer J geowgist and the long.ludma, profile along me central line of dam axis indicate the depth up to Which the core trench excavation snail be done
The core *f» filter zone foundation surface should be thoroughly cleaned using mccnanireo equipment and high-pressure air water jets Open iomts ano minor shear zones will be excavated sna cleaned to a mmlnnxn depth of three times the opening width and should be seated by filling with slush grout back fill concrete. Io case some major discontmuflBWsnear zone* are encountered then these wcuto require special treaiment AJI depressions in lhe area pf core fbundalion ana filer foundation wW be filled wtth dental concrete treatment to provide an even and unerodabis surface and core material Shan be placed and compacted
tn the rnrtm of getting irregular iocs surface. 50 mm ■ 75 mm of shotcrete thickness over the foundation surface supporting the core and Oh both upstream pnd downstream filter has been provided This mat of shot crate will serve as a grout cap for blanket grouting operations
SUnxet grout.ng nas been provided to a depth of ID Cl m under the core and filter zones and
__________________________________________________________________________________ W Water WtjrkB Design t SupervlBlon Enterprise
ID JLuodstloD with laUnsotteeaul CemJtesu ud Teehn-scrtu Pn Ltd.Arjo Bedew* IrrtjitlciD Project
Dam Appurtenant Works
1172007
snail  be  based  on  lhe  sub  surface  geo-technical  information  and  sampling  obtained  from  the fleM   invesitgaiion   conducted   by   uVWDSE   and   tests   conducted   on   samples   by   the   sub- contfacior    M'S    Construction    Design    Share    Company    (CDSCOJ    Addis    Ababa,    Ethiopia Consolidation grouting has been pfavioed to reduce the potential flow through open joints m the vicirwty  of  core  and  filter  and  thus  minimize  tne  potential  for  erosion  of  core  material  at  rts contact  with  the  foundation  Upsiream  and  downstream  fitter  zones  enveloping  the  core  nave been  provided  to  serve  additional  security  against  core  erosion  The  graui  curtain  comprising of  two  rows  of  grout  notes  is  considered  appropriate  on  the  basis  of  the  available  data  in  the valley  area  and  single  grout  curtain  in  the  abutment  area  The  spacing  of  the  grout  hole  has been provided at 3 0 m centre to centre Final spacing will depeno on the grout intake and test notes and win be determined dunng actual grouting operations.
7-4.2 Shell Foundation Treatment
Foundation excavation unoer the shell zone will oc required to reacn foundation materials having snear strength and compressibilrty al least comparable to those of the compacted rock rill. Talus deposit ana soils like weathered racM snalli oe removed, Bnd founded on moderately weathered rock along the abutment side slopes
In the nver channel area, all alluvium deposits will be excavated and the shell zone will be founded on competent, moderately weathered rook Where shear zones filled with p<pat*e materials uh«rfce the dowraPeam shell rt snail be excavatBd and a Fitter will be paced ewer
these zones io prevent piping. Before
ths first layer of material in lhe nver valley
lhe foundation msterlii wfl be thoroughly compacted by grvwig appropriate number of passes of a ■nbraiQQ roller after applying moisture to the reqmrea e xtent
7.4.1    Cutoff Trench
Cut  off  trench  shall  be  pfOvlow  at  the  Foundation  of  the  impervious  day  core  and  serve  the purpose given as under
•      To  reduce  the  seepage  of  water  resulting  from  impoundment  of  water  in  the  reservoir through Fchjodafton and abutments water faces with impervious core ana
•     To prevent the Sub surface erosion by piping
65
Water Works Design & Superrtfilon Enterprise
Id AHMUfijaa nth luun»DLlB«iui CtramJluti *nfl 1 actino-trait Prt Lid.Lr]o Dtdeua lntgsuoB Project
DwAptmrtemt Worka
fay 2007
1
A positive cm off shall be provided along the am of hie dam few the full lengln of the dam taking into consideration the geological set up of dam foundation and abuiment as revealed by the bore hoie logs drilled on the left ano nghl. vaUey bank and the fiver bed
The valley at the dam site has an over burden of 3 Q m lo 5 0 m depin conSrShng of alluvia - deposits comprising of silty clay intermixed with gravel matenal The positive dll off shall be provioeo up ic gromatwe rock to prevem any seepage from the reservoir at the water lace win impervious core
Based on the geotecnnicai investigations of tne cam foundation ana abutment area and the permeaoilily vaiues. consolidation grouting shall De provided m the cut oft trench area The pattern of grouting will depend upon me permeability of the foundation strata. The groui Curtains snail be provided to depths depending upon the geowgical set up of the foundation roc* ana rts permeability The grout hu«M shall be covered with b concrete cap
The bottom wdth of the cutoff trench nas oeen provided for full width ol the impervious core as. th* availability of core malarial is not a constraint The side slope ol the cutoff trench has been xept as Irt: 1V
After excavation of the cut off trench the same shall oe filled back wilh impervious clay core material and shall be compacted to optimum dry density The compaction shall be done with moisture content of 2% plus dt minus to provide an impervious stratum n the foundation.
7,4.4    Location of Cut off Tranch
a)  The  location  of  cutoff  trench  plays  a  significant  rare  in  reducing  Seepage  pressures  ana for  the  structural  stability  of  the  clay  core.  The  cut  off  trench  can  be  placed  on  the upstream   face   just   after   me   upstream   toe   of   impervious   core.   This   minimizes   the seepage pressures but ft e more liable to rupture if there ere small movements or partial failure   of   upstream   face   of   the   embankment.   It   also   reduces   the   resistance   of foundation   in   general   the   impervious   soils   have   low   shear   strength   (frictional)   ana therefore its nxabon in this sone is not considered favourable.
bj The cut off trench coinciding with the centre line of embankment, rt will have less effect in reducing seepage pressure through the embankment bur it wil oe less Irabw to rupture and less likely TO weaken the foundation
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Water Warks Design & Supervision Enterprise
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Dam Appurtenant Worts
tlu ZOO?
c)  A  cut  ofl  trench  placed  on  downstream  side  just  before  aownslream  we  of  rare,  has  no advantage  and  IS  aangerous  because  it  allows  the  transmission  of  seepage  pressure  in lit ger part of file foundation and reduces trie stability of the downsneam half o1 Lhe dam
In M<ew o' abd'/e merits and dements of aoove «ocanons it is proposed to locate [he centre line of lhe dam coincide with the centre line of the cut off trench This location of lhe cul of trench provides satisfactory performance as per the experience and has been adopted
7.4,5     Curtain grouting
Pressure grouting 01 rock foundation «s normally cameo out to fill discontinuities cavriies or votes in rco. mass oy suitable material The grouting aims at satisfying (he design iequ iiemenls economically and in. conformity with the rest of construction schedule
Curtain grouting is earned out mamiy to achieve conditions for saw oesigrr of lhe dam
(a) To reduce the seepage through lhe dam foundation.
(b) To reduce toe erosion potential ol seepage and safe guard the foundation against
erodib*ty hazard
(C) To strengthen the dam foundation and reduce settlement in the foundation
On both the abutment ana along the axis of the oam as revealed by the geo*ogical setup, the rocks appear n«jnty fractured and joirned sconacious and of veeicutar basalt type with poor
core  recovery  It  <3  therefore  considered  necessary  that  in  ordci  to  minutiae  the  nsk  04
seepage screw the dam axis, abutment and foundation, consolidation and curtain grouting shall be requued to be earned out. below core and fitter seating ano lhe abutment. This shat! be carried out through the grout horns drived from the cut off trench. Curtain growing has been provided in lhe valley reach in me cm off trench consisting of two rows of grout curtain ano single row of grout curiam in the abutment depending upon foundation contMions and permeability of the strata and geo-technical set up forming the foundation of the dam Consolidation grouting shall be provided m the cul off trench along the axis of dam by drilling grout holes up lo 10.0 m depth
7.5     Stability of the earth and rptk fill flam Section
An earth ano rock fill dam shall be sate and stable during all phases of construction and operation of the reservoir Hence me analysis has been done l&r tne most critical ccmbmaiion
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of  etfernai  forces,  which  are  iikaty  l&  occur  in  practice  The  following  conditions  are  usually criljca i for the stability of an earth ana rocx fill aam
a) Case I - Construction condition wrth or without partial pool
(tor upstream ano Downstream slopes).
dj Case rj - Reservoir partial pool (for upsiream slope).
c)         Case MJ - Sudden drawdown (for upstream slope,
d)          Case IV - Sleatly seepage (for downstream 5<ope)
Case V - Steady seepage with sustained rainfall (for
downstream s*dpe, (where annual rainfall is 200
cm Of more), and
f)   Case   W   -   Earthquake   condition   (for   upstream   and
downstream stopes.
The various design conditions ol analysis for upstream and oownslream stope along with the minimum values of factors of safety to be aimed at ano use of type of shear strength for each condition oi analysis has been provided This is given in Apperwfix-A of the IS code No 789a -1975 wnich is reproduced in Table 7 2
Water Works Design 4Superrbrlnn Enterprise
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DajnAppuneaa□[ Works
ItaytW
Table 7.2: Minimum Desired Values of Factors of Safety and Type of Shear Strength
for Various Loading Conditions
Minimum
Case
iMo
fading Condition Qi  Dam
1
Stope Mos1
Likely to be
Cnbcat
Type of Shear
Strength Test to
be Adoptee
Desired
Factoi d
Safety
1
Construction     condition     wilh     or without partial pool*
j
Jpsveam and downsiream upstream
16
II
Reservoir partial poet
Upstream
rs;
13
Hi
Sudden draw down
a)     Maximum     rwao     water     to minimum
with tail waler at maximum
0) Maximum Oil water io minimum with reservoir full
upslream Downstream
rs;
rs;
13
1.3
IV
Sleady seepage with reservoir full
Downstream
rs:
1.5
V
Steady    seepage    with    sustained rainfall
Downstream
as:
1.3
VI
Earth Quake condition a; Sleady seepage
bj Reservoir lull
Downstream upstream
rs:
RSI
1 o§
1 D§
"Where the reservoir is likely to be fiilad immediately after completion of the dam. construction pore pressure would not have dissipated and these should be taken into consideration
T This is to be adopted lor taduft plane passing through
impervious fouhdatxjn layer
; s lest may be adopted only m cases where the material a
cohesion less ano free draining
§ Values are according to IS: 1893-1975 "Cntena Tor earthquake
resistant design of structures (third reunion)*.
69
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The  uarious  lypes  of  shear  bests  performed  under  different  conditions  of  loading  and  drainage are designated oy letters Q, R and S as follows
Cl test Unconsolidated grained test.
H test Consolidated undrained lew, and
S test Qonsolrdaltd drained test
The cam 13 located m an area of medium to low seismicity and therefore psuedo static anarysis nas been earned out with earthquake condition IS 1893 ■ 1904 out. lines the procedure lor evaluating the seismic coefficient ano depend upon me shear wave velocity the height of the dam and lhe lowew paint o( lhe cam foundation through wnich the failure circle >5 supposed IQ pass
Arjo-Dedessa dam site e iocsIM m western plateau of Ethiopia and is far away from lhe Alar and the mam Ethiopian rift The na^ard map of Ethiopia and i1s northern ano eastern PCighOonng countnes for a probability d exceedence of 0.0033 indicate a honMfW seismic coefficient ah of aooul OOSg. (As per the report of Geophysical observatory Addis Ababa untversiry Ethiopia; The vertical seisms Coefficient is generally taken as half of a A 1 e a v ■ 0 02S g and the same nas been considered m slaWtity analysis of dam
7.6      Safety Against Internal Erosion
7.6.1    Seepage Control Measures and Drainage Arrangement
Seepage ttnerot measures has Peen provided lo protect the dam from any uhdes iraote effect ol seepage occurring through the dam body Of Ihrougn lhe foundation ana aouiments Drainage system has been so devised as to tackle the problem of seepage and or rmgratlon of fine partuses through the body of lhe dam or foundation. The design ts governed by the type of case material, hetfllw ol water in the reservoir and topographical features oi 00m srte The following arrangement has been provided
-     impervious day core
-     Indined fitter upstream of clay core
-     Transition finer downstream pf clay core
-     Homonrai fitter
-     Toe Drain
Impervious elay corei This has been described at: 7 3 4
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7.5.2    Inclined Flrt&r
M*y2W7
incHrwd niter is prowdad on downstream face sf impervious day core 10 coiieci wai« coming Out of the corg resuming from seepage and lherety Keeping lhe downstream Shell relguvely dry The filter on the upstream Face oi impervious core acta as crack filter The Mat should de Cleaned and well gradeo The minimum thic*«SJ Of filter rt Determined from considerations or
fi) The thickness o( niter should have artowance for iniermuimg with the adjoining zones The allowance than dc varying depending on compaction equipment used rtw Ine purpose
ft Minimum  width required fa* compaction depending upon the equipment deployed
(■in) Earth quake effects
Consxtenng the atm* aspects # minimum erf 2.50 m Ihtckfwss of each layer of Mer has bean provided horn working polroi of view The top eevition of the FiHet has been sc.epi at the same #evt« ai 1h*i erf the impemeus we elevation at EL 135& 5 The Filter material provided is free draining ano well graded as far as possible ano it shall not generally nave size greater tTian 75 mm so as to minimize segregation ouring placement The filler material provided has to satisfy the following requnremencs
ai It shouw be more previous than the protected base material ic act as an efledrre drain
0) The gradation should be such that the panicles of base material oo not migrate througn or
clog the filter vo«3S
c) It showM be of ihittness sufficiem to provide good distribution
FJtef materia should satisfy me sranMrd entena with the base maieriai as laid down in Irvdian standard line base soils.
Two basic functions of Filters ana drains tn earth and roc* fill dams are
i) Reterrfiort luncbon
iij Fltteration function
rne clflSM Tragi PttWl ^<4 addresses ^>4 addresses lhe permeability
wprinmni
The fflwihg, lagreflalion, pernwab! iy stability requirement) naw brtn considered m the
resign nt und filter bam 10 rete.n the fine Ctey maienal tn lhe core The filter design entena
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lo luocteUttiTUh liHmanttetttti Cwnlluti and T«4n»crata PtL LilArJo Dedessa Irrigation Project
Dim Appurtenant Worts
adopted   Here   is   based   on   an   extensive   istoraiory   study   camea   ant   by   JL   sherero.   lP Dunnigan and JR Talbot
As seen from tne jradatran curve Fig Nq 4 2 the
material loenlified is very fine. The
case day core material consists of very fine &ilts a-no clays and are more lhan 65% finer For vary firve ciay base material the following criteria nave bean used in the design of sand
filter
. Frjr filtering Maximum — — f 9 tout r»ol l»M IMn 0 2 mm
D n*
*    For Fermeablrty Minima J^'-- ' < « ^ul not less lhan 0 1 mm
AW
- The eilpwapte filter desngn band must tw Kept relatively n a<TOw (0 pcevenl usfr of gap graded filters
*    The designed filter bend must not nave ifi extremely broad rang* or particles s>zes LO
prevent use of gap graded fitters
» Segregation of filter aunng confiittaOf' snail O? minimum
The grain see curve of the filar fMv*MQ is nearly parallel Io that of the base material
Following crtlena snouid be SeUSfied for wct| graded Sana Peng used in the filler
(J)  Cn-eflicient  of  Uniformity ijDuj =■ — >  1
Ai
'[/} t3
(ii) Co-efTraent of Curvature (Cv) =----------- - — > S
AA
It  should  not  contam  SrVy  organic  materiel  end  the  parbcKS  betOw  0.075mm  more  than  5%  by weight
7.6.2.1 Compaction of Fitter
The tompftCtKO of Und in the filter should he dent Dy plate vibratory rollers lit I specific density rt achieved The relative density (RD) of sand after compaction shauid equal lo qr more lhan TO*.
Ln order to ottatn the desired density with mintmum rampaaing efforts, sand may be placed in dry or in saturated condrtxm. In lhe CMt of inclined sand filters lhe sand should no I be allowed to flow Out pl specified width on either soes during compaction It sfwultf be confined
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in betwcer two sheets Of plaiteS ihSialleO on either Sides nf the fitter, in order te ensure the specified width of the fitter and 10 avoid Mnteminalteri of fitter due to mining wrlh adjoining material
in order to maintain the prescribed siope or inclination of the filter during me cunstructjon. the impervious core hearting ZOfle ffluSl always be at mgher level than me level Of lhe tiller ano th* down Stream Casing zone must W kept 3t a tevei wh*cn « ■ UH rawer [nan ttte level ot the filler
Ttfit process should be continued m the same fashion fill the end of season *t the end Of
Which. the filter Would be kept *1 toast 1$ cm above IIM adrci nmg zones CO avoid contamination
oi soil with the Filer during rainy season
It muse also be enlurM with Jimos! Mte mat tfie material near the lunction Of Titter »nd (he adjoining zones on either sides of rt is compacted to the eppuiateo densities of (he respearve zones.
7.6.3   Horizontal Filter
The homontsl filter has been provided on stopped ground level downstream o1 the impervious corertransflion zone and has been connected with inclined fitter downstream of impervious clay Ctn A minimum snipe pf 1 m 100 has been provraea towards the toe dram for quick disposal ot seepage water The fitter material Shall satisfy fite filter cnflena T^ugn the thickness of twnzcnni filler required « small but for practical consideration a thickness of 1 5m has tieen prowled. The horizontal fitter has been provided tn coiled seepage from the foundation and the filter and minimizes possibility of pqtmg arang the aam Mat.
7,7 Safety of slope*
7.7-1 Upstream Slop* Protection
Dumped rock nprap by far is the most preferaoi* and adopted type ct protection for the upstream slope, it ha the advantage that the energy dissipation of IM wave u achieved as the wave naes and hence wave run up on the dumpfcl pflcteng is much less B compared io wave run up Oh smooth hand placed pitching or concrete asphah caching The requirement of hand placed roc* rip rsp ter the wme Wive height IS a do jt 1 2 td 1.5 times more than Chat ot dumped rock np rap due lq smoolher surface. However pra«mem of <0Cfc np rap would require wnsKJeraticn of economic aspects.
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Dajd Appurtenant Works
Hiy 2007
For the Ago Dedessa Dam. dumped rock np rap of 1000mm thickness has been provided over a filter thickness layer oi 500 mm Thukness of rock np rap have Deen computed taking in to account fi) wart tueigm (uj Emoankmenl slope (■) Weignt of average sue of rock
(rv) Rw specific gravity
A well-graded roc* nprap will exert less pressure and stress on the filler
7.7.2 The rock for rip rap
The roc* np rap shall De hard dense ano durable and shall De resistant to weathering and wave pounding It Should not crumble on long exposure to waier frost and air It consists of boulders of basted rock fragments Frfter below rock np ^P have been provided to prevent wart* action from eroding erf the underlying embankment material by the suction efled
7 7 3 The Dumped rock np rap thickness
The rock Size generally provided is given oelow in tabular form
The  flumped  rock  np  rap  should  nave  the  following  characteristics  of  dumped  stone or  rock fragments
i) Quality of rack
■) weight or sue Of individual pieces
w} Thickness of rock np rap
ivj Shape of rock fragments or stones
v) Effective nes ano stability of finer on which np np in p’-aced
5e no.
Maximum Wave                Minimum             Average Height in (m)                     rock size D 50 In mm
Minimum       rock       rip rap thickness |mm]
1
0- 1.5
300
600
2
1 5 - 30
400
750
3
3.0 and above
700
1000
For Arjo Deoesw Dam |he minimum thickness of dumped rock rip rap provided is of 1000 mm sue considering the quality of roc* rip rap available in the area
7.7.4     Placing of Rock Rip rap
The roc* np rap need not be compacted but sha ll be placed to grade in a manner to ensure Dial the larger reck fragments are uniformly distributed and the smaller rock fragments serve to fill
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Dam Appurtenant Warks________________ May 2OT?_
tbt spaces tietween trie larger rack tragmems in such a manner as will resuH m well Keyed
densely placed, uniform layer of np rap of specified thickness Hand p*acmg will be required
Only to lhe extent necessary 10 secure trie results above
In the placement of rock np rap care is taken to prevent segregation wttich court result m erosion of areas wnere small stones are concentrated or m washing ol beodmg materia, through packets of large Slones ft is also necessary to provide a blanket of graded gravei underneatn the np rap to guard against the danger of finer particles being suckCd Out of voids The np rap nas been emended 1 5 m below MDDL. The np cap accordingly for upstream slope has been provided Irom crest elevation Of 1360.6m to 1340 5m
7.7.5    Upstream slope of cofferdam
The upstream slope of the cofferdam is also exposed to the wave action during the rwer diversion and has Deen protected by providing I 5m thick layer of waste material from roc*, quany
The cntena of minimum rock size implies that the np rap should oe composed of rock naff of which sue should be larger than the recommended Dm size for a given height The rock should be weir graded from a maximum size of above 1 5 times the average size varying down to 2.5 cm spells to fill the voids between rock and to provide a reasonable degree of protection to the underlying filler layer The normal size of roc* 'D' <3 determined assuming the rock fragments to have a volume between that of sphere ana a cube or
Where. r-unit weight of stones in kg/m1
and W - wergni of Stone in kg consrtenng r - 2100 kg/mJ
[> 0 08 w,Q
On  rhe  above  basts  the  thickness  ano  gradation  of  tumped  rock  np  rap  for  Ajia-Dedessa  dam
proposed to be adopted are as below
I
Thickness of dumped rock rip rap ■
1000 mm
II
Maximum aize of stones
■
2000 kg or 1000 mm
40% to 50% greater than
1000 kg or BOO mm
50% to 60% for
-
45* 100 kg or 300 mm
upto 10% lew man
45 kg or 300 mm.
Sand end rock dim to oe less than 5% toy weight of the (oral rock np rap material
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7.8 Stability Analysis
7.8.1 Factor of safety method
May 1007
Different metn&as have Deen developed for computing factor of safety SLOPE/W and SEEPW software Developed by GEOSLOPE mlemationa* (Canadaj for analyzing factor of safety uses different methods ana all these methods are based on emit EquAbnum Formulation except finale element method
The General Unwt EquiMxium GLE formufet»on is cased on two factors of safety equations ana atows for a range of mtersbees shear-Normai force assumptions One equation gives factor of safety with respect to moment equiibrtum (Fm), while the other equation gives the factor of safety with respect to nonzortt# force equittxium (Ff) The General Limit Equilibrium (GLE) method satisfies both moment and force equilibrium by finding the cross over points of the (Fmj and Fr curves The GLE method encompasses all other methods regardless of slip circle shape GtE method in SlOPE/W can accommodate a wide range of differem interstice forces functions & AM the methods are characterized more by the equations of static satisfied and the manner is which the mtersbees forces handled than by the shape of the slip surface
The software analyses targe number of slip circles based on the methodology developed by Fellenius, Btshop. Janou, Spenser GlE, Morgenstern - Pnce Corps of engineers, tower Karafiatn. Sanna and gives the mmimum factor of safety for the critical failure surface The method aeveiopea by Morgenstern - Pnce considers both for the horizontal force equibbnum (F ) and moment equiiibnum (Fmj for grvmg the mewnum factory of safety His method is
r
considered  preferable  as  the  moment  equilibrium  on  individual  slice  is  used  to  calculate interstice shear force
Stability analysis has been earned using SLOPE/W ano SEEP/W software As regards staNrty of siopes of the aam body although earthquake loading is cyclic loading and has dynamic loading effect, lor the feas*>ilrty study report of Arjo-Dedessa Dam, only pseudo static analysis has been earned out by taking the horizontal seismic coefficient value a A ■ 0.05g Vertical coefficient a v is taken as hart of the value of horizontal seismic coefficient which works to be 0 025g These values of seismic coefficient have been adopted from the "Seismic Hazard Map of Ethiopia and rts Northern and Eastern neignbonng countries'
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7 8 2 Steady State Condition
Dawnjireem Slope
Hiyzw
Sla^ il) analyso for lhe downstream Slope oi Arp-Dede&sa Date under steady *UW WMUJitipn till teen done by consOtring furI reservoir level (FRL| and ftp water level on Iht dOTamjIream side or the dam cclh for With and without earth quane loading condition
Upsiream siope
The  upstream  jJqpe  staulrty  under  steady  SI81&  condition  has  teen  cheded  for  Mtn  under Normal c-ondnon and with earthquake wading condition
7.8.1   Conairuction condition
On completion of construction &1 emwnKmend dam ttw port pTVHUV 4 partially tfissrpaiM The reMuai pore pressure depends upon me compaefron methods and lhe morsiirt content during construction period and oepends upon me rate pf raising of the oam The residual port waler pressure is based on the pore water pressure ratio 'Ru' Which is given oy
LU Ru yl Hj
Were = loUi und v#igm
Hs ■ the height of the sod column
The values of 'flu' vanes for 0.1 Io 0.6 In the presanl case the value of 'Ru considered is 0.4 for analysis
7 J.4 Sudden Draw Dawn Cahdttlon
For the stability analysts of upstream slope of the Ai)0 ■ Deoessa dam the critical condition is sudden draw OPwfl tOndmcn and the same has been cons.geren The Factor of safety depends upon the rats Of rjajipenre of pore water pressure and the ute at wh.cn the draw down ures place from the Ml reservoir WrveJ condition to minimum draw down condition ny the discharging capacity liking pace wer the spiltway and of me *ngatiort outlet Swm the wngatior out iti dacharge IS hmrfed. the draw down taking pace Mlow the full retention Jeve* 01 dam at f 356.0m Id MDDL level Of 1360.0 will be lldw with Pte Oiwhirgihg capacity of bgfh the migabon ouwet, being atHJirt 17.0 m’rsec
7.9 Properties of Materials
The following properties pf the day materials have bren adopteo as resign parameter based on me lest result? of day materials from different bonow areas conducted m the CDSCO laboratory. There values have been considered for stability analysis of the dam section
-______________________________________________________________________________ 77
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DunAppunotuut Works
Miy 2007
Table 7.1: Properties of The d«ign parameter for the clay core
Properties
Unh
Core Material
..
*1
7 sat {Ma«t Unit Wetgrit)
Khwn7
IB 6
2
r iub (SuDmeroed uM Wagrrt)
KN/m3
3
r mrjtsl (M0151 Unit Weight)
KN/m1-
IB 4
4
Total cohesion C
KN/m1-
M
Is
total angle of internal friction
Degree
26
6
Eledrve cohesion C
KN/m3-
0
7
Effective Angle of fnctiQrt <P
Degree
M
Titrte 7.4: Rock Design Perimeter
Sho
Property
Unit                                   VMim
1
Sneii Material
Krum
21
2
Angie or intern^ fncjion
Degree
38
__________________________________ _____________ _ ____________________________ U Water Works Design & Sup errislrm Enterprise
Ln isaadallDn with InuroafiUBmEal n—iiiBfli i_ni
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FIGURE 7.1 DAM SECTION STABILITY UPSTREAM SLOPE
LkB
GaevdrtitiJi WVO CO. EN llJOvn
Arfo
« D«m
Anafy-w*
OwrfiKri
Up>wia»m 51004 Dffrvrftown
I
HMtNAgRl
w1# EQ
[Wripw E.ia m AM-i
V
W1 «IWJ
CMll XTrM* K' IWM i
MMiU 0 J
[>w>qpe-3" flay
MiKiai tataniCauBCHHfc
k«w i«<
C<0^MKA fi
Plw .Bl
Dwwwonc: n m I'
Nfa.W Ma*>C ■■ Jiimiji
W ’•*
Cah#wn *
Pr- W
btarwr«<i< Uo* 1
M-i--'" 4
UwnBnn LBS I Or9 tt-sHUi
bUwi MrwCaU&nli
wi ji
O
P*- 14
PMiXcmeirH: Lbw 1
B
Cwhu n*«yi CehtBunRi
'44 JI
Ctfmuri ii
rwv M
I'taziwTwiiw 1 ™ I
Ml4M A> I H
[>Kipo* fhKHoci M«M HMkia-fa
t-^f^TwIir t
•'
55
•
1W
iMOt
sV
t
n 4l<
79
— 
le r Worts
i
"" ,. -
._ *.................... ... I*—*"-"Atjft Dedfl<i&i Jtrtgtil do Project
Dam Apgurltnajit Works
Maj 2007
FIGURE 7.Z DAM SECTION STABILITY ANALVSI&OF QAM SLOPE
»  r. nthlMo vl..Q .aru hm.
Wt
Ar jo L't.j* i ■■ D«rn
An>t ^f
p
Up#njtm 3J-W DHwDflwn 3**1 r EO
<• • •
Lira Skip*- QPD Condition W<iO EQ. ELv IMO
WM4.               1
OMcr^fton A/aia*
WrdV MaS»«n^h
w*m a*or
P<j« ««w, ►’ i pva t
«!»•••*■ J
□«■ • •<>..<! Car,
M Mr.A-rt*
L
M If 4
C^*M»n 5
R* M
RftflBMWftac LH« *
Maa^^a >
CMac»«<A-*« Ci*,
Mall* We~Cv^^b
■6" 114
S-
Ph Ml
Pmr^fimkr^ 1
Ual«. *B 4
Oau-W UrtlACySQxUA w.-tM, lAariCo _k9<va
-M 21
Cur**** 0
•5
Dvacnflon C -sAadwr* Mode* Wo*vCc^vH> Wt 2-1
Co*Mcn D
PH 1ft
Pwjnwwtoc l tfta *
aAawttfft ft
C3m<>rfa»<v> ftetpia.a Wr-w ftadKKv
DlltlOtt (Rl)
sii
Waler Worts Design & Supervision EnterpriseAil a Dedessa Irrigation Project
Dam Appurtenant Works
FIGURE 7.3 DAM SECTION STABILITY ANALYSIS - DOWN STREAM SLOPE
May 2007
Df®
Slala W® EQ
Arjo D*d**«> D*m
Oowriflroarfi Slope SdMdy $l*t* EQ
*i
BbwvBwh T-M®
■Yl "■«
l
H-V K
r UriAAHAi a** *
Ml»*< J
wa» *■ P 5
CMaairtpM* uvfl II 2-*
Mrf Ji
Pw M
FwfwtwBiT. LM »
I
Mb«!F a • ”
[>*< «*•■**" P-F-i
1*3.41    H»-»4X.b
■afefcc <*4> ij,BOweFi^»
UBKWl 4
E8CT5%'”’ '
IWUMI
.'/■■rin^tar Mi Mfr-
wi J>4
I £■** **<■*•■
WWH UasrCsairwr^
“i-S- Nk-HlflOf*
I
Cwm" i
■* > JI
a
a¥ I ■ I
0w M
•■*■•*. i  i
n
Mbi M
• •••• 
• ••♦ 
• •Ar] & Dcttessa lntgidon Ftuj ect
Dun AppurttinatiL Works
Tatjlf 7.5 Stability Analysis ■ U p»treim Sl&prt
Miy2D07
Condition of inatysia          Circle        touching election
Minimum FOS is
per IS code
Minimum FOS as per
stability analysis done
—
Upstreim Slope
a} Swjden Draw Dowr 1320.0 b) Steady state 13300
i) WjUloul EQ              13*06 i) V/rtn EQ                     1330.0
T.3
1.3
1 462
1430
15 1              1 560
14W
1
TO
jpiirMtn Slop* stability AnaiyiEj
UpsH&am Slope 2H IV from trust uptQ 13*0 6 m and 25M tv Qpwn words up !o EL. 1320 Qm
FRL EL 1356 00m
MDDL EL 1350 Odm
Tatite 7.4 Stability Analysis - Downstream Slop* Downstream Slope Stability Analysis
Down stream 1.SH IV
FRL EL 1356.0m
Ctmdftlon of anatytbl          Circle         touching elevation
Minimum    FOS    as per IS code
Minimum FOS as per
•lability inatyal* dome
DwnSiresm Slope
a) Steady state                  1320 0                       1 5
Without EG
tij SttMy state
WfrwutEQ
1325 0                       1.0
1.6*3
1.517
* FOS Factor of Safety
•     EQ : Earthquake
________________ __ _____________________________________________________ S3 Waler Works Design & Superrislon Enterprise
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Dam Appunenant Works
itay2OT7^
From the above Tables 7.5 S 76 it re seen mat ine factor of safety of upstream slope under Supden Draw Down conation is very dose to the minimum factor of safeiy as prescnbeo in IS COOS Showing that Ine upstream sigpe adopted for the dam section is safe
For the downsiream stope jnoer sleady state condition the factor of safety both for without Earthquake and with Earthquane situation, the factor of safety is very <po$e to the minimum factor of safety as proved in m*an starwaru code sngwmg there Dy that the downsiream slopes adopted are sate
The stability Analysts of the dam section lorvanous loading conddHjns have been done using Geo-studio 2004 soft ware and these are shown in Figures 7 1 to 7 4
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Dam Appurtetiant Works
3    RIVER DIVERSION
HM 2KJ7
For protecting the wart ano during OCKBi ccn&l.ucnon in the twd <rf a ruJIuripH river fl d obligatory To rscHafle Irre firtf rows away from me worn place This is required so that the warning area remains dry or semi dry The method and arrangement of diversion work depend prmanly jpon tne cross section Of 1he valley the 1ype of aam. diversion discharge ano 1he bed mare r-a i m tw ftvW
The design flood tor fiver ounng the construction period to mfluthCW mostly by the risk ana damage factors involved in lhe diversion arrangements, tfi CMfl trf a rill dam the nek of overturning of enroankmend durmg construction may result in S&npus damage to wbrxs partially wmptftM This tonSiwration may not oe so far a COWOIO dam where flood water may over top the partly constructed dam with ffltle adverse e fleer If the appurtenant structure permits.
F<x Atja-Dedessa Dam wti<n is a large oam, the river d were ran flood of 100 years return perrod
4    Cflnsiaered  osira&e  as  per  .ndian  standard  code  14015  2WO  and  lhe  same  should  be adopted  for  nver  diversion  wwts  wflh  Suitable  prareci.an  measures  taken  al  the  eno  01
CbnstfirCton  season  for  cop  arm  oownstream  of  embankment  dam  to  pass  Surplus  flo* constoenng the possibility ap lhe flnoo exceeding Lhe design diversion. flood
However far Aqo-Dedessa dam 100 year return pehM rOutK flow nas by the hydrology group computed and tor over diversion diMing conMfUCtMh T*Olt 10 1 Rmw design flood computaLans al cofferdam made tar nver diversion during construction through a tunnel. As the tjnnri arrangement far rwer diversion ra oat considered. pvtn bvret OuCI of 15 m K 3.6 h Size wtlh rqu'vatecii area ol cross Motion m^sec has been provided Wfln COfTCfdam CDp kept at El 1340.60 m and wrth freeware of t 5 m provided
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Dim Appuricuapi Works
Table     8.1     Routed     Design     Flood     forRiVd     Dlvertlon
Return period 100 year pe?k discharge 671 m3rsec
May 2007
D (mj               Q n/feei:
Etevabdrt ^masE)
50
2tS
1338 89
5.5                   232
1334 05
6 0 353
1
1331 15
e.5
277
1329 32
LHftflCh Of p«pe LMWm
H River Divenion Arrangements
The nver diversion arrangement during construction have been considered by construction of a wfler oam on the upstream sioe at 2D.0 m httgrit wnich would ultimately form an integral part of the mam eadn and lock fill dam and a Dft Cd her dam SO m away tram Wie EL'S of me dsm and annul 8 Om high to provide ma* mg area free fro waler Art RCC Cum <JuC1 of sue 3.5 m w*de m 3.5 m high woud oe consnucted qn me righi abutment The riverbed levs is st EL 1320 0 m Therefore in order tn prevent sill entering the duct the invert level at the duct nas been provided at EL, 1322 0mP i.e 2 0m wove the rrvertied Layout plan of the Rcc Duct and jt-SSCUOnjI Midi are Shown in drawing Vo AD-F-DiAM?3Q 3 31
Dunng Che lean partM Of 1ST year whe-n mt discharge in the rtver bed is very tow, the excavation of fne cut off trench upto design ieve= m the left anutment reach for a length of 125.0 rn (Hl o m to 338.0 mj ano ng nr auLlmeni for □ ength of 19Q.D m (From fliZO.D m to 720.0 ffl) involving i totai length of 225 D m s proposed to be done. Consolidation grouting providing concrete cap Ofi the gr&ut bote topi and Panic filing of trench is to be taken up simLittanewsry with this th« excovabon. Simuhanenusly the construction of the RCC twin barret duct, 1tS construction end competton « to be down The site warante for the cut off trench, shell zone and construction of the rock fill dam portion upto EL l340.fi u to tn? achieved Site clearance on the upstream of the dam axis up(t IM of the am. rwlng the main coffWn which s jUimatety to form the integral part of the mam dam upw EL 1340.6 aiang with upstream protection works is to be completed
-------------------------------------------------------------------------- ------------------------------------------ 85 Water Worke Design L SuperrUioa Enterprise
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Datn Appurtenui Wks
Mm 2007
In the- 2nd year wont on the downstream for site Clearance core filters, horizontal fitter rock loe and downstream shell may also be taken up after construction of hie above, the routed flood discharge of 100 year return period wmcn equal 215.0 m-rsec snail oe diverted through the completed twin barret box dud
In the year of working season period remaining works, relating to consolidation grouting, grouting, cops, filter ano shell reach arc to oe taxen up and the normal raising oi me earth ano rock fill O*v impervious core, fitter upto maxmum possible elevation feasible should be done
During a* year the balance works of Curtain grouting and raising up of the dam upto design heigrtf. providing root np rap on the upstream slope, construction of wave waN. D/S drainage and protection of slope are to be completed ^ower of duct gates and pegging by pumping concrete and grouting of the plug simultaneously This actually is lo performed m the iast three montn of lne working reason after the dam construdron 4 completed upto crest level
Spillway structure ano facilities in saddle ADSl tne work on the spillway structure spillway fatalities Irrigation outlet and intake structure in saddle ASDi for Right Bank canal and the Saddle dam are all moepenoenl and the construction of these doe* not interfere with other components of the wort. These as such shall be taken up Simultaneously from the very start of the construction worts of mam cam
The construction work for the mgafion out lei and n$ intake structure for the left Bank main Canal likewise is to be taken up independently along with oilier works From the start of the project
ft
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Dim Appurtenant Works
SAUENT FEATURES
Ml? 2007
The Degessa River. flowing northwest is an important tributary of River Apbay ft origmaies from Mf venmo and Mt A ache ranges and Bows in an easterly direction for about 75 km Thereafter it turns rather sharps to the north until fl reaches the Abeay River The Arjo-
□edessa  project  command  area  is  largely  rotated  downstream  of  this  sharp  turn  The prefect envisages the construction of an earth and rock fill dam, chute spillway facilities located m a saddle No 1 An irrigation oullef with an intake structure in a sadd'e No 2 on the right flank for the Rrgntt Bank Primary Canal and an irrigation out lei with an intake on the left abutment far Left Bank Pnmary Canal taking off from a left bank aoutmcrit of the dam. Other features of the left  abutment  outlet  works  are  an  upstream  pressure  conduit,  a  gait  chamber  ana  a  RCC conduit discnargmg m a basin from where the left bank primary can» lakes off at a distance away from the aownsueam roe line of the earth and rock fid dam
The pro.Kt envisages imgabon m a command area of >3,665 hectares The project is planned for Irrigation ano generation of nydropower The saltern leaiure Of spinway faculties and imgslipn outlets are oesenbeo as foltows.
Type Of Dam
Location
Maximum heignt
Oam Crew width
earth & Rockfill Dam with ctmrai
impervious cere
Latitude 8**31*12" N
Longrtude 36°-4O’-04* E
i) 40 6 m above river two
il) 43.6 m from the deepest foundation
loom
lengtn of crest
512.0 m
WWtn of Dam (mai)
ItW.tJ m
Top Etevrton of Dam
EL 1360.60 m
Upstream Slope
2H. 1V from crest to E L 1340.6 m arw
2.5H:1V
Downstream slopes
1.5H:1V Upto EL 1320.0 m
(7
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Dam Appurtenant Works
Spillway (<J rested)
LOCkUon
Rijnt Bank Saddle No-J
Type of Spinway
jngated Ogee type
a) Design flood return period
1 in 10.DOO yrs
b; Peax inflow discharge
1965 m’/s
Spillway outflow routed discharge
USSOm’rs
Crest revet
EL 1356.0 m
Wdtn rrf spillway crest
125 0 m
Max surcharge lift over crrat
2 62 m
Reservoir
Catchment area
Max. length
Surface area at FRL
Surface area bi MWL
Max Waler Level
Normal wwer Lever
Minimum Draw Dawn Level(MDDL)
River Bed Level
Reservoir Capacity
5278 0 sq. Km
41.0 Km
87 85 ion2 ai M .W L,
96 01 Km7
EL 1358.80 m
EL  1356.0  m
EL  1350.0  m
EL 1320 0 m
a.
Al Max W.L,
1580 3 Mm’
b.
Al Normal W.L.
1341.20 Mm3
C.
AtM.D.D.L.
874.7 Mm3
Out let Works
Lift Bank Primary Canal
Location
Left Bank abutment
Discharging Capacity
9 015 m’/s
FSL of Canal
El. 1348.00 m
Size of the irrigation out let
1.7m x 1.7m ROC Dud
Left Sank Command
8.215 ha
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Dun Appurtenant Works
Right Bank Primary Canal
i) Location
hi Oschar je Capacity
jiijCangi FSl
rr) Size of imflauon Otfttef Right Bant Command Area
May 2007
Rigm Bank Saddle No 2
7 52 m’/sec
6L 13430m
1 5m it 1 5 m RCC Dud
7450 na
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Bam Appurtenant Works
9 INSTRUMENTATION
9.1    General
May 2007
A  dam  is  expected  so  withstand  tremendous  forces  during  its  operational  life  it  is  therefore unpefativE  Chat  adequate  means  are  available  in  lhe  dam  for  providing  information  on  continued assurance  of  its  safety  The  extent  of  internal  dtatfwi  cannot  M  directly  measured  in  a  dam. However    diagnostic    procedures    can    provide    help    In    identifying    the    problems.    Effective instrumentation   provided   m   the   dam   serves   INS   objective   and   can   provide   meaningful information  and  efues  io  me  various  problems  and  play  ano  important  rote  in  checking  the safely  of  structures  The  condition  of  the  clam  and  rts  overall  safety  needs  lo  be  checked regularly   to   demonstrate   that   the   dam   is   performing   safely   in   accordance   with   the   design assumptions
9.2    Purpose of fiistrumerualJon
The monrtonng instruments selected for a given situation are required to function satisfactorily under very nvsh environmental condition and for long periods of time For a good design ft is desirable mat ■nstrumems Detect systems of distress and where possible to relate these Systems lo specific problems at the earliest possible stage Their prime function k. to reveal abnormalities, which may nave the potential to develop info serious incidents or failure. The instruments selected for a given situation should nave the fallowing characteristics
*    As simple in concept as is constant wflh their functions
*    Suftoeraiy accuracy ano qualify
■    Low maintenance requirements
*    Compatibility with construction techniques
*     Long term reliability and slaoilily
■    Low cost ano ruggedness
■   Simplicity ano service requirements
■    Durability under adverse environmental and operating conditions
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Dam Appurtenant Works
9.3   Types of Measurement
The most significant parameters inai are necessary m monitoring dam Behavior are.
•     Pore waler pressure and uplift
•     movements i) internal movement
li) External movement
•     Seepage and Leakage
•     Strains and stresses
•     Dynamic Loads (set&mic forces)
9.3.1  Pore water pressure
May 2007
Pore water pressure iis the most important and jsuai measurement in cmoankment flams its measuremems enables snnw the seepage pattern sei up tn the embankment and foundation after the reservoir impoundment Valuable informatwn about the behavior during construction and draw condition <s obtained
Penodscal and timely observations will pravioe the means Ol evaluating 1ne behavior o( the 03 m and enable take measures on the bass of [reserved data tmo comparison with the design In add-on various assumptions, wh ch aie commonly made m tne design, need verifications
9.3.2  Movements
An accurate measurement of interna* and external movements resulting nom the plastic OetormSbcns of upstream ana downstream slopes under different co nd tiro ns Of reservoir Operations may provide indication of the Likely development cf shear failure at weak points in the body of the embankment.
9.3.3  Seepage and leakage
Measurement of seepage through me dam body. TcunaairthS £ abutments bl the dam may indicate eroirOn or docking of OOvmstream drams and teW wells Dy increase or decrease d seepage respectively al constant reservoir Imm. Seepage ano erosion may take place aidng the lines Of poor COmplCton and through the cracks tn f-arrnalion and finis. Thts may he indicated by Such measurement. The colour, turbdlty ana Changes radically in chemical content of the SMpmg water It aiso on indication ol seepage problem and provides and provides useful mfOTrnartion aboul the performance of the structure.
------------------------------------------------------------- --------------------------------------------------------------.9! Wmr Works Design & Sapervtslort Enterprise
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Dam Appurtenant Works
9.3.4   Strains and stresses
May 20C7
The accurate measurement of stress in earth fill & rock fill dams is difficult and distribution ci stress ft compten Furthermore stress measurement and swpe of rupture planes is a matter or considerable judgment in interpretation from the data Tor use in the design analysis of earth- and rock fkll dems Slrains however may be calculated from displacement or measured d recfly
9.3.5  Dynamic load (Seismic)
Meaiuremem of seism-cdy is important as it causes sudden dynamic loading Hence instruments lor measurement and monrfonng the intensity of ground motions during the earthquake is required to oe instated Arjo- Dedessa dam project area however lies an area of moderate tn low s&UdtiCIty
9.3.6  other measurements
The  other  measurements,  which  would  aid  in  interpretation  cl  the  mam  instrumentation  data  are necessary ana are given beiow
Reservoir and Tail water «vef. Wave nerght recorders, rainfall and data about matenai properties, measurements of silt deposit at the upstTeam lace or qpm and other meteorological measurements, wlucn are essential for interpretation of the instruments observation
9.4 Plan nlng of Instrumentation* for the Dam
9.4.1 Pore water pressure
The  porous  tube  piezometer   n  a  device  lor  measunng  pore  water  pressure  primarily  tn  a foundation  But  is  aiso  used  for  measuring  pore  pressure  in  embankment,  ft  ft  more  sensitive to  foundation  pressures  or  ground  water  changes  and  can  wrfnsiand  sitting  oener  than  the conventional   observation   well.   Being   an   independent   retaliation   1   can   be   installed   el   any location even after completion of construction and its installation does not pose any restriction or hindrance m the construction of dam.
tn Arjo-Deuessa oam « « proposed to install the pore pleasure piezometer at different levels, i.e. 17 numbers at the foundation level., al EL 1305.0 m ana EL 1310 0 m and 24 numbers m the embankment section It EL132O 0 m EH3*0.0 m & at EL 1350 0 m at sections A.A, B B and C C All these are connected together th.rougn tubes and ted to the terminal well located on the downstream aide al EL 1340.80m from where these are operated upon
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Dam Appurtenant Worts
Majf 2OT7
Install anon Of piezometer th the <jam anp foundation prcvioe quantitative tnformaiiOh inducaling ihe fnagniiijde and distribution of pot* pressure and 1heir vanalLon witn time TTie pattern ot seepage zones of potential piping and effectiveness oi seepage control measures can also be inditatEtf The oata/infarmatiOn obtained from such pieromeler serve for talcing remedial measures purpose The locations and number of piezometer provided Iff (he main dam at different section are indicated in drawings NQ5 AD-F-DAMi 17-13 A 1?
9.4.2   Seepage
Measurement of seepage water al Interface of dam and its ToundatWl will provide direct
■ldicaUon m the efficiency of grout Ourtam ana mdicare about the necessary remedrai
measures The enemies analysts Of water win provide (he information Of seepage of water
through the foundation drainage arrangement and any foundation material Dfrng wished dirt Cwrecbtre measures hke grouting etc. COuid EW panned The wet spots on the downstream
s.ope Of «| abutment locations would indicate seepage problem, and remedial mMSuiH CCHJld
be suggested
Seepage  measurements  are  made  by  providing  notches  and  weirs  ai  pdinis  wnere  seepage  s taking place and seepage discharge pan be computed
Y-notcnes  are  installed  in  the  surface  drain  a*  the  t«  of  dam  |q  measure  seepage  discharge  at regular interval of time
9.4.3  Surface movement measurement
Thr mMSurOfttem Of surface movement of the embankment dam shall be made by means qf installing 22 number of surface settlement points On the dam 5*0 pe, aam Orest at 50.0 m center M center *nd Shall bt monitored by using a thewoMe at regular inHrvan from bench mart s stad sned and readings each Imt taken shall be compared with (he «tdie< reading to anwe at the sefllcrtteht Of the Surface. The arrangement showing IM prevision of surface settlement movement points in indicated m drawing AOF-DAMS1G
9.4.4  Parapet Settlement Point
10  Mos  Parapet  settlement  pant  have  been  msteHcd  in  the  parapet  wall  @  50  0  m  Ofc.  The Parapet  seflltmeryi  pome  compressing  Of  15.0  mm  diameter  mild  Udei  rod  0.34  m  long  welded 10 a S10* piflte of 300 X 300 X 0 mm The top 45Q mm of mawnry wall In a length b! 600 mm has Peen made In M^KXJ concrete. The tettfemem pomls embedded in concrete with MS
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Dam App urteninE Warks
Sfiy zoo?
projecting  40  0  mm  above  parapet  wall  wrth  each  roa  crossed  marked  far  measuring  horizontal defied ton
9.4.5  Horizontal and Vertical Movement Measurement*
The installation of instruments lor measuring movements are provided at critical ioca1»ons maximum vertical movement normally occurs at rn»d neighi of structure and maximum horizontal movement at middle of slopes Therefore 5 Ho* horizontal movements instruments are proposed at rmd slope of structure thaT is al EL 132S.0. EL 1340.0 tn in different sections and 6 number of vertical moment instrument at EL 1350.0 m and EL 13W m For recording vertical movement cross arms installation has oeen proposed Similarly inclinometer instruments nave been proposed for registering honzontaf movements
9.4.5  Earthquake Measurement
Arjo-Oedessa dam site is located m a seismic zone of medium to low intensify and mere is no earthquake recording station m the vicinity of the projeci area. Records to snow the earthquake
events experienced in the project area are not there:
The msirumems for recording of seismic events proposed to oe Installed for the cam consists of one attdeograpn ar the base of the dam ana one at the top of the dam. Strong motion accelerographs and structural response recorder are to installed at the base and at the top of a am The location selected Should be free from the background seismic noise erected due to vibrations of the appurtenant works The instrument located at the top would provide information about responses of structure resulting from earthquake
9.4.7  Other Measurement
wave  rtwgffl  Recorders-  Wave  height  Recorder*  insra  ll&d  wouln  be  helpful  in  finding  the  wave height anq in deciding the free board requirements on a more realistic way
Rainfail   measurement   of   rainfall   will   be   heiptijl   for   interpretation   of   pore   measurement   and seepage development in earth d»m
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Dim Ap punenant Works
10 SPILLWAYS FACILITIES
10.1  General
Mi y 2007
Spillways are pr&vflfd separately at th conjunction Wfth aamS t& P?ss fkjaOwaler far reseWCir Tafluflation and ter salary at dam HruCture The venous types °T SpHways generally tail into «ie Of the following types w are made & a combmancn of this
i) Overflow ogee ipritway «) Gated type                                W> Shaft" 9101? hCHd
Vi) Skm CTannflHpcllw»y          l¥) Syphon spillway              V} Chute spillway
For Aj}i5-CJmws3 cam wruch ts an earth and rocx fiH Mrt 1ne spillway wrfll". pf 125 Om With flood lift of 2 62 m has teen provided The spillway naa sufficient CipaCfly to pass the d&tgn fl&Od as that when the flood discharge impinges at foe time when the reservoir is at FRL, the flow Ml would npi result in ouertoppng Of the Pam. Besides providing sufficient capacity the spdway ts hy*aulicalty and structurally adequate to diSSipare the energy associated with the discharges
tt  h«  been  waled  such  that  spillway  discharges  will  not  erode  W  uhdtmnine  the  downstream toe of the dam The frequency of spillway use depends upon the Sum Ql characrerizaltnn of the drainage  area  Spllway  flews  mH  result  during  floods  0<  periods  of  sustained  high  run  off  when tne caps cities of other facilities are exceeded
10.2    Location
The spillway has been located on the nght flank in the natural saddle NO.1 upstream of ArjCr- Dedessa dam un. The location considered for apdlway a sucn that rt does not interfere wtth the fonctwniog and performance of other structure of the project The topography geological set UP ana layout of other structures were lhe main consideration in deciding the location of the spillway in Che natural saodfo ho.l OP the nght flank of lhe dam. The discharge earner iq provided in the excavated rock ano wffo a enute ending in an energy dissipation arrangement The Other alternative arte tor location of spillway exammfrd was Ift a saddle on lhe left flank of the dam. This was nol considered suitable as rt involved large excavations due to rls higher Bleviteri Coftudffing the rock type inc geotechnical investigation report, Stilting basin type of energy dissipation arrangements have ww considered
10.3   Spllh**y Layout
The maximum Spillway discharge tWS been computed by flood routing Studies by the hydrology group. The tpflhrty width and the flood lifts have been worked Pul for venous combinations of
__________________________________________________________________________________ 95 Viter W'otks Design i Supervision Enterprise
In Asmdillfln >LLH tnrsrtoiUciraiil fcosuLLaou sod Teeboacrtii FTL LtiVjoDedeu* irrteados FTcJefl
Dam Appurtenant Work*
discnarges taking into consideration the Topography an<J the foundation condition of the site wti-cn have influenced the location type ano other components of spallway The spillway wrdtn Of 125.0 m width ano flood kfl of 2.62m tor Io the routed spillway outflow discharge of 1165 0 m’/sac for a peak inflow of 1050 m3rtec for a return period of 1 in iMOO nave been considered The different combination of spillway widtn and flood lift considered are given in Tables 10
T*pi» 10.1. RSUWO
flpoa BawO on LLd Dutritiii lion Fem out flow 1950 m f"<C
s.
ho
Spillway
widln in
Rokftcd out flow Q out
Flood
Max surface
Area |Km )
r
Surcharge
storage
(Mm )
r
1
50
aoo
3 75
99 11
1693 0
2
75
951
3.21
87 49
1637.1
3
100
1069
2.87
96.45
1602.0
4
125
1165
2.62
95 71
1577 0
5
150
12+6
2.42
95 12
1557 7
6
175
_____________
131*
2.27
9+65
1542.0
The saddle hlr>-1 upstream of the aam axis on the right flank have provided the location at advantage for the spillway m meeting Hie requirement of being independent in the operation and pcflormance of other components ot the project The spillway at this location is not rrterfering with the location and performance of irrigation outlet from where rvgtrt bank primary canal i* taking ofl in the near by saddle Mo-2.
The downstream docnarge channel from the spillway n» been abgneo along the natural drainage and wilL outfall into over Wama The natural drainage after a distance of about 1 O km trom the stilling pasm has Peen channetiZM The general layout plan and section etc. of sprtvrty is shown in Drawing Nc AD-F-DAM/20.2H 22
10.4 Design inflow Flood Discharge
Sptlway has been designed to have discharging capacity sufficient enough to pass the inflow flood* correspond'ng W probable maximum flood1 (PMF), as from both the Might and storage capacity aspects the proposed ct*m I* classified as a Large dam Indian Stargards specify (hat rf the failure of aam poses danger to human kfer the apiftway must have suffi«n| capacity to accommodate ttie touted flood discharge corresponding to probable maximum Flood (PMF) a«j if the failure of dam would result only in heavy damage to property but does not pose
______________________________ _______________________________ ________________________ .96 Water Works Design & Supervision Enterprise
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appreciable <rtk to life then 1he spiMway may be designer! For fl&OO discharge corresponding Eo 1 in 10.000 year reEurn periM The cam tocauon n m an area where failure may pfQOsoh remain restnotad to Ehe imgatmh farms a no I he dam area rt self LOSS to human life wflum pnobawy be minimal. For Such ■ situation and Ftrf the sake OF economy a r&uEM flood discharge corresponding to 1 lb tO.DOO year return peripa or half Ol prownte maximum flood (PMF) which war IS greater has OCtn considered as mere I5 nor mucn tlltxtelten down stream of (he cam sue ana the sam ■$ located m a remote area. The Prohaole Maximum Flood (PMf; M wmputM and provided Oy the nyorotogTr group is 3690 m’xsec and the T bl 10 QDO year return pence flow value works tut fa 1&5D m3rs bawd on LLG distribution Halt PMF value works uji th 1?ft0 0 mVsec since half PMF rs »S4 than that, 1 in 10 DOO year retum penod flood, peak inflow q( 1 m 10.000 year return ptWIOO nas peen ccnsmered FlOOO routing studies tarried oul with different combination Of spillway Widths. FlnotJ lifts Of 2.62 m and spillway width of 125 Q m is considered foi hydraulic resign of spillway structure
1D.5 Gated ¥/■ Un gated Spillway
A gated spdlway normally provides the most economical means of passing the deSign flow
discharge whereas an ungaren spilfway ts inherently safer and rt the SimpMSI form pt spillway
which automatically releases water wherever the reservoir water surface rises above the crest.
The ungated spiFhvay has the advantage nt having I ran me free operation as there are no opcralmg mtcMUrtmt oV malfunctioning of control gales The mam advantage has in (he elimination oE Ehe requirement for constant regulation ano attendance Of I he control device by an operator and the freedom from maintenance ana repair But on the other hand R has (O be tocateo at full reservoir lever TM makes the flood lift in passing lhe finoo discharge Over the spillway crest high. The maximum water levels would generally become much higher then the naxrm-jm wattf tevd (MWL) in case of lhe galed Spillway for Ehe same FRL Tins results m «m crest Io be kept high stave the full reservoir hvbi
For  Af}0 -  Deoesu Dam me ungatad  spillway  4  considered  suitsple  ItK the trtuation  due lo the remoteness of the strudure The OMign flood 4 not targe and Che flood lift (s not very high
The design and features o! spillway structure have been worked out accordingly conforming to Indian Kanoaris The Spillway crest lew Of 1356.0 m nas been considered Thrt vWth
minimum free bond above maximum water level cl 135H.60 ana normal free board required at
FRL 1356 0 have been worked uuL in both situations the lop of dam works to be at 1560 SO m
The spillway capacity tor the tnesen apltlway «ndth and Hood lift is adequate enough and dam
is not over toppea
________________________ _ _________________________________ __________________ *7 Water Worts Deiip) 1 Supervision Enterprise
la Urtcteasa with toiertfl n UnemaJ CtrmuJttalf and TBcfanaoms Pvt Ltd.Ar]Q'DeteE34 frrlgittan PtoJecI
Dim Appnnonant Works
May 2M7
The features. of the spiltway. chute and endrjy dissipation arrangements shall be lasted on hydraulic mrxH studies far their efficacy ano performance m regards 1o Chau geometry CMlrrbulion of flow over the ogee spillway, for a i Menis if any pressure distribution on inclined chute and performance Ol Wu1e. docks. fdeMaited silk. The layout of I he spillway Showing approach channel control structure, chute and stilting basm and IhS tail race cfiannfri are Shown rS Drawing Nd AD-F-DAM^I & 22
1D.$ Energy [Jisgipatton Arrangement
The energy d^ip^n below hydraulic structure IS. ra*y Vrfal in the design and construction of dams weirs and cartages The energy dissipators arc prpvioed Io reduce high velocity flow Id i vekrcrty lew enough 10 rmninuie erosion of the natural rwer bed The reduction in vfllOCrty shall be accomplished by i» Hydraulic Jump rype stilling bSSJH Of (b) Buckei rype dlwpalora
These  arrangements  are  mosl  tommcruy  used  for  dissipation  of  energy  depending  upon  the roc* and the geo-tachnitat conditions of the Downstream tad water
The type of energy dissipation arrangement considered based on the topographical and geo- lechhoi investigations has been proposed Id be the Stilting basin type The designs at the energy dissipation arrangements nave P«n earned oui as per Indian slanaards code The n ypraul it pesign of stilling basin type of energy dissipation Hrrangarnenl has been done. The bengtti of slitting ba s n rs computed and works but 10 25 C m The Otpih of water in I he stilling basin ft wmpUIBd and ts equal i» 6 0 m The &1her parameters mo feature like chute WOOK end sill and dentaled stil have etso been worked out and provided accordingly
10.7  Approach Chin net
Approach channel is reguiteO 10 draw waler from the reservoir for conveying It 10 Vie control structure. The I*you of the approach channel n selected tn such ■ way that the mcreasw vAWOty Should be limited and the cnanne. curvature And tradition ere grsdu.il so (hat the head
■MS through lhe channel is miiirrtal and uniformfly of flow aver lhe crest <jf spillway ft obtained. Head   lots   In   the   approach   Channel   has   an   effect   th   reducing   the   spillway   discharge Furthermore   high   vetocity   may   stjo   necessitate   lining   cf   tire   channel   depending   upon   (he foundation  condition.  Uniform  and  aven  distribution  of  flow  h»  therefore  been  ansreed  over spillway  crest.  The  arrangement  of  layout  provides  for  guide  wails  kepi  at  nghl  angles  (0  lhe axis of the sprllway structure In 150 m length on the upslream of lb& spiltway axis and therefore <re pravdml with Cuhraiure of radius 15-00 m. The lotal length of approach channel has been
--------------------------------------------------------------------------- ----------- 9»
Wttur Works tailgn 4 Soperrtiilau Enterprise
tn Usoclrtlon eftr. IMtttt nUnrntU Co am I tin u and TmUmowu f*n Ltd.ArjcDsdiJn IrrUiXIoii Project
Dam Appurtenant Wcrits
MayZW
Kept 15 OC m and a toe wall has been provided at the end of approach slab Slone protection of 10 Q m length over the whole width of the approach channel nas teen provided
The depth below crest of approacn cnannel and approach velocity nave an important influence on the dischang* Ovt* over £**41 A greater approacn depth with the reduction in approach velocity results in large coefficient of discharge value cd' friuS. for the given head over the crest a deeper approach w.ll permit shorter crest length for a given discharge in the case of Arp-Dedes-sa Oam spilfway location is in a saddle and considering the topography and the natural ground level me bed of the approach channel has been Kept at EL 1349 0 m for a Slr»gft1 length of 15 0 m length and the crest of the spfBway is kept at El 1356.0m
10.8 Spillway Structure
The overflow spillway SWCture adopted for Arp Dedessa Dam >s • control weir wn.cn o1 an Ogee ship in profile It is located m saddle Nc:1 on the right flank of the dam and 500 0 m upstream erf dam Snt The geographic location of the spillway structure are defined by coordinates at ns cemrai point
The Ogee profile to be acceptable should provide maximum possible hydraulic efficiency,
structor* SHbdrty and economy and a<so to avoid formation of sub atmospheric pressures at
the surface
The overflow spillway structure has been provided a length of 125.0 m wth 5 bays of 25 0 m do each separated by 2 0 m thick t>er 4 m numoer The piers support the 4tee> truss structure walkway of t 50 m width The crest level of Ogee weir tS kept at EL: 1356 0 m The foundation of the spillway structure has been kepi on excavated firm roc* ano is founded at El 133B.0 as revealed by drilling borehole at SP-1 location which is at the bender qf spillway structure.
10.9  Ogee Weir Profile
The upper curve of (he ogee generaly is made Io conform closely to the profile of the lower nappe of the ventilated sheet falling from a sharp crested weir Flow over the crest is made to adhere to the face of toe profile by preventing access of air to toe urwersiOe of the sheet For discharges ai designeo head, (he flow glides over the crest with no interference from the boundary surface and attains near maximum discharge efficiency The profile betaw the upper curve of the Ogee is COhbflued tangent along * atop to support the sheet on the face of the over flew A reverse curve at the bottom trf the stope toms the flow on to the chute, men to toe sliding basin end thereafter to the spillway discharge channel
- ------------------------------------------------------------------------------------------------------------------------------------« Water Waits Design L SupertUI an Enterprise
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Dam Appmnenant Works
Maj 2007
The jngated spillway crest is kept at FRt EL 1356 0 m The overflow section adopted is Ogee snapea weir to be omit in reinforced concrete 125 0 m w>de with vertical upstream ta-ce The width or lhe tprilway nas been athveo si by various combinatinn ol flood lifts ano widin and urong the oasic weir equation for passing the design flood Abutment ai each cr*d ct the crest has been taken to neigh! above 1Me water profile and providing tree board The Ogee profile has been Designed for upstream and downstream crest profile as per the IS 6934 1373
The  upstream  crest  profile  is  kept  tangent  to  the  vertical  face  and  should  nave  zero  slopes  at lhe crest axis to ensure that there is no discontinuity aiong lhe surface of flow
Upstream profile
The upstream profile aoopled conforms to lhe mjuauon
y . OJW + MTWW)' *
1
_ 0 43,
4. O.27dff)o<"
Hd"*i
Where. X,Y = CartaSian coordinates
* Design need
The               of * tor vanous values of X are ooiamea Inom the Tabtes in Fig 3 pf the Indian
standard code
Downstream profile
The down stream profile snail conform to lhe equation
i d                        au
X ■ 2.0 fid. Y
rtbere, WJ = oesign head
and , X & Y are coordinate
The profile has been designed for one value of the design head (Hd) only and h»j been be chosen to give the maximum practicable hydraulic efficiency m neeping with the operational requirement, statdrty ana economy rtmrevar, generally the spiUways are operated under concMions other than the design head and at times sub atmospheric pressures daveio-peu lead 10 cavitations. The lower the design head of the crest profile lhe greater will be the discharge coefficient lor the full range of heads For design head exceeding by 25% np harmful captations K seen io develop. Design head is usually kept at 75% - flO% of maximum head Economy in the oesign of an Ogee crest may sometimes be affected by using a design head which is less than the maximum expected head Use of smaller design head results in
-----------------------------------------------------------------------------------------------------------------------------------<00 Viter Worts Design & SupnrrtslQn Enterprise
In ItuKiilkiB wtU) iDWtODUMsttl Couullants uid TKtaeenU Pvt Ltd.Arj^Dedeua Irrlfattoo Project
Dim Appurtenant Works
May 2007
mcreasetj  di  scnarg&s  from  me  fulh  range  of  headt  The  increase  in  capacity  makM  11  possible to Bcfueve economy by reducing til her lhe crest length or the maximum discharge htao
10.10   Spillway Chute
The spillway cnute of 125 0 m width eo pass the design flood discharge has txon provided oolcw 1he spillway giO&S It will envisage excavation tn roc* to math the designed Itirti The Wk is repcneu co m avaiaoie at El 133S.0 m as revealed in me geological 8 geo-technical report The twigmal ground level al Ute saddle anee is around 1350.0 Thfi material ccnsislmg of ovevtiupoen sno IraourwTweathered and iocsc IOC* rS to be removed to lay the foundalrtn for spillway sludies, chule end stilling oasiri on tte firm iekL The Stilling P3S«n foundation has been lak) on firm rock and tnickteis of i5W mm of conertwe floor prpvioed The same n exienoed up si ream to form tpundMipn for the spillway ana Chute the concreie floor is anchored Id Che rock foundation oelow by 25 mm p grout anCTWrs at 1 5 m tfc and 3-0 m deep Over the Concrete floor cyclopean concrete with 60 % stone *40% concrete df C-30 grade ts placed and well compacted conforming Io the shape of spillway. 1500 mm thfcltnm ol reinforced cement concrete (M-50j grace is paced over the Ogee spillway and chute all around with 25 mm p 1 5 m efe ano 3 0 m deep grout anchors as sncwn n the drawings ol spillway structure Under drainage arrgngemenl has been provided 1o prevent 1he foundation mgienal from being cached into the pipe below For reducing the uplift pressure, Grout curtain 25mm £■ of 3.0 m depth Q 1 5 m cte nave wen prpvqeo In the entire spillway xmglh upslream ol lhe Ogee Werr to prevent any seepage from lhe reservoir side taking place pod te prevent Building up Of uplift pressure under the spillway chute and Stillmg basin foundafion. The general teyoui of lhe spillway facilities is Vrdwn m Gnawing No AD-F-DAM/20
10.11  Structural Requirements
The retaining wans for sides of entrance cnann&, d scharge channel and smiling basin have been assignee Io with stand all poss-tHe combinaMn ol venous loading hke back fill earth, of W* pressure water pressure. live low roo^iarije, upfrft pressure ano forces due to horizontal ana vertical s&smic acceleration. The structural steel Mails hM not been indicates Irt the drawings and is W be provKSea at desa-.lea Assign scage
10.12  Floor lining
Duong  ftte  spillway  flows  the  floor  fining  «j  subjected  1o  hydrostatic  fprc«,  boundary  drag IWC«. uplift and dynamic forces dua Io flow impmgemenl When there is no spiirthe lining H
-------------- ----------------------------------------------------------------------------------------------101 Wittr Works Design & Supenrtolon Emerprtse
In IsHdxaouwtQL iKHnnOMiitU Cc rjnJtiirj ini Ttt.tiiLotT.su rvt LLLMotwiMsa Irrlgtitoa Project
Dam Appmtenani Works
May 2007
subjected tp the action oi expansion and contraction due io temperature variations weathering ana Chemical deterioration, effects of settlement ano buckling or 10 uplift pressure due lo under seepage 0* high grouno water condition II is recognized in the IS coae that fl it not possible to evaluate these uanous forces that mignl occur and aiso not to make the lining heavy the thickness ot lining ts made on more or less empirical basis and reliance is made on providing
■jnder drams, ancnors. cut arts etc. to stabilize lining.
The IS oqob provides intcuness of Immg m me approach channel of 15 cm 10 3G cm mice concrete unaer normal conditions (n the inclined chute the concrete lining thickness as been sepf as 1 5 m In the stilling basin the floor lining thickness a Kept 1 50 m
in the inclined chute, the cN* profile of Ogee wwr, very high velocities of flow iane place causing abrasion aue to suspended wit load Once pitting starts, repairs become cMficuil It is proposed that well oesigned m» of high perrormance concrete jsmg silica fumes «S used. Like wise, m stilling basin also, where nydraulic lump forms Sucn concrete shOukJ be used
10,13 Water stops and joints
Water stops ano joints are provided as per (he IS cooe which specifies that lining should be laid m panels so as to mane the entrance cnannei lining a reasonably water ng nt upstream tb reduce upifl pressure on the control structure see pints in the lining have been provided with water stop? The water slops ar* also to be prodded in longitudinal joints. transverse joints and in the joints of Side walls where seepage behmd the walls <S undesirable
Water stops nave been provided in the joints ot stilling basin floor lining so as to avoid
circulating flow under the lining due to differential head on the joint m the zone of hydraulic
jump
The transverse joints have been provided with 13 mm off set as shown in the drawing so as to avoid high velocity ftcw striking agamsl the edge of the lower floor cause water to seepage ttWOvgn the joints under a very heavy pressure and design or uplift the lining A cut oft has
been provided to prevent lifbng of upstream edge of lower slab due to differential sefflemenfl
10,14     Drainage System
The stability Of floor Inmg h increased by providing under drams as these reduce the uplift pressure on lining. The drains under the bmng consist of a network cf pipe drams, which (otow the jCtMs in the thing The drams provides are non^pertorated cement sewer pipes laid with open joints In gravel and embedded on a mortars of concrete pad lo prevent the foundation
___________ ________________________________________________ 102
Water Works Design t Snperrtslon Enterprise
la Usaaadfln elth. tats wo nite tauJ Cn nsulLaau lad TechexrtU Fit, Ltd.VjoDtiEMi irriEitun Project
Dam AppiarteniciL Worts
May 2007
material from being Jeacned into the pipe The drains under ihe incJintd chuie have Wislr cullet open m discnarge channel itself through ihe sidewalls The outlets are connecied i& Ihe p^e
□rain  The  drams  under  the  lining  below  maximum  tail  water  level  ana  smi  ng  uasm  have  their KTltMs into the Chuie blocks of 1hE basin. The drainage arrangemenl of selling Casih have peen Kept  separaieo  from  that  pl  the  olhar  floor  lining  Pipe  drams  nave  also  bwr  provided  al  the foe  of  the  heel  of  me  sideways  io  coifea  seepage  water  from  ihe  btdrfIK  and  relieve  the  wal from  water  pressure  These  pipes  have  th«T  OtftlEES  prbmdeo  in  the  discharge  channel  thro^tfl sidewalls
Anchors cars have been provided under irw foundation of chule spallway and HlilJing oasm IO Increase 1ne effective weighd of the slab against displacement due IO uplift ann other forces The grout ancnor pf 25mm f @ 1 5m f g/C (Staggard} 3<l m long The diameter of the hole into
wncri anchor bars have Peen pJaced and grouted Should not be ieSs than 1/2 frme tfie
maximum transverse dimension ul the Mr The spacing, dramater of Dol*S depin of the anchor
Mtt and type of anchor To be provXJtd are |p be decided by the actual pull out tests
11).15 Hydraulic Model Studtes of spillway structure
Hyd'BulK model studies of lhe spillway structure are required to be earned pul Io assess trie pedonmance ano effroency d the structure lor ranous intensity of discharges in lhe spillway
The mtwei studies canted out are helpful in carrying out modifications in the layout add
geometry of the camporienls Of the Structure. The performance and efficiency is IO be sludrtd
m relation to.
i}  The flew  partem m the approach channel  anq geometry of gnd waifs.
nJ Flow distribution over the Ogee weir
Hi} Distribution of pressure over inclined chute 8hd neod for aeralion vems
to be provided if requited
nr) Ensryy dissipation arrangemern performance regarding hyflraubc jump
formatian and modification in designs rf any culled for
The hydra Jic ItiMtl Studies in respect of above aspects heed to be earned oui a! the time ul canying CUI detailed designs ang before la+i-ng up the flduSi construction of (he abdvt Spillway facilities
103
Water WorUs Design & Suparrblotz Etitfrprtsa
la UMdaOasTim IflUranrOn ratal PathUlIXoU and Tse hnoertts Pvt Lw_Irrif iDon Project
Dam Appurtenant Works
10.16 Zoning of Material for the spillway facilities
MljW
The grades  of ctwcrwe prapnod to be In different i&cairans  of tne spillway  facilities  nave
been md>tated below
Sr
No
Location
Compressive stnagni of
concrete (N/mm2) 28 day
strength
Maximum size of
Aggregate inim)
1
Spillway Ogct cresi spillway glacis, chute, end sill 6 Ch-Ute raefcj etfenor 2 0m IhicknesS
25
40
2
Stifling basin exterior 1.5 m IhwJcnras
fid
(Using silica fumes.
20
3
Spillway ptera. RCC relain ng watts stilling basin except 1.5 rn manor ihvAness
20
40
4
The   lovndation   lor   filling   up CIWlCH
15
20
5
Gravrty    MCtiW    l&r    retaining wsls
20
40
6
Approach channe i fifoor
IS
20
l(M
Water Works Dsdgn & Saparristan Enterprise
til LiuanUnn wlUi teuroanUBnul DOMUJtlnls ud Tschoacnta PtL. t**iHydraulic Design Computation
for
Spillway facilities
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105Mo-D®(essi IrrlgiaQii Project
Dam Appurtenant Works
11 HYDRAULIC DESIGN
11 d Hydraulic Design of Spilfway Facility
May 2007
rhe spillway i& da-signed co pass a discharge of 1 in 10.000 year return pe/iM or M PMF whren ever 4 greater The discharge of (he 1 in 1Q.DD0 year return period is computes as 11(55 0 misec and gives a ritgtier value Therefore this value of discharge has wen considered in (he hydraulic design gf spillway
The  routed   out  flow  discharge  as  computed  =  1165  (rn^gec)  For  a  spillway  wroth  of  125  0  m ano the Surcharge heigh! for 1hi& Computed = 2.62 m
Where, Q - cd L H”
L= 125 00 m
Le = effective width Df spillway ana is detained by considering abutment and pter
contraction erleci.
Q - H65 m^sec
The  surcharge  neight  for  routed  out  flow  discharge  of  1165  m^/sec  ano  width  of
125.0 m = 2.62 m
le ■ L - 2 Ha (NKp t Kaj - width of pier
= 125 - 2 « 2.62 (4xO<Jl+ Q.1) - 2x4
■ 125-5 24x0.14 * 6.0 m
- 116.27 m
Hence Q = cd x 116.35 k He"
He- (1165/22x116.27)“ =2.74 m
Velocity * O/A = 1165/S 74 x 116 27
■ 1.146m
Le= 125-2x2.74(4x0 Gl-0l)-2x4
= 125-6.46 (D.14J-B
-1254>T7’B
-116.23 m
Va Ftewsea - 1165/8 74 x 118.23 - 1 147 mfsec
106
Water Works Design it Supervision Enterprise
tn moeuUon WMD ImanactUoflEtiJ Canxultutt lad Techs g m u Prt Ltfl.Arjo Dedessa Irrigation Prejan
Darn Appartenant Works
Miy2OT7
l  J.J47*
‘ 2 X9SI
= 0.067
H„ - He - Ha
*2 74-0.067
■ 2 673 ni
For   aesign   erf   Ogee   snaps   □   lower   design   head   is   used   as   rt   increases   the   discharge coefficient for nrgner flows than me design flow
Adopting 98.0 % of heap
Crest of Ogee ■ 1356 0 m
Depth of water over Ogee ria = 2.673 x O.SB
-2.62 m
The   computabon   for   the   Ogee   spillway   profile   for   both   upstream   ana   downstream   nave   oeen done and are contained m Ta&ie 111
For  Arjp-Dedessa  Oam  spillway  the  gooo  rock  is  availaote  at  1336  0m  as  per  the  spillway  drill note data at spillway location SP-i
Therefore floor of stifling basin 13 proposed TO be kept at EL 1336 0 m The chute Is proposed with slope of 2H:1V
Velocity at crest of Ogee weir
V = Qi'A = 1165>'116.23x2.54 = 3 95nVsec
Calculation for dj
By using Bernoulli's theorem and neglecting all losses
TELUfS -TEL + n
Ll/STEL - AZ+ di + ha
Water Works Design & Supervision Enterprise
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Dim Appurtenant Works
= (1358-1339}+ 2 54+ 0 795
s 18 * 3 335
= 21335
D/S TEL = dj + ha?
na2 = Vj /2g
VayZflO?
z
Vj = Q.'A = 11B5/125jtdr
V,= 9.32/d?
a ha =
9.32J
d }x 2x9.Si
= 4 42/C/
SutMlrtLrtnfl values in (he equation aoove Qs tel »ch + n#j
21.335 =d  + 4.424/j/
1
21.335 d:3 •< +4.42
ar< + 21.335            +4.42 = 0 Saving the equation for d ,
t
dj ■ 0.46 m
^=116^125x0.46
= 20.28 m.'sec
20.26
= 9 54
Water Works Design 4 Supervision Enterprise
li iuactxDpn wtlk totm until nta] Cctualluu ud Totfanctnu m LliL
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Dun Appurtenant Works
Using horizontal type of Hydraulic jump
dj= 0 5              +a/2 - >1
= 0.5 X 0.4b [/l +8*(954)1 -1]
• 0.5 j 0 46x26.00
= 5.98 m
M»y3M7
Since  Frouoe  nurmber  is  more  than  4.5  Basm  Type  II  shall  be  used  From  the  graph  DeTween Frauen s number and length of Basin for Ffoudte number 9 54
Length of Basin =43x596 = 25,7 say 26.0 m
Mmimun   Tail   water   depth   required   from   graph   between   Froude   Number   and   Tail   water   depth (Design of small oam oy USBR/
7j<7 wn/enfepfh
0.46
Min Tail water depth >13 4 x 0 46 To be acmeveo
= 6.18 m
say 6.2 m
Basm Appurtenances (From the IS standard)
• Chuis block. height. Width and spacing
D. = C 46m say. 0 50 m
Spacing from side wall — ■ —- - 0 J5 m
*22
■ 0.25 m
Chute Blocks snail be provided at junction of horizontal floor and slope of chute
Basin  Blocks  snail  Pe  provided  at  a  distance  of  0  B  DT   farm  the  juncbcn  of  horizontal  flow  and slope ot chute ■ 0 B x 5 98
= 4 7B m. say 5.0 m
------------------------------------------------------------------------------------------------------------- IG9 Waler Warks Design & Superrislan Enterprise
li AMO tilth) n with InlarrnnUMnul CoasaltMts ud TBchnotrau m Ltd.Irrigation Project
Dint Appnrtenint Works
* Basin Block
Height of Basin Block snail be taken from Graph of Froude Number versus — i$ Lode 4997- 1960
For Frourfe Number 9.54
^--235
A
At-235x0.50
= 1 17 say 1.20 ma*
Provide ho = 1.20 m
Top width = 0.02 ho
= 0.02 x 1 2 m
■ 0.24 m
Provide 0 25 rr
Stope DfS snail be 1.1 ancf <J/S shall be vertical
Spacing and length Of crocks W ■ 0 75 ho
= 0 75 x 1 20
-090
Provide t Ofn
Spacng from sidewall ■ 0 375 f>.
= 0.375 x 1.20
= 0 45
Provide 0 5m
* End Detail Sill Heigni (h»)= D.2 D,
= 0.2 X 5 98
* 1.196m
Provide 1 25 m
Top width ■ 002 D,
-0.02x59®
Witer Work! Design & Supervision Enterprise
tn kMocladen with InwcntUmical Can»ltuu and Tecii noeri u Pvt Lu.
ItoAiJo-DedesH Irmtaaon Projeci
Dam Appurtenant Works
= 0 119 m
Provide 0 125 m
Spacing and length at bottom = 0 15 D;
-0 15x5 98
-0 79 m
Provide 0 90 m
CMS Slope 3 l u/S Slope vertical
May 2007
End  sill  shall  start  nght  from  side  wall  ano  no  gap  from  side  wail  shah  be  provided  The Appurtenances far stilling Basrn II are snpwn in Feg 111
* Tall Channel Design
It is assumed that in the tail channel the velocity shall be Kepi at 1.5 iwsec The width of the channel is Kept the same as kept for the spillway chute
The width provided shall Be 125 0 m Assume depth of water of 5.0 m in tail channel The discharge in tne ted channel is given by
Q=AtV
11-65
1.5
W776 7 sq m
That  is  area  of  cross  section  of  the  tad  cnarmei  required  is  776.7  sq  m  and  area  provided  in the tail channel rs.
Area of 6.0 m depth Of channel with side slopes i: 1
A = (b + nd} d
= (125 + 15x6) 6.0
» 784 0 m/ sec
The area provided is more than required area
The bed Stope a cattuiared by using Manning s Icvmua as given beipw
where
n
n - is the rugosity coefficient ana taken as 0 025 for rough surface
IH
Water Works Design & Supervision Enterprise
b tMocteUnn wttb lutercotulnEiiti) Cflosultects ud Tcctmarrats Fn. Lld.Miotefassi irrijidoD Project
Pun Appurtemm Works
HVBMT
Wetted Penmew a computed as fl -
j? - * -
784 q
‘ P " 125 - 2 j 1.41x6.0
784.0
125 + 1&W
= 6.52 m
R1 ’ = (5.52/ 1
= 3 123
1.5 x 0.025
3 123
= 0 012
Say 1 in 7000
Al the end or 500 m length after the twin, beo drop will be
=          = 0.070 n
7000
Bea Elevation ■ i33fi - 0 07 m
= 1337 93 m
■ Free Boa rd In the Channel
Free board in the channel conauoed flaw at supercntcai stage, surface roughness, wave action nr bulking and spray are retalM to the velocity ana energy content ana is given by the emptficai relation as uetow.
____________________________________________________ _________________ 112 Water Works Design & Supervision Euterpris e
to *3Md»oon with lntertindBflQt*] Consultants and Tnehoocrus ptl LuLMo Dtdas si Intgiliac Fnijnei
£amAppurtenant Works
Free Board (infeet) = 20 + DO25 v tfd
= 20*0 0?5 x 1 5 X V«.D
= 2 0 * 0 025 x 1 5 x 1 fll
= 2 06 It or
■08m
say 1 0 m
Top or Bank elevation or channel
= Water elevation + Free ooaro
- 1344 0* 1 0
= 1345 0 m
■ Elevation at dlttarent places
Bea frevation of Tail waier channel = 1344.00 - 5 9B
■ i33BO2m
say 1338.0 m
Water elevaton in the tnannel -1J3B0 + TWL
= 13380*60
* 1344 00
Water itvflr in Tail waler cnanrwi ai 500 m Djs
D/S = 1344.0 -0.07
= 1344 0-007
= 1443 93
Bed level at 500 m OS in tail water crwnneL = 1343 93-6 0
= 1337 93 m
« Fr>« Board in still I ng Basin; (from USBRj:
Free bean) in staling basin is provider] so that stilling basin walls are not overtopped Py the surges splashes ano sprays and wave action set up by the turbulence ol the jump The surface roughness Cl flow is related to the energy dissipated in the jump and tn the depth of flow m the basin.
_ 
______________________________________________________________________113
Water Works Design & Supervision Enterprise
H AssQCUhan wtli tarmondneolxl ConsultxDls tad Technocrats Kt LUMo-Deduss [rTljitlon Project
Dim Appurtenant Worts
Free board <s calculated ny the following empirtcal express^ which hl* performed satisfactory
Freeboard {in fl) = 01 (v, * dj (front USER)
- 0.1 {20 26 * 6> x 3 2S
=B6n
26 m
Top eevadon of stilling basin walls
■ Water elevation in basin ♦ free tx>ara
= 1344 00* 2 50m
= 1346 60 m
» Layout p»an of spillway is shailin Fig 11.2
11.2   Irrigation Outlets
Miy 2O(F
Two Itngabon outlets, one near the left abutment for the Lett Bank Primary Canal ano the other on tne ng nt flarw. saddle - 2 along with the intake structure for the Right Bank Primary tana - are provided for withdrawal of water supplies front the reservoir in a regulated manner tor meeting the irrigation demana in the respective command areas The control gate structure for each is provided on the upstream for regiaabng 1he releases as per toe requirement of irrigation canal The gates are operated by a hydraulic hoist. As emergency gale upstream of the control gate has been provided for emergency operation if requireo
11.3 irrigation Outlet for Right Bank Primary Canal
The irrigation outlet fo< the Rignt Bank Primary Canai has been located in the right flank saddle No-2. The original ground level ait tfos location is at EL 1358.0 m The drill hole ADS-2 has indicated the over buraen of about 20.0 m at this section The Irrigation outlet has been designed as a cut and cover conduit and placed on hard excavatec root stratum to carry dudiaige to meet the imgabon demands for command of 7450 hectare as per the data provided by the imgaton gro^ The invert level of the outlet has been kept such that lhere a always a dnving heao of 0 6 m available curing the lean period to meet the maximum peak demand of irrigation The WOOL of the reservoir is at EL 1350.0 m ana accordingly the invert level of the ngtit bank imgabon out let has own fated at EL 134S 0 m.
114
Water Works Design & Supervision Enterprise
in Auotiaifon with latecnadauiial CtDioftuts and Tadutncrtu Prt Ltd.Arjo Detain [trtgiikn Projaei
D«n Appunenant Works
May2W?
An RCC duct of 1 5 m x 1.5 m square m seclion has been prowdeo to carrying tne discharge value of 7 52 m-’fsec The fnqban losses in the conveyance system have peen computed using Manning's equation Siaunchmg nngs to increase the seepage path have been provided at each pf the construction jcwit at 5m c/c interval m the impervious care downstream of comoi gate structure The RCC conduit section after the consmidKin, is back filled property to raise rt to the rep eievation of EL 136C 6 m The arrangement d! the imgabon out have oeen shown in the Drawing Mo. AD-F-DAM^
11.4 Irrigation Outlet for Left Bank Primary Canal
The irrigation outlet for the Left Sank Primary Canai have been located near the left abutment The alignment has oeen fixed much that the Rcc conduct of provided to irrigation pullet is m cut and cover section ano is aligned away for the downstream toe of the dam The Rcc duct section of 1 7 m * i.7m square shape has been designed 10 carry a discharge of 9.QIS m3rsec for meeting The water demand to imgatioh of the ieft bank primary canai The MDDL of the reservoir is at EL 1350 0 The inlet tavei of the irrigate outlet nas been fixed such that the duct is always carrying discharge 1o in the peak irrigation demand in tne lean season for this the iwet nas been nepi at a level so that there s always a dnvmg head of 0 6 m
The layout of the imgabon outlet and intake structure with a control gate i3 shown in the layout d rawing No. ACHP.rDAM/27 & 2B
11.5 Hydraulic Design of Irrigation Outlet
Right Ba nk Primary Canal
Location: Right Hank Saddle ha 2
Design Ducnarge proposed through this rrngaDon outlet as provided by irrigation group ■ 7 521 m’/aec to designing the irrigation outlet and providing a minimum head of 0.6m during the leanwl penod and ensuring the imgatran outlet discharges to meei the peak demand The velocity with the mimmun driving head of 0.6 m is computed by the relation
115
Witer Works Design & Supontetan Inurprise
In Assottatl-DD wtth tDleroottiiadla] Coosultaiiis and,Tecbnncrsts hft. Ltd*ijo   Dedeui   Irrigation   ProjBrt
Dun Appurtenant Works
Vtlooty ■ ^2 x h
- 3 43 m/Sec
Area of x-secbon tne of imgsfron oufiet required A’ ■ —
v
7,521
MjitZOOT
—;           Hifai
3.43
~2 19 sq m
Aocpbng g square duct of RCC of Mt 2.0 m * 1 5m for meeting the requirement of water
7 52 L
Area o! cross section requireo for discharge of 7.521 m3/sec is =
x-areg of X'section of the duct proviaeo *20*1 5 sq m
= 3 0 sq m
7 521 Velocity generated with inis area =            ——
• =2.19 sq m Area of
of cross section provided
Faction slope V = *5‘ ‘
H
A = 3sq m
P * 7m
-     2.507 m/sec
o
3
P7
R =0.57
w
V* —^—*10.57) 5”
0.016
355      35 5
2.5
" 35.5
q ■ 0.071
______________ _ _____________ __ ______________________________ _____________116
Water Works Design fc Supervision Enterprise tn IsMcliMan wilh IntettouUflenud Cfluuliints nd TecLtidcratn Ptl Lui.Mum Irrtf idao Project
Dim Appurtenifll Works
S- 1071}1
= 0 005
□r stope = im
Length of Due? = 1C0 * 105
= 205 m
MayZOT?
.               205
Head loss due to fraction - —
200
= 1.03m
The gate and groove tosses ar# assumw to be negligible
_ . oir
Entry loss = ——
2X
s Q_3x2.fi’
■ 2x881
■ 0 10 m
loss d neaa through Bw irasn raw is assumed negligible
r1
veooty head ai ent = —
2f
= 0.2x2.507*
2x9,81
= 0 06 m
Totai head loss = 1 03 + 010 + 0 06
■ 1.19m
say 1.20 m
Frf supply levels will be Kept below the leve> = 1350 -1 2 ■ 0.6 m
-1348 2 m
Bui Actual FSL provujed a 1348 0 m and n ok
The tap itvft of the RCC duct will be Kept at EL - 1348.00 - 0.15 tconstdenng Q 15 m depth
below canai FSL for dud to run hit)
= 1347 BSm
Bottom levei taking into account the thinness from EL: 1347.85
i.e 1347.85 '(0.5* 0.5 ’1 5)
- 1347 85- 2 5 ■ 1345 35m
_________________________________________________________________________________ 117 
Witer Works Design & Supervision Enterprise It Asodanon with totercnndDinuJ CaMuhuia ud Tachawrati Ptt Ltd.AjjG Ih dea» I rrtfitJMi PreJett
Dam Appurtenant Works
Depth c' water in me canal = 1 4 m (assumed) Canal level a 1346 00 -1 4 m
= 1348 40 m
JUyZMJJ
The general arrangement el layout plan end sectional elevation and other details of the imganon cxrUei for the Right Sank Primary Canai >s shewn m the Drawing No AD-F-DAW25 a 26
11.6  Hydraulic Design of Irrigation Outlet for
Left Bank Primary Canal
Location: At the left Afcutment near the crest of the aam
The discharge foe the irrigation outlet for left Bank Primary Canal as has been provided dy the mgaUon group has been considered for the design of irrigation outlet
Discharge = 9 02 m’rsec
WOOL of reservoir EL. 1350 00 m
Minimum Dnving head provided = 0.6 m
A cut and cover reinforced concrete duct is provided Im irrigation cut let from the reservoir Velooty v ■
= Vlr9Jiri>.6
’ 3 43nVsec
Area of doss section of the dud required for carrying the above discharge of 9.02 m3/$ec
902
=--------m/Sec
3.43
= 2 63sq m Provide RCC duct of size 1.7 mr 1.7m
X'SccOon area of the Rec duct -1.7xl7$qfn
■ 2 69 sq m
Water Wortai Dwlgn 1 SuperrUhn Enterprise
in UiocUtiflQ Till iataitMjtJBtnt*| Cmutuais TKhieenti Fvl LULArjft Detent Irrigation Project
Own Appurtenant Works
Actual ueiocrty of flow generated m the duct = —
_ w
= 2(9
e 3 12 fTu'wc Provide srfi level of the duct at = 13-50 - 0 6 -1 7
= El 1347 7 m Layout and alijnmem gftha ROC Square Dud
Miy 2007
Since tre ground level is nsing on trie downstream side of lhe dam abutment. rt is proposed to cake the irrigation outlet dud in excavation in rock The concrete duct wilt ne in straight alignment for the initial 18.0 m lengtn from the center ol control gate shaft and there after the Oud will M alined at an angle of 145° with the center line of the outlet and taken straight for
110.0m length The oud will then open out in the canal at a ground eievauon of about 1353 0 This point will be at d-stance of about 110 0 meter from the dam axis and snout 50 0 m away from the center line of the asm axis. A genergr layout ptan of the imgabon outlet ouct s snown
m the Drawing No AD-F-DAM/27 (, 28
A control gate operated Uy a hoist is prowled al the upstream of the gate shaft An emergency
gate on the upstream of the control gate ra provided for operation in an emergency situabon
The diameter of the control gate shaft housing for the control and emergency gate is proposed
to be of 8.0m internal diameter and centre of the weft snail be st a distance of 15 0 rr. from the
ms edge of lhe dam
v-312--KinS‘ri
a
Where
n ■ rugosity coefficient and is taken = 0 Q16
P ■ Welted penmeter of duct
A = Area of the cuct
S = Slope of lhe duct
1 7x1.7
* ?        4x1.7
- 0.425
__________________________________________________________________________________i 19 Water Worts Design & Saperrtslon Enterprise
Id i»od4iiofi wltls iBiermnUceDtil Consultants iDd Todmocnts PtL Lid.ArjoIMun Irrigation Project
Dim Appurtemt Works
R; ' =0.565
3.12 = —!— f 0.565 x S' ’
0.016
., , = 3.12*0.016
0.565
= 0009
S = 0 0070
Total length of tne over =20*110
= 130m
Lus? of head due to friction = 0.0070 x 130
-1.01 m
Adding 10 % for oenfl and turn x»S of head
Total ©ss* 1.10 m
The sill leva pn the downstream wilt be
■1347.7*1.10
= 13*66 m
F JI supply of canal assuming I 4 m deoth of water m the canai = 1346.6 + 1 4
■ 1348 00 m which is in order
Hay2M7
120
Water Works Design & Supervision Enterprise
In AsHdatton with InteroontlBsntxl Consultants ud Tectaocnu Prt LU*d«-D?dflss« IrrltatScn Project
Dam Appurtenant Works
Table 11.1 Aijo Dedessa Irrigation Project
May £007
Com^MWIon Gf 07M SpifeBy frofle
& ‘1 BS ■ 2 as- y
H O 2E2m
Upywi
fqc ^jQwnjiream peofi-e
Dowtuireiro
JL
Yi
XI            Yi
■OTO7
■OTC2 -O6A:
-owe
■oam
■06+2
-0629
■C.6O3 0.576
0.560 -0 524 O49B
-Q.472 -D.445
-0.410 -DM7
4J.314 43252
0210
-0157
-0106
■0.052 0.000
-0.310
■0.3C5
■0 206 -0 2K
-0 246
■0233
■0 219 -0.206 O 1«4
-&1W -0 146 O 129
•0 114 43lOl
■DM9
0.075
■OOM 0.041
-O.D28
■o.oia -0.010 43.KK
-0.001 0.000
OOOO'        0 000
0 250          0017
0500      >0 061
0 750       43 130
1 COO       •0.221
1 2M       •0 333
1 500       -0 467
1750      -0-62X 2 000        -0 795 2 250          -09U 2 $00        -1301 ??S0        -1 413 3000         -1 M3 3 250       -1 952 3 734       ■2.523
Tirnjtnl Pcwrt CwrdiMlfrt
TW ik?pf <X tfw floewwm gHas =0Ih 1V X J734 m CofTMponding V ■
m
-2 523
121
Witer Worts Design & Supervision Enterprise
tn taoctatton with Intmonttottial ComuIUhU ud Toctmoefati Pvt Ltd.Il "W*! lDj N3-LZ7I5
U            h&j 553«w-=uer.M’pDedust lrri£«iuD Project
Daim Appurtenant Works
12 HYDRO POWER GENERATION 12.1 Planning & Design for Irrigation
May 2007
The dam and appurtenani wonts have peen planned ana designed basically tc- providing imgabon in a gross command area of about 17 825 ha Hpcaiea on both tanxs ot river Dedessa downstream of the dam as required in the TOR of the Feasibility Study Accordingly the values for design decision variables, parameters and control levels have been finalized &s follows
Top iwHl of dam crest
EL 1380.6m
frl
EL  1356  0  m
MWL
MODL
EL 135B 6 m
EL 1350 m
FSL of Gina; on either sire
El 1348 m
Gross storage
1341  6  Mm3
Live Storage (between EL
-I356j
-
48549 Mm5
II  has  been  ocserved  Chet  enough  water  resources  are  available  at  the  aam  site  The  mean annual  flaw  rs  2328  Mm3    However  the  requirement  for  irrigation  in  final  phase  is  only  195 Mm3    But   the   requirement   of   FSL   in   the   canais   a   comparatively   high   m   order   to   provide imgatran  by  gravity  flow  Accordingly  the  MDDL  has  been  restricted  td  EL  1351m  only  though tn*  zero-eievation  after  the  drstnoutnn  silt  m  the  rasenrar  wonts  put  to  EL  1  US  m.  Therefore, live  storage  gniy  between  El   1358  to  1350  is  utilized  against  tatai  gross  storage  of  1341  6 Mm5.  With  these  control  revels  tne  required  success  m  terms  of  relrability  for  irngabon  protect is achieved
The  scope  of  increasing  tne  utilization  oy  expanding  the  command  area  has  ceon  ejramineo But rt has been found that there is no such scooe due to topographic features
122
Wttflt Works Design L Supc rTlslon Enterprise
| 3 JjiDrtadon with IqteTCC H One nlil Lonibltipts *mt Te tbu »  mis Pn. Ltd
cAijo Dadfsi* (rrt^stiDo Project
Dim Appurtenant Works
12.2 incidental Power Gerwration
May 2(W
The scope end possibility of power generation with the proposed design features have been esamirad Since (he canals are contour canafs with comparatively higher value for FSL there is very little difference between FRL of the rasmvolr and FSL of the canai Thu* lhera is op scope tor generation of hydropower from The imgation water ceiog released through me outlets However the scow ano possibility of generation of hydropower by releasing (he balance water of storage as well as water available through run-of-the-nver into the nver and locating the powerhouse near the river ceo have been studied For this the centerline of the turbine has oeen assumed at EL 1317m against the river bed of EL 132C and downstream normal water level of Ei.!323m The preliminary study indicates that a firm power of 5Mw can Oe generated with a5% reliability and tne power generation will ne 7Mw for 50% reliability However only 3Mwd nyttropower will be generated with 9S to 97% reliability
12.3  Generation of Opt!mum Hydro-power
As discut&ed above the utilization water for imgaLon is only 195 Mrn3 against the total annual availability of 239B Mm') Thus the site provides scope of harnessing the balance a variable water which w guile considerable, (or generation of power generation But t!i:S will require to increase the storage capacity by raising the height of the <iam aoove wnat has been planned for the requirement of irrigation only. Several tnai rune have been msoe for carrying out the simulations studies lor power generation by increasing the dam height successively These stori es indicate that with FRL increased to EL 1376 m (against the presently proposed FRL al EL 1356 m for meeting the requirement of irrigation wuyj. a firm power generation of 20 MW can t» achieved Assuming a toad factor of 0.6. tne installed capacity may be 33 33 MW Thus in order to harness the avertable potential tor hygro’powtr generation the oam height may nave to ot increased by about 20 m, which is quite ponsiaerabfe height and will require several major changes in the generBl HyOul and other design decision verubles and parameters
12.4     Need for Pre-Feasibility *mdy
In oroer k facilitate final decision about generation of hydro-power there is n&ea to undertake a predeasibility study to eataolisn the technical feMfajifty along with economic viability for namesstng me optimum power potential available at ttos Brte This study will take into
.123
Water Works Design i Supervlslo n Enterprise
io JLsacetittoawnti
uf TMtuncraxs ptl Ltd.Arjo Dedfliu lrrt<atiijn Prnjact
Dim Appurtenant Works
Maj 2007
considerations the location of the appurtenant works, along with increase in dam height and consequent increase in submergence The increase in dam height will require to relocate the spillway facilities. retocare the outlets on both-left A right - banks This will also require to raise the height of saddle dam The need or otherwise of any other saddle oam may have to be identified along with other aspect of submergence under the proposed reservoir Pre-feas bility study will ce awe address all these relevant issues and will facilitate the final divi$j on abom inclusion hyaro-power generation in the Project
{b.2j Power duration curve for FRL = 1356m - Option II
Fwntwrrt Fw*r to Equwltod or Ex c«« ocd, %
(b.3) Power duration curve for FRl • 1 J5Gm - Option III
Witir Works Design & Supervision Enterprise
In Association wtth itnertcntlaiinul Consuitaau and Technocrats Pvt Ltd.
124XrjcnDtiif55t inittTiaD Project
Dam Appurtenant Works
May 2007
B*w>At<»ri-Ai t*-Cipii2Jrj Cur*# for Arjo Dtoril# F**»FMok
,
i
Return ■ iM-'ilon Cw.Mji
Figure 12.1;
E/ewtfon-ArBa-Ci'jMcfiy Curves of Ago Dedesss ffittservou
L25
Waur Works Design & Supervision Enterprise
la AiMdlttau with LnureqijUtientil CiMuluuts utd TschnacriLi Pm LtdArjfrD! titifi intEitlon Project
Dam Appurtrnxnt Works
REFERENCES
1 Land and Wjter Resources of Blue Nile Basm 1964 by USSR
May 20d7
2          Preliminary Water Resources Ertvet&pment Master Plan for Ethiopia 1990 hy WAFCOS 3          Aboay River Basin Investigation Development master Plan 199S by BCEOM
fl 'design of Small dams' by United states Department of interior. Bureau of Reclamation
5
J
US Army Manual Eanfi Embankment EM 1110-2300' 3151 cmy 1994
6
US Army Msnuai Engineering and Design - Hydraulic design of reservoir cutlet structure
Engineering Manual EM 1110-2 - 1602 lit August 1963
7
US Army Engineer Manual EM 1110-2- 1603 Hydraulic design of SpiltwayS 3l" March
1965
? US Army Engineer Manua. Engineering ana Design Stability of Earth and Roc* fill Cams
EM 1110-2-1902151 April 1970
9
ICOLD-1994 Embankment Dams - Granular Fillars ano Drams - Review ano
Recommendaljan
10
Sneram JL, Dunnigan lP and Talbot JR 1984 (a) Basic properties of sand and granuiar
filler^ journal <jf Geolecr.nics, Engineenng ASCE
11       Sberard JL Wood ™d RJ  Gieoenski SF- "Earth ano Roon fill dam"
h
12. Thomas M LEPS, Rock fill Dam Design and Analysis
13        Report of Geopnys»cai Observatory Addis Ababa University Ethiopia dt June 29. 2006
14        Earth quake History of Ethiopia and Hom gf Africa by Pierre Gcum Director of Gwpnystcal observatory University of Addis Ababa. Ethiopia (1957-7B)
15          Robn   Fell,   Patrie*   M*c   Gregory   and   Dawn   Stapleaon   -Geotecnmcal   Engmeenng   of Embankment DamsH
16. Indian Stannard Codes
i) IS 6626 -1976" Guide Lines for design of targe earth ana rock (ill dams -
<) IS 10635. 1993 ’ Guldelin«-Free board requirement m embankment dams"
Hi) IS 7894 -1975
.-------------------------------------- ---------------------------------------------------------------------------------------- 126 Waur Works Design 1 Superrtslon Enuurprist
[L kJSbCtHLOtt WtU InLerenuBBeaul ConmlLanb lad 7« Hr,5Cr>U hr Ltd*rtoDtide is* con Project
Dim Appurtenant Works
May2AOT
hf) IS im -1984 Catena far earth quake resistant design of structure (TWd Edibon)
v) IS 6934-1973
vil IS 1S51B8 - 1994 "Criteria for Design of Cnute spillways”
*•> IS 14815-2000
wiij (S 7500 - 2000 "Coae uf Practice far installation anti observation of cores anu fcr measurement of internal vertical Moment m Earth Oams (First RevESi.on}"
ix)    IS 9429-1999 Tootle of Practice Drainage System For Earth ano Roc3< fill Dam- First Revision"
x)   IS 7356 (Part-1) - "Code of Practice Tor installation, maintenance and observation of Instruments lor pore pressure measurements m Dam & Roon fill dam"
xi} IS t2200' 1987 "Code of practice for provision of water slops out transverse contraction joints in Masonry ana concrete oams"
127
Witw Works Dealpi & Supervision EaHflfpris t laAuHUtferi with Intett&ndDemii CmiitMti and TMhnwmts Prt UdArje Deden* lrrtfttion Project Dim Appwtfitiint Wortj
Project Ar7° ’ &♦<*•••■ Irrlg^kMi Feeelblllty
■ludy
Cknl J- BBrilrtry OfWttW Reeourcee
LoceBon:- Arjo Deweese Object :* SelleerRplee
1 Soli eemplee
M*y2OO7
LAMFWOflY I£3T Witt OF CUAY »AMPUE
Grain etie
dlitrfoution
G««v*n3Md
Atterberfl limit
Compectkm
Sheer ■trangth
r
Lociflo* O<
Bore bole
Depth kn
Specific
Brevity
%
%
Fine
%
LL
IM
PL
CM
PI
JM
Free
Swell
IM
llneer
v hr Inhere
CM
Nitunl m(%L
OMC
%
MOD
kgiml
PffmeeblBty
cnVtec
c
KNrm2
□
DEG.
C
KMIm2
,1
DEG.
4effUf*«
i
ATB TP 1
0 25-0 M
2 70
0
2
98
64 20
138 00
26 20
80
-
*
-
-
?
ATB TP 2
0 20-0 90
3.M
.0
7
93
6060
34 80
26 00
40
*
-
-
a
_
r3
ATB TP 3
0 20-2 10
l.M
0
1
IM 20
38 10
30 10
50
5 ID
34 89’
1340
4 61*10*~
-■
-
1
4
ATB TP 4
010-080
2.58
-
-
62 6C
•3860
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Dim Appurtenant Wort*
LABORATORY TEST RESULTS OF SAND SAMPLE
2 Sand Semple*
May 2007
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Water Works Design & Supervision Enterprise
in AHKlitfoB wllll lntercwitisssl-1 amounts Md Teehnornti Pvt HiDim Appurtenant Works Laboratory T«t result of Rock Sample
May 2007
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Tested by
Date
Checked by
Date
Getachew and Mulu
30/07/06
Abrahma Assefa
30/07/06
Date
Water Works Design & Supervision Enterprise
In Association with Intercontinental Consuftanta and Technocrats Pn Ltd.Dale Due
AUTHOB
rrTil
call no.
edition
VOLUME
CA«. no.

Summery

Arjo-Dedessa Irrigation Project Summary

Arjo-Dedessa Irrigation Project Feasibility Study Report

Volume III(b): Dam and Appurtenant Works

Project Overview

The Arjo-Dedessa Irrigation Project involves the construction of a 40.6m high earth and rock fill dam on the Dedessa River in Ethiopia. The project aims to provide irrigation for approximately 13,655 hectares of land and includes potential for hydroelectric power generation.

Key Components:

Earth and rock fill dam with central impervious clay core
Chute spillway on the right flank
Two irrigation outlets (right and left bank)
Reservoir with 1341.16 Mm³ storage capacity at Full Reservoir Level (FRL)

Dam Specifications

Parameter	Value
Type	Earth and rock fill with central impervious clay core
Height above river bed	40.6 m
Crest length	512 m
Crest width	10 m
Upstream slope	2H:1V (to EL 1340.6), then 2.5H:1V
Downstream slope	1.5H:1V
Top elevation	EL 1360.6 m

Reservoir Characteristics

Parameter	Value
Catchment area	5,278 km²
Maximum Water Level (MWL)	EL 1358.60 m
Full Reservoir Level (FRL)	EL 1356.00 m
Minimum Draw Down Level (MDDL)	EL 1350.00 m
Storage at FRL	1,341.16 Mm³
Active storage	466.49 Mm³
Dead storage	874.67 Mm³

Key Design Aspects

Geology

The dam site features fractured and vesicular basalt rock formations. Extensive grouting is required due to high permeability values (up to 54 Lugeon) in some areas.

Foundation Treatment

Cutoff trench extending to firm rock foundation
Curtain grouting (two rows in valley, single row in abutments)
Consolidation grouting to 10m depth

Construction Materials

Material	Source Locations	Key Properties
Clay core	5 borrow areas (Ate, Chewe, Dhendessa, Maribo, Obose)	High plasticity (LL 56-67%), permeability 10⁻⁴-10⁻⁶ cm/sec
Rock fill shell	ADSHQ area (3km downstream), Guche area	Unconfined compressive strength ~30,375 kN/m²
Riprap	Buketa and Colisin quarries	Unit weight 2,761 kg/m³, abrasion 31.5%

Spillway

Type: Ungated ogee chute spillway
Location: Right bank saddle
Design flood: 1 in 10,000 year (1,965 m³/s peak inflow)
Width: 125m
Maximum surcharge: 2.62m

Instrumentation

The dam will be equipped with monitoring instruments including:

Piezometers (17 in foundation, 24 in embankment)
Surface settlement points (22 locations)
Seepage measurement weirs
Seismic accelerographs

Construction Approach

The project will be constructed in phases over approximately 4 years, including:

Initial cut-off trench excavation and RCC diversion duct construction
Main cofferdam construction (to EL 1340.6)
Dam raising and spillway construction
Final completion and plugging of diversion duct