free- 35/
ETH/88/013
Government of Ethiopia
Water Resources Development Authority
BALE GADULA IRRIGATION PROJECT
Annex D
Geological and Geotechnical Report of weib Diversion Weir by
Anania Abay Theodros G/Egziabher
United Nations Development Food and Agriculture Organization cf
F rogramme 
the United Nations
Addis Ababa
June 1992CONTENTS
1.
INTRODUCTION
2.                      GEOLOGY AND GEOMORPHOLOGY 2.1       Geomorphology
2.2
Geology
2.2.1                Basaltic Formation 2.2.2                Soil Formation
3 .                     GEOTECHNICAL FEATURES OF THE FOUNDATION 4 .                     CONSTRUCTION MATERIALS
4.1
4.2
4.3
Coarse Aggregates Sand for Concrete
Earth Lining Material for Canal
5 ,                     CONCLUSIONS
ANNEXES
Geological Section of the Foundation Eoreholes logs
Test pits logs Laboratory results. Location mapI.
INTRODUCTION
Th»     Bale     Gadula     Irrigation     project     in     located     about     95     km     ftom Gob*      in      Goro      Awtaja      (Bal*      Region),      about      520      km      anuth-eaat      of
Addis Ababa between v b' Q‘ latitude and 40” 1R' to 40” long!t nd*
J7'
Th^      Irrigation      aiea      (ftint      phaee)      la      aituaied      on      the      left      bank ot      Weyib      live:      bounded      by      the      ilvei      from      flouth-Weat,      Kuban      village from     the     west     and     the     Aaaendabo     dry     atioam     from     north     and     north east For this phase only a diversion weir will be needed.
The      height      of      the      Diversion      weir      is      about      1.5m,      with      the purpose to irrigate about 550 ha.
Geological and
weyib river
geotechnical        investigations        were        carried        on        the
basin from Dec.
31, 1991 to Jan 24, 1992.
At the
depths:
weir      axis      three      boreholes      were      drilled      to      the      following 
BH-1                 12m EH-2                9.20m BH-3                 7.20 making      a total of 28
. 40m
In the        command area        four
boreholes        were        drilled        to 
det
ermine
is
about
along
the
the       thickness       of       soil       formation,       the       shallowest       borehole
3.23m and the deepest is 8.35m.
In      addition      ten      hand      dug      pits      have      been      excavated 
mam canal to  a depth  of 3m. This helps in  adopting  proper methods if excavation  and  determining  the engineering  properties of the excavated materials which will be used as construction material.
Samples      have      been      collected      from      the      hand      dug      pits      for      the following laboratory tests:
Grain size Analysis Atterberg limit Proctor compaction Shear strength
12.
GKQLQGY AND GKOMORPHology
2-      SEQMQRPHOLOGY
1
The project area is
surrounded by hard formati
located       on       the       Weyib 
river
valley 
Basaltic rock, outcroppin 
on    of    the    Trap    series    of
lava
of    the
river stream.
9 on both sides of the valley and
Starting  from the bottom mountains there is a thick  layer cotton soil dips with a gentle
of the sides of the chain 
of colluvial deposit of Black slope to the river stream.
Generally       Weyib       river       follows       along       a       fault       line
which
has a general direction N100°W or S80°E
Since      most      of      the      catchment      area      is      covered      with      forest there is no high sediment transportation into the reservoir.
2.2 GEOLOGY
2.2.1 Basaltic Formation
The       Easaltic       rock       is       formed       in       Tertiary       period,       as       a Trap-series        of        lava.        This        dense        Black        rock        with        vesicular texture,      is      outcropping      on      both      sides      of      the      valley      and      river stream.
On      the      surface      of      the      rock      appears      a      joint,      which      has beer,     formed     due     to     shrinkage     on     the     cooling     of     the     magma.     In- addition        the        appearance        and        disappearance        of        vesicles        every few     meters     in     depth,     shows     the     flow     of     the     lava     was     a     repeated process.
Generally,        the        similarity        of        rocks        outcropping        on        the river     stream     and     few     places     of     the     command     area     on     both     the left        and        right        sides        of        the        valley,        in-addition        to        the topography      of      the      area      shows      there      was      displacement      due      to faulting.       But       there       is       no       indication       of       active       faulting       at present.
2.2.2
valley. The soil can -------------------------------------- on the mode of formation. The color
Soil Formation
A thick soil formation covered a
be      classified 
large       area       of       the as      a      Residual      soil,      based 
nioae       or       location.       The       color       varies       from       black       to 
brown,
dries up with small cracks.
the Blacki —•sh --s-oi --l--s-w--e--l-l-s-e--normously when wetted and
23  ’ GZOTECHNICAL FEATURES OF THE foundation
means^of drVlV’h i
f           d*111           ^oles,       and       the
l0n9 the ax*s were
carried out by
data       collected       fror       th=
boreholes assisted  in  preparation  of the Geological Section 
o. the foundation  and  in  evaluation  of the engme=rinc
properties of the foundation.
From top to the bottom of the Geological section is:
^yiae-rmg
a.             Dark     brown,     clay     with     abundant     grass     roots,     1.1     64     and Pi      36,      imperivous      soil,      classified      as      Highly      plastic      clay (CH) .
b.             Fine    to    coarse    clayey    sand    with    Gravels    classified    as    GC, permeability coefficient K=1.45xl0'4 cm/s.
Vesicular Basalt, highly  jointed, vesicles filled  with calcite, permeability  coefficient evaluated  in  the bore holes by means of packer test, the value K=10’‘ to 10‘ m/s
7
4. CONSTRUCTION MATERIALS
4 .1 Coarse Aggregates
The      bottom      of      the      hill      is      covered      with      cobbles      and boulders      which      have      been      transported      from      the      hill      due      to gravity.       It       is       possible       to       use       them       as       a       source       for aggregates.       In-addition,       both       sides       of       the       valley,       which       are very near to the weir site can be used as a quarry sites.
4 . 2 Sand for Concrete
As     mentioned     on     the     report     prepared     by     the     Korean     team, the    only    source    for    sand    in    Toggona    river    74km    from    the    weir site just near Robe town.
According      to      the      laboratory      results,      there      is      35%      fine to     coarse     sand     and     65%     fine     to     medium     Gravel     (poorly     graded sandy Gravel).
4.3 Earth Lining Material for Canal Section
Along    the    main    canal    ten    hand    dug    pits    were    excavated    to a      depth      of      three      meters,      to      evaluate      the      sub-surface-of      the main    canal.    At    Test    pit    No    1,    No    2,    No    3,    No    4,    No    7,    bed rock was encountered at depths, from 2.00 to 2.90m.
According      to      the      laboratory      results,      the      soil      taken      from test       pits       is       classified       as       impervious       highly       plastic       clay, with    L.L    ranging    from    64    to    130    and    P.I    ranging    from    24    to 100.
3Six 
modified 
compaction 
tests
were
carried 
out,
and 
the
value
of
MDD
are      between 
1.2 
and 
1.47 
g/cc
with 
the
corresponding value of OMC between 27% and 39%.
On the same, sample strength tests have been carried out to determine the effective angle of internal friction and
cohesion.       The       results       are:       PHI cohesion ranges from 0.78 kg/cm2
ranges     from     3.37° to 1.82 kg/cm .
to 15.83s,
2
5.        CONCLUSIONS According to the
data        collected from
the bore
holes,laboratory results and Geological surveying it is
possible to give the following conclusions:
The      selected      weir      site      is      suitable      from      the      geological point of view, and since the bed rock is at a
suitable     depth,     the     weir     can     be     founded     on     strong     bed rock.
Since     the     joints     decrease     with     depth     there     is     no     major risk on the weir foundation.
The     nearness     of     the     quarry     site     to     the     project     area     with unlimited quantity of stones is one of the advantages.
Since the workability  is poor and  volume change is critical of the material excavated  from the canal, some design  consideration  must be given  to  use as earth  lining material (if necessary).
4Il
h
BORING LOG
PROJECT: WEYIB DIVERSION WEIR
LOCATION:
DORTNC
N°:
b.H.1 
ELEVATION (mt*.)
WATER DEPTH (mts.) 6.00m
C,XS INC: N
W
CORE BARREL TYl’E: DOUBLE (NQ,BQ)
BIT TYPE: DI AMY
li
ft
R£( ?0\
/ERY
t
—1            o
M
M
H  0  D
r
In
DESCRIPTION
IN SITU
O.E.T
*
*
K=
1.45x10
cm/s-
>-A
5rr-
L
t
|
u
•
a
J
1
to
*
1
1 ■0L
Dark brown clay, Medium
plastic, abundant roots.
1.80m
Fine        to       coarse       clayey       sand 
with Gravells
3.70m
From 3.70 to 4.65 Highly vesicular
T               Basalt, with vertical to sub-vertical joints, filled with fine materials.
)■
la
--
L■
P*a
—
EL
■
ij
L
’*>''
T~
i;
$,
$
-*
■-
..
r
= i
•• r-
j'
F!
K=3.3xlC' m/s
K=8. 78xlC I
1
1
From 9.40m to 12.00m Highly vesicular Basalt, and vericles are not filled,
sub-vertical joint, spacing 20 to 50cm
12.00m
i
*
0
15
16
1 7
1 b
19
20
*
23
Jboring log
PROJECT: WEYIB LOCATION:I
BORING LOG
PROJECT: WEYIB
LOCATION:
BORINC N°: B.H.3
ELEVATION
WATER DEPTH (mts.) 1.55
CASING: NW (0=7 6mm)
CORE I1AHHEI. TYl’E: DOUBLE (NQ,BQ)
BIT TYPE: DI AMYWEYIB
IRRIGATION PROJECT
SITE:                   .VlS .W1! .Sanai....................
TEST PIT NO. . k.............................
LOGGED   BY:                                                                                APPROX. COORD...
./...............
I^PTH
DESCRIPTION
SAMPLES
0:5
Black, plastic clay with abundant grass
1 —
Light grey, silty cl^y, with
Concretions. CW
1.50
2-----
-ight grey, sandy-silty caly
With concretions
2.80
3----
Bed Rock
4
AnCe
. l° §  ^ Main Canal
TEST PIT NO
... .................................
APPROX. COORD............................. /..............
2
LOGGED MV •
DEPTH
DESCRIPTION
SAMPLES
Black, plastic clay with 
abundant grass roots
»
1—
1.76m
2----
Brown silty clay with 
Concretions
3-----
3.163
Bed RockVEYj'B
SITE: A\°.nA 5?.e. ^in Canal
LOGGED BY:
IRRIGATION PROJECT
DEPTH
DESCRIPTION
Black, plastic clay with Abundant grass roots
TEST PIT NO.................................................................................
APPROX. COORD......................................................... SAMPLES
1.50
^Jrggn clay with concretion Bed rock
SITE: .Along  • .he i
LOGGED BT:
DEPTH
e
Main.Canal    *..
DESCRIPTION
Black, plastic clay with abundant grass roots
TEST PIT K):•••
APPROX. COORD/....................................................................
SAMPLES
1.26m____________________ _____________ Brown, plascic clay with 
abundant concretions 2.40m
Bed Rock *WEYIB
IRRIGATION PROJECT
SITE:                                                                                                      TEST PIT NO. ...      A .................
LOGGED   BY:                                                                                  APPROX. COORD...
/..............
‘depth
DESCRIPTION
SAMPLES
—
Black, plastic clay with 
abundunt grass roots
1 —
1.32m
brown clay with concretions
1.75
2—
Bed Rock
3 -----
SITE •
LOGGED BI:
.V1.® .Canal b # o.
TEST PIT NO................................. ?.......................... ....
APPROX. COORD.................................... I..............
DEPTH
DESCRIPTION
SAMPLES
Black, plastic clay with grass roots
1
2
1.62m
Brown clay with few concretions
2.70m
Bed RockWEYIB
IRRIGATION PROJECT
SITE:     . Alppg.               tviA Canal. ...
TEST pit no. ...         7.... .. ....................................
LOGGED   BY:    .................................................. APPROX. COORD...
/
•h     -
u
DEPTH
DESCRIPTION
SAMPLES
1 —
Black, plastic clay, with 
abundant grass roots
2 -------
2.30m
—
3 -------
Brown clay, with few concretions
2.95m
Bed rock
SITE:..^PPg.CV§.^iQ.C«u«l, LOGGED BY:
TEST PIT HO
APPROX. COORD
DEPTH
DESCRIPTION
SAMPLES
Black, plastic clay, with 
abundant grass roots.
Brown clay with lew concretions
3.0?)n
bed rockWEYIB
IRRIGATION PROJECT
SITE:
Along the Main canal
tf^t ptt nh                     5
LOGO ED BY:    .................................................... APPROX. COORD
/..............
DEPTH
DESCRIPTION
SAMPLES
1 —
Black, plastic clay, with 
abundant grass roots.
2 -------
2.30m
—
3
Brown clay with few concretions
3.00m
—
SITE:.
Alone the Main Canal . __ 
rp.ST PTT MO.. - -19.........................
LOGGED    BY:
.............................................................. APPROX. COORD...
DEPTH
DESCRIPTION
SAMPLES
»
1 -------
Block, plastic clay, with
abundant grass roots
and few gravels
2------
3------
XOO
bed rockW.R.D.A..SOIL-MECHANICS,LABORATORY PROJECT,ETHIOPIA
SHEET NO.1
.A80RAT0RY TEST RESULTS.bale.gaiwla
—
—
—
15/APKlL/yz
nnAru C17C nTCTDTDIITinM t PASSING
_________ —----------------
4.75t0 |      19.1 t     u ABOVE
A Jierberg.limits.
0.075 tol 0.425 t| 2 to 0.425 mm] 2 mm • .4.75
LL      PI        SL
LAB.
NO
FIEL
IDENTIFICAf
TION
)
DEPTH
(m)
BELOW            0.002 to
19.1mm 1    76.2mm
76.2mm % %
-J
UNIFIED
SOIL CLASS IFICATION
)
CLAY
SILT
Sand
GRAVEL
CPBBtE
GS
f              Im                      1 c
F
C
1
39b
TPi
0.5 - 1.5
34
33
33
64
36
2.77
CH
3*6
TP j
1.5 - 2.9
2 (
41
57
64
37
2.71
CH
397
TP 2
0 - 1.76
70.2
25.67
4.13
91
56
2.75
CH
397
tp2
1.76-3.16
70
16
14
82
56
2.76
CH
>
398
tp3
1.5 - 2.0
32
30
38
43.4
24.3
2.69
CL
■
399
tp4
1.26-2.4
50
42
8
74
52
2.71
CH
400
tp6
1.62-2.7
60.5
29.9
9.6
124.5
87.5
2.64
CH
401
tp7
2.3 -2.95
80.2
15.68
4.12
133
89
2.62
CH-ABORATORY TEST RESULTS.^ .U4QUU.........................
W.R.D.A. SOIL MECHANICS LABORATORY
PROJECT,ETHIOPIA
15/APRIL /92
REF MO.00002/92 SHEET M0.1
GRAIN SIZE DISTRIBUTION I PASSING
........... ...............................A
Kerberg limits
UNIFIED
J
LAB.
NO
FI ELI
IDENTIFICA'
TION
)1
DEPTH
(m)
BELOW
0.002
0.002 to
0.075 mm
0.075 to 0.425 mm
0.425 tf 2 to
2 mm 1 4.75
4.75to
19.1mm
19.1 t 76.2mm
i ABOVE 76.231a
LL
%
PI
X
SOIL   Ci-ASS IFICATION
CLAY
SILT
!>and
F
M              1C
GRAVEL
F
i
C
CPBBtE
SL
%
GS
402
tp3
0.95-2.45
70.5
25.19
4.31
127
87
2.7
CH
402
TPg
2.45-3.0
80. 'l
17.9
2.0
150
107
2.72
CH
i
403
TP9
0.45-2.3
70.9
27.98
1.12
102.‘
61.3
2.69
CH
403
tp9
2.3- 3.0
85
12.5
2.5
131
97
2.70
CH
ILASUkjlORY TEST RESDlTS^bale.gadula
UihoistjruEu/juturjed cample
W.R.D.A SOIL MECHANICS PROJECT,ETHIOPIA
15/APRIL /92
SHEET NO.t 00002/92
Er.
NO.
Laj
NO.
SOIL
CuASSir iCATIt’ 1
(m)
iWC
IiMSITUF
STRtN,’H TEST 01
R/TRI
SP.gr
OMC
z
MOD
g/cc
TOTAu stress
ErrECTIi'l   ■ STRESS
c,
Kg/cmz
0
o
C‘
p”
CONSOLIDATION
\ DATA
REMAIK
1
390
TP!
(0.5-2.9)
I 29
1
1.46
1.67
9.59°
_______
2
391
tp2
(0-3.16)
______
31
1.32
0.70
15.83°
i
3
392
tp4
(0-2.4)
27
1.47
1.82
8.21
4
393
tp6
(0.8-2.7)
38
1.2
1.15
3.37
5
394
TP 7 
(0.85-2.95)
39
1.22
1.15
4.35
j
6
395
tp9
(0.99-3.0)
37
1.21
1.56
7.5per; passing
.075 1
-LAY
SIEVE N°/SIZE
Medium
SAMPLE N*
DEPTH-M
CLASSIFICATION
poorly graded
PROJECT
Gravelly sand
Saoi£le_DQfB_ 
Sadmitted 
by 
Report Na
I.
GRADATION CURVES
Plotted
Checked
Date of Repor
t ^hi of^U^hTab^fofy
efSUD AN
FIGURE I PROJECT LOCATION
Z■\
1
Notitnoi Boundary
•
\
+ vT
)
1
\
I
Rood
\ '•
Rdilrwd
SOMALIA
BALE GADULA
PROJECT STTE
MOGAD6H0
UGANDA

Summery

Bale Gadula Irrigation Project Summary

Bale Gadula Irrigation Project - Geological and Geotechnical Report Summary

1. Project Overview

Location: Approximately 95 km from Goba, in Goro Awraja (Bale Region), about 520 km southeast of Addis Ababa (7°6'-7°9' latitude, 40°17'-40°18' longitude).

Purpose: Diversion weir (1.5m height) to irrigate about 550 hectares on the left bank of Weyib River.

Investigation Period: December 31, 1991 to January 24, 1992.

2. Site Geology

2.1 Geomorphology

Located in Weyib River valley surrounded by basaltic rock formations
Thick colluvial deposits of Black cotton soil with gentle slope toward river
River follows a fault line (general direction N100°N or S80°E)
Low sediment transportation due to forested catchment area

2.2 Geology

Basaltic Formation:

Tertiary period Trap-series lava
Dense black rock with vesicular texture
Joints formed from magma cooling shrinkage
Evidence of faulting but no current activity

Soil Formation:

Residual soil varying from black to brown
Blackish soil swells when wet and cracks when dry

3. Geotechnical Features

Foundation Stratigraphy:

Dark brown, clay with grass roots (Highly plastic clay - CH)
Fine to coarse clayey sand with gravels (GC)
Vesicular Basalt (highly jointed, vesicles filled with calcite)

Permeability:

Clay layer: Impervious
Sand layer: K=1.45×10^-4 cm/s
Basalt: K=10^-6 to 10^-7 m/s

4. Construction Materials

Material	Source	Properties
Coarse Aggregates	Bottom of hills (cobbles/boulders) and nearby quarry sites	Unlimited quantity available near project area
Sand for Concrete	Toggona River (74km from site)	35% fine-coarse sand, 65% fine-medium gravel (poorly graded)
Earth Lining Material	Excavated from main canal (10 test pits)	Highly plastic clay (CH) with LL 64-130, PI 24-100

Compaction Test Results:

MDD: 1.2-1.47 g/cc
OMC: 27%-39%

Shear Strength:

φ': 3.37° to 15.83°
Cohesion: 0.78-1.82 kg/cm²

5. Conclusions

The selected weir site is geologically suitable with bedrock at appropriate depth
Jointing decreases with depth, minimizing foundation risk
Abundant construction materials available nearby
Excavated canal material requires design consideration for use as earth lining due to poor workability and volume change characteristics

Investigation Details

Boreholes: 3 at weir axis (total 28.4m), 4 in command area (3.23-8.35m depth)

Test Pits: 10 hand-dug pits along main canal (3m depth)

Laboratory Tests: Grain size analysis, Atterberg limits, Proctor compaction, Shear strength