FEDERAL DEMOCRATIC REPUBLIC OF ETHIOPIA MINISTRY OF WATER RESOURCES ERER DAM & IRRIGATION DEVELOPMENT PROJECT Final Detail Design Report A lmi*. D-iisiqr. May. IExecutive Summary Volume I: Dam & Appurtenant Structure Annex A: Dam Design Annex B: Dam Appurtenant Structures Annex C: Geotechnical Study Annex D: Hydrology Volume II: Irrigation & Drainage Annex E: Irrigation & Drainage Design Annex F: Road Infrastructure Annex G: Project Control Centers Annex H: Operation & Maintenance Manual Volume III: Project Worth AnalysisTable of content 1.0 Introduction............ .............................................................................................................................. 1 1.1 General................................................................................................................................................ 1 1.2 Location and access to dam site............................................................................................................1 1.3 General description of major work components................................................................................ 1 2.0 Type of Dam............................................................................................................................................ 2 3.0 Seismicity................................................................................................................................................ 3 4.0 Diversion Arrangements........................................................................................................................ 3 4.1 General................................................................................................................................................. 4 4.2 Design Data........................................................................................................................................... 4 4.3 Design Flood for Diversion..................................................................................................................4 4.4 Diversion Channel Design................................................................................................................... 5 4.5 Closure of Gap..................................................................................................................................... 6 5.0 Dam Heights Reservoir Levels.............................................................................................................. 8 5.1 General................................................................................................................................................. 8 5.2 Dead storage Level...............................................................................................................................9 5.3 Minimum Draw Down Level (Mddl).........................................................................................................9 5.4 Full Reservoir Level............................................................................................................................ 9 5.5 Maximum Reservoir Level.....................................................................................................................13 5.5.1 Elevation-Storage-Outflow Data...........................................................................................................13 5.5.2 Inflow Hydrograph.............................................................................................................................. 13 5.5.3 Results of Reservoir Routing.............................................................................................................14 5.6 Top of Dam Embankment (Dam Crest Level).........................................................................................15 5.7 Freeboard............................................................................................................................................ 15 5.7.1 General................................................................................................................................................. 15 5.7.2 Calculation of Normal Free board:...................................................................................................... 16 5.7.3 Settlement due to strong Ground Motion............................................................................................. 20 5.7.4 Dam Crest Level or Top Bund Level (TBL):....................................................................................... 20 5.8 Height of the Dam................................................................................................................................ 20 5.9 Significant Levels.................................................................................................................................20 6.0 Various components of Embankment dam............................................................................................. 21 6.1 Crest Width......................................................................................................................................... 21 6.2 Camber/ settlement allowance............................................................................................................22 6.3 Parapet wall........................................................................................................................................ 22 6 4 Guard stones.........................................................................................................................................22 65 Berms..................................................................................................................................................... 22 6.6 Impervious Core................................................................................................................................... 23 6.7 Shell Zones.......................................................................................................................................... 23 6.8 Cutoff.................................................................................................................................................. 24 6.9 Rock Toe.............................................................................................................................................. 24 6.10 Toe Drain.............................................................................................................................................. 25 6.11 Upstream Slope Protection.................................................................................................................25 6.12 Down Stream Slope Protection.......................................................................................................... 27 7.0 Stability Analysis of dam....................................................................................................................... 28 7.1 General.................................................................................................................................................28 7.2 Material Properties Considered for Analysis......................................................................................28 7.2.1 Material in Impervious Core................................................................................................................... 28 7.2.2 Material in Shell zones..................................................................... ...................................................... 29 7.3 Loading Conditions.............................................................................................................................. 31 7.4 Minimum Factor of Safety...................................................................................................................31 7.5 Stability Analysis.................................................................................................................................32 8.0. Geology along dam axis............................................................................ ■.......................................................... 34 9.0 Foundation treatment............................................................................................................................35 9.1 Surface Treatment............................................................................................................................... 35 9.2 Subsurface treatment.......................................................................................................................... 36 10.0 Internal Seepage Control Measures.................................................................................................... 3810.1 Transition Filter I Inclineo filter........................ .-............................................-.......... -....................38 10.2 Horizontal Filter-................................................................................................................................... . 39 10.3 Special Seepage Control Measures at Contact with Steep Abutments....................................... .........40 11.0 Dam Instrumentation.............................................. ................................................................. —40 11.1 General.'.......................................................................................................................................................... 40 11.2 Instrumentation Scheme.................................................................................................................... .......—42 11.2.1 General Scheme................................................................................................................................... -.42 11.2.2 Measurement of Pore Water Pressures-..................................................................................................42 11.2.3 Measurement of Internal Movement-..................................................................................................... 42 11.2.4 Measurement of Surface Movements-................................................................................... .............. 43 12.0 Bill of Quantities, Cost Estimates and Tentative Construction Schedule.............................................. 43 12.1 Dam Appurtenance Works........................................................................................................ —43Ercr Dam & Irrigation Project /CECE & CES 1.0 Introduction 1.1 General Erer Dam is one of the major components of Erer Irrigation Development project. This is basically a storage dam across river Erer to utilize the annual flows of the river for the purpose of irrigation development in its command area. Three alternative dam sites (dam axes), including the one selected during pre-feasibility study, were studied in detail to decide most suitable site from techno-economic considerations. Option III has unfavorable geological set-up and has a longer length. Option II has comparatively weaker foundation for locating spillway and spill channel and without any specific attractive features Thus option I was found to be best suited for locating the dam and chute spillway structure. The orientation of dam axis has been fixed taking into account the topographical configuration of ridge on left and right abutments. The selected axis is aligned exactly in East-West direction; the coordinates of reference point AR lying on the dam axis are 1028361.961 North, 195963.404 East. The total length of dam is about 1460m, excluding 30m crest length of spillway The maximum height of dam above deepest river bed level is 36.6m. 1.2 Location and access to dam site The dam site is located at about 6km upstream of the bridge across Erer river on Harar to Jijiga road The site is about 25 km from Harar and 17km from Babile towns respectively Location plan of the dam site is furnished below vide Fig 1.1 1.3 General description of major work components • A zoned earthfill dam 36.6m high above deepest river bed. • An irrigation outlet with intake tower through right abutment • A chute spillway with ogee crest located on the left bank • River diversion work. Annex A : Dam Final Detail Design Report/ 2009 1Erer Dam & Irrigation Project /CECE & CES 2.0 Type of Dam Based on the bore holes drilled at the dam site, the thickness of the overburden at the river bed portion is found to be around 19m followed by crystalline gneissic rock. The overburden is mainly characterized by about 7m deep silty clay, sand mixed with gravel spreading all along the axis of the dam. But in the river bed portion it is underlain by about 11 m deep coarse gravel and cobble mixed with sand. The length of the crest of the dam is about 1.46 km and the site falls in high seismic prone area In high seismic prone area, the earthfill dam or earth and rockfill dam is always preferred due its flexibility than to have a rigid structure like concrete dam. Now considering huge overburden, large length of the dam and seismicity of the area, the site is found not fit for construction of concrete dam The site appears ideal for construction of either Earth dam or Earth and Rockfill dam. Since adequate quantity of suitable earthfill materials are available from different borrow areas at site, it is decided to go for a zoned Earth dam. Annex A Dam Final Detail Design Report/ 2009 2Erer Dam & Irrigation Project ZCECE & CES 3.0 Seismicity The dam site is considered to be falling in zone IV of seismic zoning map of Ethiopia. It’s the zone of major damage in which seismic ground shaking is said to be producing intensities VIII and above. For not having any site specific ground motion record and information, seismic co efficient of the area is compared with the zone IV of seismic map of India, for which the basic horizontal seismic coefficient (do) is 0.05 In seismic coefficient method as per Indian standard the design value of horizontal seismic coefficient cth = P I ao Where p = a coefficient depending upon the soil foundation system. The value of P for all types of dam is taken as 1.0. I = a factor depending upon the importance of the structure. For all types of dam, the value of 1 is taken as 3.0 do = basic horizontal seismic coefficient The horizontal seismic coefficient (Oh) thus comes to 0.15 and vertical seismic coefficient (a ) = l/2cth i.e. 0 075. These coefficients are adopted for dynamic analysis of slope v stability. As regards using of seismic co-efficient value of zone IV of seismic zoning map of Ethiopia, it may be mentioned that for some other similar projects, almost same seismic co-efficient value has been adopted In the light of the fact stated above, it appears to be quite justified to use seismic co efficient value as per zone IV of seismic map of Ethiopia Annex A : Dam Final Detail Design Report/ 2009 3Erer Dam & Irrigation Project ZCECE & CES 4.0 Diversion Arrangements 4.1 General The design for a dam that is to be constructed across a river must consider diversion of stream flows around or through the dam site during construction period. Selection of the most appropriate scheme for handling the flow of the stream during construction is important to secure economy in the cost of the dam. The design flood for river diversion arrangement during construction is influenced mostly by the risk and damage factors involved in the diversion arrangements In the case of an earth fill dam the risk of over topping of embankment during construction may result in serious damage to works partially completed. This consideration may not be so for a concrete dam where flood water may overtop the partially constructed dam with little adverse effect Thus a proper diversion plan is to be evolved that will minimize serious flood damages to the work in progress at a minimum expense 4.2 Design Data Design data like flood peaks for flood of different return periods has been taken from the draft report on studies carried out by the Hydrology Group. The levels of river bed at dam site are based on longitudinal profiles parallel to dam axis 4.3 Design Flood for Diversion For large earth fill dams, river diversion design flood of 100-year return period is considered desirable as per BIS 14815: 2000 code. However in case of Erer dam, the valley at the proposed.dam site is very wide and flat. The maximum height of the dam is 36.6 m. Therefore, the river diversion works for construction of Erer Dam are planned to be designed for a flood of 50 years return period or to maximum observed flood at Erer site whichever is higher. The estimated peak floods for various return periods, based on GEV model are reported to be as below. Annex A : Dam Final Detail Design Report/ 2009 4Erer Dam & Irrigation Project ZCECE & CES Table 4.3: Estimated Flood Flows Return Period (year) Estimate Flood Peak (m /s) 3 5 58 10 82 20 120 50 151 100 179 The observed flood at the Erer dam site is not available and in the absence of which the computed flood for 50 year return period has been adopted for design of diversion works 4.4 Diversion Channel Design As already indicated earlier, the dam site is located in a wide valley with the foundation comprising of deep overburden both in the river bed and the banks. The diversion of flood by constructing a tunnel and coffer dams is to be thus ruled out. It is planned to diven flood flows through the body of the dam by constructing a temporary diversion channel during construction period The deepest riverbed at Erer dam site is reported to be at El 1348m Accordingly, it is planned to set the bed level of temporary diversion channel at the same elevation. A trapezoidal section of the channel is considered with the following parameters: • Design Flood 151 m3/sec • Bed width 30tn • Depth of flow 1.5 m • Side slope 1.5H:1V • Bed slope 1:164 Annex A . Dam Final Detail Design Report/ 2009 5Ercr Dam & Irrigation Project ZCECE <&: CES • Free Board 0.5m Area = 1.5 x (30+2x2 25)/2 = 48 75 m2 P= 30+2x 1.5^(1.5)2+(1)2 = 35.4 m A 48.75 R " P 35.4 R% = (1.3777)^ = 1.24 m 2 IZ2 Discharge Q =AXV =AX l/nXR * XS = 48.75X (1/0 03) X1.24X (1/164)1/2 =157.25 m3/s> 151 m3/s Hence the assumed diversion channel section is ok. 4.5 Methodology and sequence of diversion of river flow: Construction of concrete chute spillway of crest level 1379 m should be started in the first season and completed in one season. It is planned to divert the diversion design flood through a temporary channel involving a gap of about 30m through the body of the dam in the deepest river channel while the remainder of the embankment is being constructed. The side slope of the embankment across the opening shall be not be steeper than 4:1 to facilitate filling of the gap at the end of construction period and to decrease the danger of cracking of the embankment due to differential settlement. The flat slope also provides a good bonding surface between previously constructed embankment and the material to be placed for closure of the gap So far as the methodology and sequence of diverting the river water is concerned, this is to state that before the stream is diverted, the foundation treatment i.e. refilling of cut-off trench, construction of diaphragm wall and grouting as will be required should be completed in the area where the temporary opening will be left through the embankment. Embankment section on either side of the diversion channel forming part of fill placement Annex A : Dam Final Detail Design Report/ 2009 6Erer Dam & Irrigation Project /CECE & CES_______________________________________________ of dam with flatter slope 4:1 should be formed duly compacted in layers as per requirement of optimum moisture density of the material. The river flow may then be channelised through this area The foundation treatment followed by embankment placement in laryers on either side of the channel should proceed simultaneously to achieve the completion of dam embankment to top. During embankment placement, river water continues to flow through the diversion channel till sufficient progress is made in completion of embankment. Closure of the gap in the embankment can be made thereafter by making a dyke/ bund to facilitate working area dry during lean season flow. The average rale of embankment placement must be such that gap can be filled faster than the water rises in the reservoir and the work requires to be competed in one lean season i e. middle of October to middle of March. It is seen that to fill the gap up to the crest level of dam, the quantitites of earth filling required is about 420000m3. Even for a reasonably efficient contractor to achieve the progress of 375 m3/h target is not difficult. At this rate the total time requirement is about 1120hrs. Working for two shifts (8hrs/ shift) a day, it can be completed in only 70 days. However care must be exercised during filling of the gap so that quality of work is not sacrificed due to exigency of the situation. This is of great importance because the diversion gap is in the area where the dam height is maximum. Extreme care must be taken to obtain required densities so as to avoid excessive settlement of the embankment. Proper attention to bonding of new and old earth fill shall be specially attended. Drawing (Figure 4.1) showing the layout and cross section of diversion channel is presented 4.6 Closure of Gap The portion of the embankment to either side of diversion channel shall be taken - up for construction. The side slope of the embankment across the opening shall be not be steeper than 1H to 3V to facilitate filling of the gap at the end of construction period and to decrease the danger of cracking of the embankment due to differential settlement. The flat slope also provides a good bonding surface between previously constructed embankment and the material to be placed for closure of the gap. Annex A . Dam Final Detail Design Report/ 2009 7E196600 30 CM THICK PITCHING CHANNEL SECTION NOTES- 1 SIDE Slope and bed slope required to pass the DIVERSION FLOOD ARE 1 SH IV AND 1 154 RESPECTIVELY 2-SIDE SIOPE OF THE EMBANKMENT ACCROSS THE OPENING SHALL SOT BE STEEPER THAN4H IV FEDERAL DEMOCRATIC REPUBLIC OF ETHIOPIA MINISTRY OF WATER RESOURCES NCERT ENGINEERING ANS CONSULTING TRTFRPRKr IN ASSOCIATION WITH CONSULTING ENGINEERING SERVICt ( INDIA ) PVT. LTD ERER IRRIGATION PROJECT DETAIL DESIGN B AErer Dam & Irrigation Project /CECE & CES___________________________________________________ The diversion is carried through the opening in dam until sufficient progress is made in » « completion of embankment and appurtenant works so that flood can be carried safety through the completed or partially completed spillway. Closure of the gap in the embankment then can be made The closure of the gap shall be started by middle of October and completed by end of February to Middle of March. The average rate of embankment placement must be such that the gap can be filled faster than the water rises in the reservoir. Care must be exercised during filling of the gap so that quality of work is not sacrificed due to exigency of the situation This is of great importance because the diversion gap is in the area where dam height is maximum. Extreme care must be taken to obtain required densities so as to avoid excessive settlement of complete embankment Proper attention to bonding of new and old earth fill shall be specially attended. Annex A : Dam Final Detail Design Report/ 2009 8Erer Dam & Irrigation Project ZCECE & CES 5.0 Dam Height & Reservoir Levels 5.1 General The height of the dam is based on functional requirement of adequate storage in conjunction with operational and demand parameters set by downstream demands. The topographical features of the valley may also limit the height of a dam Siltation in the reservoir over period of time, seepage losses through reservoir and evaporation losses are to be accounted for in fixing the height of the dam. 5.2 Dead Storage Level The sediment inflow into the reservoir occupies the considerable part of reservoir storage. Studies have been carried out for sediment volume accumulated in the reservoir considering average annual silt rate According to the feasibility lavel study (WWDSE/ SHNERICS) the dead storage level (DSL) of 1369 85 has been fixed based on the sedimentation studies for New Zero Elevation after 50 years of reservoir sedimentation (see figure 5.1). 5.3 Minimum Draw Down Level (Mddl) After knowing the dead storage level and fixing the invert level of Irrigation Outlet (10), the MDDL is fixed in such a way that the depth of water above the centre line of 10 is at least equal to the height of opening. This will avoid the formation of vortex Accordingly MDDL has been fixed at EL. 1371. 5.4 Full Reservoir Level Simulation studies have been carried out with known MDDL and assumed FRL and outflow from outlet, inflow into the reservoir, evaporation and seepage losses The studies have been done using 35 years data and checking the success rate. The FRL has thus been fixed at EL 1379. Annex A : Dam Final Detail Design Report/ 2009 9Erer Dam & Irrigation Project ZCECE & CES Erer Irrigation Project Elevation Area Capacity’ Curves for 25 years of Sedimentation (FRL=1379 m) ____________ Area (Ha) « -Revised Area Original Area Revised Capacity —Original Capacity 5.4.1 Simulation for Fixing of FRL keeping demands constant In this case, FRL was varied from 1378m to 1386m keeping irrigation area as 4000 ha and d/s release as 0.1 cumec along with demands for domestic and livestock water supply indicated above. Results of simulation runs are indicated below in Table 5.1 5. 1: Erer Irrigation Project- Monthly Simulation Results No. of Periodwise failures (excluding first year) s. No. FRL (m) MDDL (tn) Area (ha) D/S release (MCM) Total no. of Periods Failure permissible As per simulation Irr (75%) WS (95% Irr Critical WS 1 1378.0 1371.0 4000 0.263 456 114 22 64 50 23 2 1379.0 1371.0 4000 0.263 456 114 22 52 37 20 3 1381.0 1371.0 4000 0.263 456 114 22 33 30 17 4 1382.0 1371.0 4000 0.263 456 114 22 31 30 13 Annex A Dam Final Detail Design Report/ 2009 10Erer Dam & Irrigation Project ZCECE & CES 5 1383.0 1371.0 4000 0.263 456 114 22 28 25 10 6 1384.0 1371.0 4000 0.263 456 114 22 26 24 9 7 1385.0 1371.0 4000 0.263 456 114 22 23 21 8 8 1386.0 1371.0 4000 0.263 456 114 22 22 18 7 Note: • For irrigation, supply in deficit years has been curtailed to 90% so as to supply water to more no of periods. • In case irrigation deficit is more than 25% of the demand, then that period/year has been categorized as critical failure • WS includes all demands except irrigation. Failure for WS means failure for irrigation also • Performance for irrigation and WS are judged for 75% and 95% success respectively. • Revised Elevation-Area-Capacity values for 25 years of sedimentation have been considered. Dead storage level is as per 50 years of sedimentation. • Upper, middle and lower rule levels are same as Full Reservoir Level (FRL), Minimum Draw Down level (MDDL) and MDDL respectively. From the above table, it is seen that for FRL value of 1379.0 m no of failures are within the desired limit of 22, therefore FRL of 1379.0 m has been finally adopted to meet the irrigation water requirement for 4000 ha, d/s release of 0.1 cumec (0.263 MCM) and demands for domestic and livestock water supply. 5.4.2 Simulation for Increased Downstream Release with Area Varying In this simulation FRL was kept as 1379.0 m, as finalized above, d/s release was increased from 0.1 cumec (0.263 MCM) to as 0.5 cumec (1.315 MCM) and irrigation area was varied till failures are within the desired limit. Upper rule level was kept equal to FRL (1379.0m), and middle and lower rule levels were kept equal to MDDL (1371.0m). Results of simulations for are given below in Table 5.2 Annex A : Dam Final Detail Design Report/ 2009 11Erer Dam & Irrigation Project /CECE & CES Table 5. 2: Erer Irrigation Project- Monthly Simulation Results (FRL=1379.0m, D/S Release=0.5 cumec or 1.315 MCM, Area =Varying) No. of Periodwise failures (excluding first year) s. No. FRL (m) MDDL (m) Middl e Rule Curve Area (ha) D/S Release (MCM) Total no. of Periods Failure permissible As per simulation Irr (75%) WS (95% Irr Criti cal WS 1 1379.0 1371.0 1371.0 4000 1.315 456 114 22 113 93 41 2 1379.0 1371.0 1371.0 3800 1.315 456 114 22 109 86 40 3 1379 0 1371.0 1371.0 3600 1.315 456 114 22 86 70 34 4 5 1379.0 1371.0 1371.0 3400 1.315 456 114 22 64 47 27 1379.0 1371.0 1371.0 3200 1.315 456 114 22 37 30 15 Note: Upper and lower rule levels arc same as Full Reservoir Level (FRL) and Minimum Draw Down level (MDDL) respectively It is seen from the above table that when d/s release is increased from 0.1 cumec to 0.5 cumec, irrigation area will have to be reduced from 4000 ha to 3200 ha to keep the WS failure within permissible limits with adopted FRL of 1379.0 m. 5.4.3. Conclusions From the simulation results given above for different alternatives, following conclusions can be drawn: • FRL of 1379.0m is sufficient to meet the full estimated annual demand of 50 11 MCM to keep the failures for WS and irrigation within desired limit. • With adopted FRL of 1379.0m, irrigation demands for only 3200 ha can be met with increased d/s release from 0 1 cumec to 0 5 cumec Annex A Dam Final Detail Design Report/ 2009 12Ercr Dam & Irrigation Project /CECE & CES • ' For d/s release of 0.5 cumec and area of 4000 ha, even FRL of 1386.0m is not enough to keep the number of failures within desired limit. This is due to the fact that numbers of consecutive years are dry to very dry years. • Based on above simulation studies, FRL of 1379.0 m has been adopted to meet estimated planned water requirement of 50.11 MCM for planning, design and other studies 5.5 Maximum Reservoir Level The design inflow flood of as recommended by hydrology group has been adopted for flood routing considering different length of spillway. Finally 30m length of spillway has been considered 5.5.1 Elevation-Storage-Outflow Data Elevation storage data for Erer reservoir for FRL as 1379 0m for 25 years of sedimentation given in Table 3.14 has been used. Outflow from spillway has been worked out using the following equation: Q=C LH d l3 where, Q (cumec) is the outflow discharge, Cd is the coefficient of discharge (1.18), L (m) is the length of spillway (m) and H (m) is the depth of flow above the spillway crest level of 1379.0 m. Outflow from spillway has been worked out considering L as 30m, 40 m and 50 m. 5.5.2 Inflow Hydrograph Design flood hydrograph (figure 5.1) as given below with a peak value of 642 cumec at 20 hours has been adopted for routing. Annex A : Dam Final Detail Design Report/ 2009 13Erer Dam & Irrigation Project ZCECE & CES____________________________________ Initial reservoir level for reservoir routing has been considered as FRL (1379.0m). Figure 5.1: Design Flood Hydrograph 5.5.3 Results of Reservoir Routing Reservoir routing was carried out using above data as input. Summary of results of routing are given in Table 5.3 Table 5.3: Summary of Reservoir Routing Results by Modified Puls Method Peak Inflow Peak outflow Case no. L (m) Time (hrs.) Ordinate (cumec) Time (hrs.) Ordinate (cumec) Max. Reservoir level (m) 1 30 20 641.9 26 440.5 1382.55 II 40 20 641.9 25 491.72 1382 16 III 50 20 641.9 25 526.3 1381.85 It is seen from the above Table 5.3 that maximum reservoir level attained after reservoir routing varies from 1381.85m for spillway length of 50m to 1382.55m for spillway length of 30m. Based on the above results, maximum reservoir water level (MWL) and other Annex A : Dam Final Detail Design Report/ 2009 14Ercr Dam & Irrigation Project /CECE & CES____________________________________________________ physical, technical and economical factors, spillway length of 30m with MWL of * < 1382.55m has been adopted for further planning and design. Fig. 5.2 shows plot of inflow, outflow and reservoir elevation for reservoir routing for spillway length as 30 m. Figure 5.2: Reservoir routing (L=30m) Erer Irrigation Project-Reservoir Routing (L=30 m) 1383.0 1382.5 1382.0 1381 5 1381.0 1380.5 1380.0 1379.5 1379.0 1378 5 Time (hrs.) -—-Inflow ——Outflow Elevation 5.6 Top of Dam Embankment (Dam Crest Level) 3 To arrive at Top of Bund level, free board above FRL and above MWL are worked out. The free board above FRL is known as normal free board and that above MWL is known as minimum free board. T Seville's method has been used for working out free board 5.7 Free Board 5.7.1 General Adequate freeboard over FRL and MWL is required to be provided to guard against the overtopping of dam embankment under design wave conditions. For this, the requirement of normal free board at FRL and minimum free board above MWL are calculated. The free Annex A : Dam Final Detail Design Report/ 2009 15Ercr Dam & Irrigation Project /CECE & CES__________________________________________ board that gives the highest requirement of TBL (Top Bund Level) needs to be finally * < adopted. Indian standard IS 10635 “Guidelines for Freeboard Requirement in Embankment Dams” requires that the normal free board at FRL be calculated by adopting the full wind velocity and by considering design wave height (Ho) as 1 67 times the significant wave height (Hs), subject to the condition that normal free board should not be less than 2.0 m In calculating the minimum free board at MWL, wind velocity is taken as half to two third of full wind velocity while the design wave height (H ) is taken as 1.27 times the significant o wave height (Hs). The minimum free board is subjected to a minimum of 1.5 m. 5.7.2 Calculation of Normal Free board: Significant wave height is a function of wind velocity and effective fetch. Effective fetch (Fe) of a reservoir is given by the following relation: Fe = Zx;«Cos6*Cos0 / ECosO Where X, = the length of any radial at an angle 0 from the central radial. The values of X, arc read from the map of Erer reservoir after plotting radials at an interval of 6 degrees up to 42 degrees on both sides of central radial. Table 5.4.2 Computation of Effective Fetch For FRL 0 Cos 0 X, Xi Cos 8 Cos 8 42°”” .743 1147.02 633.211 36° .809 4839.701 3167.492 30° .866 3853.77 2890.157 24° .914 2816.53 2352.917 18° .951 2311.344 2090.381 12° .978 2073.285 1983.063 6° .995 1875.826 I 1839.294 0° 1.00 1901.514 1901.5141 6° .995 1412.733 1398.641 7? .978 1473.26 1409.149 ’18° .951 1550.607 1402.371 24° .914 1078.272 900.784 Annex A : Dam Final Detail Design Report? 2009Erer Dam & /CECE & CES 30° .866 1140.666 855.449 ’36° .809 1117.68 731.50 42° .743 905.925 500.115 I = 13.512 21289.66 24056.07 = 24056.07/13.502 = 1.78km Data on basic hourly wind speed in Erer region is inadequate to arrive at 50year return period wind velocity. USBR recommends for using wind velocity of the order of 120Km/hr to 160 Km/hr. Accordingly the basic wind speed on land for 50 years return period (U) has been considered as 143.7 km/hour or 33.33 m/sec. Wind velocity on water surface (V) is obtained by multiplying wind velocity on land (U) by co-efficient Q for given effective fetch. As per IS: 10635, the coefficient Q for an effective fetch of 1.78 km equals to 1.15 Hence, design wind velocity on water surface (V) shall be 42.3 m/sec or 160.94 km/hr. Significant wave height (Hs) is calculated using relationship given in graphical diagram with related factors i.e. for a given wind velocity and effective fetch For v = 38.33 m/s and fe = 1.78km Hs = 1 2 m Wave period (Ts) is also computed using relationships given in graphical diagram With related factors i.e. wind velocity and effective fetch So Ts = 3.4/ Seconds Wave Length (Ls) is computed by the relationship: Ls = 1.56 Ts2 = 1.56 x 3.42 = 18 03m Design wave height (Ho): Ho = 1.67 Hs = 1 67 x 1.2 = 2.004m Annex A : Dam Final Detail Design Report/ 2009 17Ercr Dam & Irrigation Project /CECE & CES______________________________________________ Steepness ratio, Ho/Ls = 011 Embankment slope = 1 in 3 i.e. 0.33 For embankment slope of 0.29 and Ho/Ls = 0.11, R/Ho = 1.3 Where R denotes wave run up on smooth surface Hence R = 1.3 x 2.004 = 2.605m The wave run up on rough surface (Ra) is computed by multiplying surface roughness coefficient to wave run up on smooth surface Value of surface roughness co-efficient for dumped riprap = 0.50 Hence Ra =0.5x2.605 = 1.303m IS Code provides that if the wave run up on rough surface (Ra) is less than designed wave height (Ho), Ra shall be taken as Ho Hence Ra = 2..004m Average water depth (D) in the reservoir has been considered as 31 m. Wind set up (S) is calculated by the formula S = V . F/ (62000 x D/2) Where, F = maximum Fetch in km = 1.9Km V = wind velocity in km/h = 138 = 138 x 1 9/(62000 x 27/2) = 0 12m Normal Free board required above FRL = Ra + S = 2.004 + 0.12 = 2 12 m The effective fetch length is calculated as presented below in table 5.5 2 2 Annex A : Dam Final Detail Design Report/ 2009 18Ercr Dam & Irrigation Project ZCECE & CES______________________________________________ '• Table 5.5.3: Computation Of Effective Fetch For MWL 9 Cos 9 Xi Xi Cos 9 Cos 9 42° .743 2257.08 1105.969 ^36°“ .809 5338.795 2978.019 3o°' .866 3970.925 3317..295 24° .914 2867.568 2338 332 18° .951 2585.504 2395.555 12° .978 2238.329 2140.926 .995 1972.056 1952.384 0° 1.00 1979.128 1979.128 6° .995 1979.128 1949.516 12°~ .978 1502.94 1437..54 18° .951 1613.86 1534.788 24° ” .914 1248.5 1042.992 30° .866 1220.559 936.329 36° .809 1179.176 771.748 42° .733 1116.366 599.811 2 = 13.512 I =26477.648 Fe = Sxi cos O.cos 9/ E cos 9 Fe=_26477.648 / 13.512 = 1.96 km Calculations for minimum free board at maximum water level (MWL) are presented in Table-5.6. MWL Fetch Length (FRL, MWL) - - 1382.6 m for 1/2PMF 1.96 km Slope of Embankment - 1 V in 3.0 H up to berm and thereafter 1 in3 5 Table : Computation of Free Board SI No Computed Item Calculation for Normal Free board Calculation for Minimum board 1 Effective fetch (Fe) in km 1.78 1.96 2 Wind velocity over land (U) in km/h 120 80 3 Wind coefficient (Q) 1.15 1.15 4 elocity over water surface (V) in km/h 138 92 5 Significant wave height (Hs) in m 1.2 0.85 6 Wave period (Ts) in seconds 3.4 3.0 7 Wave length (Ls) in m 18.03 14.04 8 Design wave height (Ho) (m) 2.004 1.419 9 Wave steepness Ho/Ls 0.11 0 101 Annex A : Dam Final Detail Design Report/ 2009Ercr Dam & & 10 Relative Run-up R/Ho 1.303 1.25 11 Run-up (R) in m 2.605 1.845 12 Run-up(Ra) considering on dumped rip rap in m 1.303 0.922 13 If Ra < Ho, design Ra=Ho 2.004 1.419 14 Average depth of reservoir (D) in m 31 33.6 15 Wind set-up in m 0.12 0.008 16 Free board required 2.12 1.426 17 Permissible freeboard (m) 2..0 1.5 5.7.3 Settlement due to strong Ground Motion In fixing the freeboard for an earth or rock fill dam, allowance also needs to be made to the settlement of embankment under the shaking action of earthquake vibrations/seiches Hence allowance has been provided for these aspects in fixing the free board An allowance of 0.5m is considered in computing the free board for settlement due to earthquake-induced shock Total freeboard required above FRL= 2.12 + 0.5 = 2.62 m Total freeboard required above MWL= 1.5 + 0.5 = 2. m 5.7.4 Dam Crest Level or Top Bund Level (TBL): TBL on consideration of normal freeboard above FRL=1379 + 2.62= 1381.62 m TBL on consideration of minimum freeboard above MWL = 1382.6 + 2. = 1384.6m It is seen that the criteria of minimum freeboard above MWL is the governing condition for fixing the TBL and that the TBL is required to be at or above EL 1384.6 m. In the selected scheme, the dam crest is at El 1384.6 m A 1.0 m high parapet wall shall be constructed above dam crest a|ong the upstream face of the dam 5.8 Height of the Dam The general river bed level at dam site is 1348m. Thus, the height of Erer Dam, as per selected scheme would be about 36.6m above riverbed level. Annex A : Dam Final Detail Design Report/ 2009 20I R Erer Dam & Irrigation Project ZCECE & CES * 5.9 Significant Levels I I r i i i i i I Significant data of Erer dam and reservoir are provided below,in table 5.7 Table 5.7.5 significant data of dam Dam Top of parapet guard wall El. 1385.6 Embankment crest El. 1384.6 General Riverbed El. 1348.0 Height above riverbed 36.6 m Reservoir Maximum waler level El. 1382.6 Full Reservoir level El. 1379.0 Minimum Drawdown Level El 1371.0 Gross storage 5067.5 ham Live storage 2303.4 ha m | 6.0 Various components of Embankment dam 6.1 Crest Width _ Largely precedent, keeping in view the possible roadway requirements, has determined the crest width of Erer dam. Following considerations have guided the selection of crest - width: £ • The Indian standard: 8826, ‘Guidelines for Design of Large Earth and Rock fill Dams’ lays down that the crest width should be fixed according to the working I space required at the top and that the crest width should not be less than 6m. • Design of small Dams by USBR suggests following formula for determining crest (width for small earth fill dams: Annex A : Dam Final Detail Design Report/ 2009 21 I C".Erer Dam & Irrigation Project /CECE & CES w = z/5+ 10 Where w = width of crest in feet and z = height of dam in feet above the riverbed. The height of Erer Dam above river bed being 33.5m (109.88 feet), width of dam crest = 32 feet or 9.75m • ‘Design of Large Dams’ by Thomas refers to Japanese Code 1957 that specifies crest width W in terms of height of dam (H) as: W = 3.6 x V77" - 3(meler ) For Erer Dam, W = 3 6 x 3/-33.S-3 W=11.6-3 = 8.6 m Based on above, a crest width of 9 m has been selected for Erer dam. 6.2 Camber/ settlement allowance Appropriate camber shall be provided along the crest of dam to ensure that the free board is not diminished by foundation settlement or embankment consolidation. It is expected that the major portion of the embankment consolidation will take place during the construction and thus the camber along the axis of dam is required to take care of the expected foundation settlement IS 8826 stipulates that settlement allowance of 1 percent of the maximum height ofthe dam shall be provided for settlement of embankment dam on unyielding foundation. Accordingly, a longitudinal camber of 36.6 cm has been provided on dam crest along the axis of Erer dam. The camber varies from zero height at the abutments to 35.6cm at the central section in the valley. 6.3 Parapet wall A parapet wall of lm height on the upstream side of crest of dam is provided for an additional safety. This is over and above the required height of the designed f free board. Annex A : Dam Final Detail Design Report/ 2009 22Erer Dam & Irrigation Project ZCECE & CES 6.4 Guard stones Guard stones of size 300x 300x750mm have been provided in cement concrete blocks 1:3:6 at 3m c/c on the downstream edge of top of dam. 6.5 Berms Berms have been provided along upstream and downstream slopes for serving the following purpose: • For providing level surface for construction and maintenance of the dam section. • For reducing the surface erosion in case of downstream slope and breaking the continuity of the slope. • To protect the lower edge of the rip rap and for preventing it from undermining in case of the upstream slope Five meter wide berms have been provided at vertical elevation of 1369m both on upstream and downstream slopes. A 6.0 m wide berm at top elevation of rock toe has also been provided on the downstream slope of dam. To prevent rain water from flowing over the outer edge of berm, the surface of berm is given a cross slope of 1 50 towards the inner edge. A gutter is provided at the inner edge to cany rainwater to one side of valley where a vertical gutter is provided to lead the water to river channel downstream 6.6 Impervious Core A centrally located core has been selected for Erer Dam as it has the advantage of providing higher pressure at the contact between the core and the foundation, thus, reducing the possibility of leakage and piping The top level of the core is generally fixed at 0.5 to 1 meter above MWL to prevent seepage by capillary siphoning. In case of Erer dam, the MWL being 1382.6m, the top level of the core is fixed at EL 1383 60m Annex A : Dam Final Detail Design Report/ 2009 23Ercr Dam & Irrigation Project ZCECE & CES______________________________________________ The minimum top width of the core as specified by Indian standards is 3 m. Since availability of suitable impervious material is not a constraint, a width of 5m has been adopted at top of the core with upstream and downstream slopes of 1H 1V. The impervious soils to be placed in impervious core should not be highly compressible and the liquid limit should not be very high as such soils are prone to swelling and formation of cracks. Soils having organic content are also not suitable. Borrow area investigations carried out for sourcing different construction materials have identified the clayey sand, sandy clays of medium plasticity which are suitable for impervious core. 6.7 Shell Zones It is proposed to use sandy gravel material in shell zones upstream and downstream of clay core. It is desirable that material should be well graded so that it may be compacted to high dry unit weight of the order of 19.0 kN/m3. The compacted soil in this zone should have an average relative density of 75% but the soil compacted to RD less than 70% in any layer shall not be acceptable as the soil with RD lower than 70% stands a high risk of liquefaction during a strong earthquake The material in upstream shell zone, above the minimum draw down level, is required to be fairly free draining (k > 5 x 10 3) so as to allow rapid dissipation of pore water pressures. This requirement arises to ensure stability under seismic loading. It is, therefore, being provided in the scheme of zoning that the material on upstream shell above MDDL (zone 2) should not have silt content more than 6%. For the material in upstream shell below MDDL and downstream shell, the limitation of silt to 6% shall not be binding. The field investigations of borrow areas indicate that it should be possible to get sandy gravel material with silt less than 6% by selective borrowing. In fact, the gradation tests on the two samples of sandy gravel soil collected from the selected borrow areas show very low percentage of silt fraction. The material in upstream shell zone, above the minimum draw down level, is required to be fairly free draining” (k > 5 x 10 "3) so as to allow rapid dissipation of pore water pressures. This requirement arises to ensure stability under seismic loading It is, therefore, being provided in the scheme of zoning that the material on upstream shell Annex A : Dam Final Detail Design Report/ 2009 24Ercr Dam & Irrigation Project ZCECE & CES______________________________________________ above MDDL (zone 2) should not have silt content more than 6%. For the material in upstream shell below MDDL, the limitation of silt may go upto 10% to 12%. 6.8 Cutoff In the abutments the fresh rock is met with at a depth of 7m or so Due to presence of rock at relatively shallow depth, it is proposed to construct a positive cutoff trench in the abutments from RD. 0.0m to RD 468.0m and from RD. 895.0m to RD. 1482m. As discussed in the foundation treatment chapter , in the river bed portion I,e from RD 468.0m to RD. 1482m where the overburden is about 18m to 19m, a cutoff trench of 4m deep and 6m wide at its base is suggested to facilitate the construction of plastic concrete diaphragm wall and to keep the top of diaphragm wall within the trench as already explained 6.9 Rock Toe The principal function of rock toe is to facilitate drainage of seepage water Besides providing drainage, a rock toe improves the stability of the downstream slope. It also protects the lower part of the downstream slope from tail water erosion. Indian standard recommends the height of rock toe to be about 20 percent of hydraulic head at that section with maximum and minimum limits of 6m and lm respectively. Accordingly the rock toe of height H/5 (6m) above the deepest riverbed level of 1348 has been provided to protect it against tail water erosion. A 6m wide berm has been provided at the top level of rock toe (El 1354). The rock toe consists of stones of size usually varying from 150mm to 200mm with maximum stone size of 0.5m3 A filter is to be provided between the rock toe and the soil mass in the dam as well as in the foundation Accordingly 200mm thick sand layer overlain by 200mm thick gravel/ metal layer at the foundation level and between d/s shell has been provided 6.10 Toe Drain An open toe drain is provided at the downstream toe of the dam in continuation'of slope The bed width of toe drain is kept as 0.6-lm and depth as 0.6m. Thcsdcain is paved _______________________________ '__________________ ____________ /< ^ ' \ V Annex A : Dam Final Detail Design Report/ 2009 I svErer Dam & Irrigation Project /CECE & CES________________________________________ with stones with suitable gravel and sand layers of 0.2m thickness each so that sloughing of d/s slope is prevented. 6.11 Upstream Slope Protection Erer dam being an earth fill dam, its upstream slope needs to be protected against destructive wave action As described in the in the design criteria the Dumped rock riprap is most effective and durable Accordingly, it is proposed to provide dumped rock riprap for upstream slope protection of Erer Dam It is required that the rock for riprap should be hard, dense, and durable, and should be able to resist long exposure to weathering In case of Erer dam, stone/rock fragment of good quality granite gneisses rock are available close to dam site The individual pieces of dumped riprap need to be of sufficient weight to resist displacement by wave action USBR recommends that the maximum size of stones, for a reservoir fetch 2.5km or less should be around 1150 kg. The thickness of the riprap needs to be sufficient so as to accommodate the weight and size of stone necessary to resist wave action. USBR recommends a 1.0 m thickness of dumped riprap for major dams. The design criteria recommended by Taylor relates the selection of rock size and thickness of the riprap layer directly to the design wave height. Recommended riprap thickness for different ranges of wave height are as per Table 6 1 Table 6.1 Recommended Riprap Design Criteria Maximum wave Height (m) Average rock size D (cm) Maximum rock Size (kg) Layer thickness (cm) 60 0-0.31 20 45 31 0.31-0.61 25 91 38 0.61-1.22 31 227 46 1.22-1.83 38 680 61 1,83-2.44 46 1134 76 2.44-3.05 61 1814 91 Annex A : Dam Final Detail Design Report/ 2009 26Erer Dam & Irrigation Project /CECE & CES 3 The criteria of minimum average rock size imply that the riprap should be composed of rocks, half of which are larger than the recommended D30 size for given wave height The rock should be well-graded, from a maximum size of above 1.5 times the average size varying down 2.5 cm spalls to fill voids between rocks and to provide a reasonable degree of protection to the underlying filter layer. The normal size of rock (D) is determined assuming the rock fragments to have a volume between that of a sphere and a cube, or %. D = w/y Where, y = Unit weight of stone in kg/m and w - weight of stone in kg Considering y = 2lOOkg/m3 D = 0.08w1/3 Based on the considerations narrated above, the thickness and gradation of dumped rock riprap for Erer dam, proposed to be adopted are as below: 3 • Thickness of dumped rip rap 1.0 m • Maximum size of stones 2000 kg or 1000 mm • 40 to 50 percent grater than 1000 kg or 800 mm • 50 to 60% 45 kg- 1000 kgor 300 to 800mm • Oto 10% less than 45 kg or 300 mm • Sand and rock dust shall be less than 5 % by weight, of the total rip rap material The shape of the rock used for dumped riprap influences the ability of the riprap to resist displacement by wave action At Erer dam, the riprap will mostly comprise of angplar Annex A : Dam Final Detail Design Report/ 2009 27Erer Dam & Irrigation Project ZCECE & CES______________________________________________ fragments of quarried granite rock, which provide better resistance to displacement under wave action. It is required that the riprap should extend from the crest of dam to about 2.0 meter below the minimum draw down level to take care of the wave run - down with the reservoir at MDDL. Accordingly, the riprap for protection of upstream slope has been provided upto EL 1369m from dam crest. Since the shell material in Erer dam will be sandy gravel, it is necessary to provide a blanket of graded gravel underneath the riprap. Such a blanket is necessary for Erer dam to guard against the danger of fines getting washed out through the voids in the riprap by wave action. The design requirement for the filter blanket is that 15 percent of filter material should be coarser than 50 mm for a graded riprap. Accordingly, a 50 cm thick blanket of crushed rock or natural gravel graded from 4.75 mm to 80 mm is being provided below the dumped rock rip on upstream slope. 6.12 Down Stream Slope Protection Downstream shell zone of Erer Dam being composed of sandy gravel material, the downstream slope needs to be protected against erosion by wind and rainfall runoff. Such protection of downstream slope is generally provided either by vegetative cover or by a layer of rock or cobbles. Erer dam being located in semi-arid region, reliance can not be put on protection of downstream slope by grass turfing. Hence, the downstream slope is proposed to be protected by a 30cm thick stone pitching. Annex A : Dam Final Detail Design Report/ 2009 28Erer Dam & Irrigation Project ZCECE & CES 7.0 Stability Analysis of dam 7.1 General The basic approach in design of dam embankment has been to select a dam section based on the precedence of outer slopes in dams adopted for constructed dams The selected section is then analyzed by the approach specified in IS: 7894 “Code of practice for Stability Analysis of Earth Dams”. The factors of safety computed for critical combination of external forces are compared with the minimum factor of safety stipulated in the code. The outer slopes of the embankment are optimized such that the computed factors of safety are higher than, but close to, the minimum desired values under various loading conditions Thus, the pre-requisites for stability analysis are selection of test dam section and the engineering characteristics of materials to be used in various zones. 7.2 Material Properties Considered for Analysis 7.2.1 Material in Impervious Core As described under paragraph 7.1 above, the material in impervious core shall be clayey sand/sandy clay. Samples of such soils collected from identified borrow areas have been tested at WWDSE laboratory. The test results are indicated in the Table 7.1: Table 7.1: Properties of Clay Borrow Areas: CLAY BORROW AREAS Laboratory Tests EB-1 EB-2 EIP-11/06 EIP- 12/06 EIP- 13/06 EIP-14-16/06 Grain size analysis Clay •/. 5.00-35.00 17.00-29.90 16.50 27 00 25.00 9.00-41.00 Silt •/. 13.63-71.29 16.41-24.30 27.44 40.36 32.20 7.5-41.48 Sand % 7.71-81.37 40.10-63.59 56.06 32.64 42.80 17.52-83.5 Atterbere limit LL 24.27-50.80 33.00-48.90 39.37 47.69 49.67 24.26-46.35 PL 13.37-2626 14.19-24 29 16.19 26.59 26.27 12.63-23.77 PI 15.29-28.79 14.28-29.18 23.18 21.10 23.40 11.63-22.58 Procter test MDD (Km/cc) 1.567-1.89 1.76S-1.823 i ■ OMC % 12.20-23.70 14.S0-16.80 Shrinkage 1.00-14.00 11.00-16.00 9.79 14.20 14.98 4.91-14 95 Annex A : Dam Final Detail Design Report/ 2009 29Erer Dam & Irrigation Project ZCECE & CES limit Free swell 35-75 40.00-60.00 13.50 14.00 13.00 11.00-14.90 Specific gravity 2.52-2.70 2.61-2.65 Consolidation 0.083-0.134 Direct shear C (Kpa) 43.67-92.67 48.67-83.30 *(□) 20.56-34.22 27.47-28.81 Permeability (cm/scc) 0.749- 3.97*10’7 Triaxial test (UU) C (Kpa) 16.01-26.67 14.79-32.42 0>(Q) 6.00-16.00 7.00-13.00 7.2.2 Material in Shell zones The important engineering properties relevant to the stability of dam slope are specific gravity, dry density of compacted soil, permeability and effective shear parameters. Theses parameters are presented below (table 7.2) for the materials under consideration Table 7.2: Properties of Shell Material Tests Conducted ESHQ1 (%) ESHQ2 (%) Gravel (%) 58.91 -64.28 42.67-47.12 Sieve Analysis Sand(%) 32.62-39 3 50.16-54 24 fines (%) 1 75-3.25 2.72-3.01 Direct Shear Test Cohesion (kpa) N.A 9-23.33 (J)(degree) NA 37.05-37.25 Permeability K (cm/s) NA 0.16-2 35* IO'3 Since the sandy gravel soil placed in shell zone is cohesionless, it is very important that the material is compacted to fairly high relative density The soil in the shell zones is to be compacted to achieve an average relative density(RD) of 75%. For the purpose of stability analysis the compacted unit weight of the soil has been taken corresponding to 70% relative density. The values of dry unit weight in densest state C/dnux) and dry unit weight in loosest state (yumin) have been considered as 16.4 and 20.2 kN/m respectively. The corresponding value of dry weight for 70% relative density works 3 Annex A : Dam Final Detail Design Report/ 2009 30Erer Dam & Irrigation Project /CECE & CES______________________________________________ out to 18.9 kN/m3. The dry unit weight of 18 kN/m3 has been considered for the purpose of stability analysis. The value of shear parameters adopted for sandy gravel material in shell zones are guided by the laboratory tests on material in selected borrow areas which are yet awaited. The assumed value of <U’ is taken as 35° for stability analysis. Value of O’ for down stream shell zone material is assumed lower than the corresponding value for u/s shell zone 2 material Thus, for the purpose of stability analysis following two sets of values of O’ have been considered: Set Zone 2 Zone 2A 1 35° 32° 2 33° 30° The permeability of shell material is generally found to vary from 10 to J 10 cm/s. Accordingly the following of permeability have been assumed for stability analy sis 2 Zone 2 = 5x10“° cm/s Zone2A= 10'4 cm/s Based on above considerations, the material characteristics as per table 7.3 have been considered for stability analysis. Table 7.3: Material Characteristics Zone Sp. Gravity Unit Weight (kN/m ) 3 Permeability (cm/s) C’ (kpa) 0 Degree 1 Core 2.64 17 9 3.9 x 10! 20 29 2 Casing 2.64 18.5 5x103 0 35/32 2a Casing 2.64 18.5 2.5x10'* 0 33/30 4 Filter 2.64 18.0 10’2 0 28 Sfoundation 2.65 1.6 io-5 25 20 Annex A : Dam Final Detail Design Report/ 2009 31Ercr Dam & Irrigation Project /CECE & CES 7.3 Loading Conditions IS: 7894 states that stability of upstream & downstream slopes be checked for following conditions which are usually found to be critical for the stability of an earth dam Construction condition with or without partial pool (for U/s and D/s slopes) • Sudden drawn down (for U/S slope) • Steady seepage (for D/S slope) • Earthquake condition (for U/S and D/S slopes). 7.4 Minimum Factor of Safety Minimum desired values of factor of safety under various loading conditions, specified by Indian Standard are as per Table 7.4 Table 7.4: Minimum Desired Values Of Factors Of Safety For Various loading Conditions Case No. Loading condition Critical Slope Minimum Factor of Safety I Construction condition with or without partial pool U/S & D/S 1.0 II Sudden draw downs with tail water at maximum U/S 1.3 III Steady seepage of Dam with reservoir full D/S 1.3 IV Steady seepage with seismic loading D/S U/S 1.0 7.5 Stability Analysis Stability'analysis and analysis for seepage through the dam body was said to be carried out at the feasibility stage by using soft ware SLOPE/W and SEEP/W developed by Geoslope, Canada* The software uses the general limit equilibrium (GLE) formulation for estimating the factor of safety in stability of upstream and downstream slopes for various loading conditions. Annex A : Dam Final Detail Design Report/ 2009 32Erer Dam & Irrigation Project /CECE & CES The GLE formulation is based on two factors of safety equations and allows for a range of inter slice shear normal force assumptions. One equation gives the factor of safety with respect to moment equilibrium (Fm), while the other equation gives the factor of safety with respect to horizontal force equilibrium (Ff). The GLE method satisfies both moment and force equilibrium by finding the cross-over point of the F m and Ff. The software analyses large number of slip circles based on Bishop, Janbu, Morgenstem-Price & Spencer methods and exhibits the minimum factor of safety for the critical failure surface. Stability analysis of Erer dam for steady seepage state was carried out by considering head pond level at FRL and no water at tail of the dam The stability of downstream slope under steady state was checked with and without consideration of seismic loading The stability of upstream slope, under steady seepage state, was checked only with seismic force acting from right to left For the stability of upstream slope under sudden draw down condition the derived factor of safety is dependent upon the rate of reservoir draw down and the rate of dissipation of pore water pressures. In case of Erer Dam, the draw down was considered to be taking place from FRL to MDDL, by flow passing through irrigation outlet. The discharging capacity of irrigation outlet being limited, the draw down below spillway crest level of 1379m to MDDL of 1371 m will be slow The construction condition represents a situation when the dam is just constructed and the pore pressures developed as a result of dam material compression are only partly dissipated. The residual pore water pressures depend on the moisture content and the compaction efforts deployed during construction as well as on the rate of rise of the dam The residual pore water pressures under this condition are considered as based on the pore water.<pressure ratio R^, a coefficient that relates the pore water pressure to the overburden stress. The pore water pressure u is given by: u = Ru Yt H s s Where, yi = total unit weight H = the height of the soil column Annex A : Dam Final Detail Design Report/ 2009 33Erer Dam & Irrigation Project /CECE & CES______________________________________________ The value of the Ru considered in the analysis is 0.35. The stability analysis carried out on adopted section was found to be safe since the factor of safety values under all loading conditions were found to be within the permissible limit. The stability analysis of the dam section as adopted at feasibility stage is also carried out with the help of ‘SLIDE’, a software meant for slope stability analysis of soil and rock developed by Rocscience Inc, Canada The section is found to be safe. The section of the dam finally arrived at is enclosed vide Fig. 7.1 The stability analysis results as carried out by SLIDE are attached vide Annexure-1. Annex A : Dam Final Detail Design Report/ 20091 o o 1 CD J> 4 Axis of Dam 9C3O ▼ 1384.60 1348 0 3 : — 40(\) ------------- Acceptable foundation grade Silty Clay Graval plastic Concrete diaphragm wall 1) Impervious Soil - SC.CL, 2) Pervious to semipervious - SW, GP.GW.SP 2A) Semipervious - SM.GM Chimney filter Horizontal filter Rock Toe Dumped Rock Riprap Blanket of crushed rock or gravel below dumped Riprap Hand placed Riprap Key trench Toe drain NOTES 1) All dimensions are in millimeters and levels in metres unless otherwise specified. 2 2) For layout plan of dam refer relevant drawing 3) For detail of Crest,Riprap & Rock Toe refer relevant Drawing. FEDERAL DEMOCRATIC REPUBLIC OF ETHIOPIA MINISTRY OF WATER RESOURCES PROJECT: ERER IRRIGATION PROJECT DETAIL DESIGNErer Dam & Irrigation Project ZCECE & CES 8.0. Geology along dam axis Five boreholes have been drilled along dam axis. The exploration revealed overburden zone of about 19m below deepest river bed in the valley portion Out of this 18m, the top 7m comprises of silty clay and sand mixed with gravel underlain by coarse gravel and cobble mixed with sand resting on crystalline gneisic rock. In the abutments, the depth of overburden comprises of mainly silty clay, sand mixed with gravel and varies from 6m to 7m in general. The geological profile along dam axis based on sub-soil exploration result is shown vide Fig. 8.1 Annex A : Dani Final Detail Design Report/ 2009 35ELEVATION IN METER elevation in meter EAST LEFT BANK VEST RIGHT BANK 1390 ----------- 1385 _ 1380 1375 1370 1365 1360 1355 1350 1345 1340 1335 1330 1325 132Q. GROUNO LEVEL (M) CHAINAGE (M) SILTY CLAY, SAND. MIXED WITH GRAVEL FEDERAL DEMOCRATIC REPUBLIC OF ETHIOPIA MINISTRY OF WATER RESOURCES WEATHERED GRANITIC GNEISS COURSE GRAVEL. COBBLE MIXED WITH SAND FRESH GRANITIC GNEISS JOINTS SCHEMATICALLY SHOWN SURVEYED DESIGN BY: DATE MagrJOW DRAWN KUAx? M.ttol SCALE K» - 1 . » vra - 1 • 9B BY. P DATTE REVISION nr DETAIL APHlOVtU DY AMHWaSTE DRAWING ML 3-1Ercr Dam & Irrigation Project ZCECE & CES 9.0 Foundation treatment 9.1 Surface Treatment After the cutoff trench of the required depth is excavated and stripping of the entire seat of the dam is completed, all loose or objectionable material should be removed by handwork, barring, picking, brooming, water jetting, or air jetting. Accumulated water from washing operation must be removed. Loose or unsuitable material occurring in cavities , shear zones, cracks, or seams should be removed according to the following criteria. • For openings narrower than 50 mm, cleaning is to be done to a depth of three times the width of the opening. • For openings wider than 50 mm and narrower than 1.5 m cleaning of the opening is to be done to a depth of three times the width of the opening or to a depth where the opening is 12 mm wide or less, but not to a depth exceeding 1.5 m Dental concrete is to be used to fill potholes and grooves created by bedding planes and other irregularities such as previously cleaned out shear zones, large joints, or buried channels. Comparatively fine cracks are to be treated with slush grout. Slush grout is a neat cement grout or sand - cement slurry used to fill narrow surface cracks But it should not be used to cover exposed areas of the foundation. The maximum particle size in the slush grout mixture should be no greater than one third the crack width. The consistency of the slush grout mix may vary from a very thin mix to mortar as required to penetrate the cracks. Before the placement of earthfill starts, the entire seat of the dam shall be compacted to increase density of the foundation soil as far as practicable. Earthfill placement procedures should ensure that specified earth materials are forced into intimate contact with the foundation surface and that adequate density is obtained Hand tamping compactors may , i be used to compact earthfill in or against irregular surfaces or abutments, potholes and depressions not accessible by heavy compaction equipment Annex A : Dani Final Detail Design Report/ 2009 36Erer Dam & Irrigation Project ZCECE & CES The abutments shall have to be suitably shaped and prepared in order to get good contact between the impervious core of the embankment and foundation. Overhangs should be removed. Flattening of the slopes is very much necessary because of the fact that differential settlement of the embankment may lead to tension along the upper portion of the dam and possible cracking along the longitudinal axis in the vicinity of the steep abutment slopes Further, differential settlement along the dam axis due to different compressibility characteristics of compacted fill material with the adjacent foundation soils may result into transverse cracks in the embankment which can lead to undesirable seepage condition. 9.2 Subsurface treatment Subsurface permeability is found to be ranging from 2.16 x 10'5 cm/sec to 3.26 x IO"*’ cm I sec in top 7m stratum of silty clay, sand mixed with gravel indicating that seepage loss is not going to be much But no permeability test could be conducted in course gravel and cobble zone below above said stratum in the river bed portion where the permeability appears to be quite high. The partial cutoff with upstream clay blanket can reduce the seepage but cannot stop it completely and that may result into piping It is therefore decided to go for positive cut- off It may be mentioned here that high saturated nature of groundwater exist in the foundation very close to the surface in the river bed portion and due to that it did not become possible to conduct permeability test in most of the bore holes In the light of the fact stated above and excessive depth of overburden in the river valley portion, excavation of positive cutoff trench in the deepest riverbed portion is found not feasible due to likely construction difficulties viz. heavy dewatering requirements and instability of sides of excavation etc. 0.6m thick plastic concrete diaphragm wall is found to be ideal type of positive cutoff in this particular reach of river valley portion since it is flexible and capable to deform under stresses in the surrounding soil. The plastic concrete diaphragm wall will undergo deformations compatible with those in the surrounding soil without development of cracks. But since the dam falls in high seismic prone area, the top portion of the diaphragm wall will be more vulnerable to damage during earthquqkc It is therefore decided to provide a partial cutoff trench 4m deep below impervious core so as to Annex A : Dam Final Detail Design Report/ 2009 37Ercr Dam & Irrigation Project ZCECE & CES_______ ______________________________________ keep the top of the diaphragm wall within impervious backfill of partial cutoff trench 2m below the ground level This will facilitate river diversion as planned through a temporary channel taken through river bed. A cover of plastic clay shall however to be provided around the top of diaphragm wall to safeguard against any possible damage to the wall or to impervious core. This cover of clay shall consist of relatively high plasticity with its liquid limit more than 50 The bottom of diaphragm wall should go at least 1.0m into rock. In the abutments, where the overburden zone is only about 7m, positive cutoff trench is provided The positive cutoff trench should be taken lm below fresh rock and overlap the plastic concrete diaphragm wall by at least 3m on its both ends. Depending on the water head of 34m at deepest river bed portion and overall depth of diaphragm wall being 19m or so, no further grouting of foundation rock is virtually required to be taken up in the fresh rock below diaphragm wall. A nominal 3m depth of curtain grouting is however provided in this reach also in continuation to that required in both the abutments. Details are shown vide Fig. 9.2 Annex A : Dam Final Detail Design Report/ 2009 38ELEVATION IN METER NOTES 1. All dimensions are in mm. 2. Ground profile os based on geotechnical investigation. 3. All loose soil, rock fragment debris and plants/trees/shrubs shall be removed. The depth of stripping is tentatively indicated to be 1m. However, the depth of stripping shall be decided by the Engineer incharge at the time of construction 4. The bottom level of cut-off trench is tentative based on giological profile. The depth of cutting at any particular location may vary depending on strata 5. The center line of cut-off is aligned 4.5 m U/S of dam axis. 6. Curtain grouting below cutt-off trench shall be extended not less than half hydraulic head. FEDERAL DEMOCRATIC REPUBLIC OF ETHIOPIA ministry of WATER RESOURCES CONCERT ENGINEERING ANO CONSULTING ENTERPRISE ASSOCIATION WITH CONSULTlNO ENGINEERING SERVICE ( INDIA ) PVT. LTD BROJECT;- ERER IRRIGATION project detail design TITVEs- stcnoN along o** WOW,MC rouNoxnoH treatment SURVEYED RY: DATE DRAWN SCALE *'*» - i. * __—______ D LSI GN AITROVED BY- FOATlt BY- .Mt'-®11 HLSTDON NR DHAWING NR DETAIL >1Ercr Dam &. Irrigation Project /CECE & CES 10.0 Internal Seepage Control Measures 10.1 Transition Filter I Inclined filter The dam being zoned earth fill dam with central clay core , the transition filters need to be provided both in the upstream and downstream of clay core since the specified gradation criteria is not satisfied between the adjacent zones i,e shell and core. Transition filters help to minimize failure by internal piping, cracking etc that may develop in the core or migration of fines from core materials Wider transition zone/ filters are recommended where cracks are likely to develop in the core due to differential settlement, earthquakes etc. and at the contacts with steep abutments. Considering the fact that the site falls in highly seismic prone area, 2m wide transition filter is suggested. The transition zone/ filter should be provided upto the top of core. The filter material to be used for drainage system shall have to satisfy the following criteria. Filter materials shall be more pervious than base material • Filter materials shall be of such gradation that particles of base material do not totally migrate through to clog the voids in filter material and; Filter material should help in formation of natural graded layers in zone of base soil adjacent to the filter by readjustment of particles. I he following limits are recommended as per USBR criteria to satisfy filter stability criteria and to provide ample increase in permeability between bases and filter (at least 10 cm/sec). These criteria are satisfactory for use with filters of either natural sand and gravel or crushed rock 1- D \^°f ,he Fll,er 2) (j of the base material 5 to 40 provided that the filter does not contain more than 5 percent of matenal finer than 0.074mm. Annex A : Dani Final Detail Design Report/ 2009 39Erer Dam & Irrigation Project ZCECE & CES 2. D lhe FlI,er _ 5 or less D ^Ie ^Jase materiai The grain size curve of the filter should be roughly parallel to that of the base material. In context to the design criteria of filter, it may be mentioned that considerable experimentation has been performed by the U.S Army of Corps of Engineers and the Bureau of Reclamation and others. Somewhat different sets of criteria are given by each of these authorities Merits and demerits of those are somehow inconclusive. The criteria given above is recommended not only for the reason that it satisfy filter stability criteria and provide ample increase in permeability between base and filler but also it is very simple to use for design of filters. In context to design and construction of transition I inclined filter, one more thing is felt necessary to be added and that is about segregation. In spite of taking sufficient care in placing of filter material, segregation sometimes cannot be avoided. To minimize segregation, filters should have relatively uniform gradation Filters with D^(F) less than about 20mm, do not generally segregate. Indian standard in this regard have worked out certain relation between D10(F) and to avoid segregation as furnished in Table-9 below This may be followed as far as practicable while designing the range of the filters. Table 10.1: Limits of Dio(F) and D90 (F) for Preventing Segregation SI No. (1) DI0(F) Min (mm) (2) D90(F) Max (mm) (3) (1) (2) 20 >) <0.5 25 i>) 0.5-1.0 30 iii) 1.0-2.0 30 iv) 2.0-5.0 40 v) 5.0-10 50 vi) 10-50 60 Annex A : Dam Final Detail Design Report/ 2009 40Erer Dam & Irrigation Project ZCECE & CES 10.2 Horizontal Filter It collects the seepage from the transition / vertical filter or from the body of the dam It also collects seepage from the foundation and minimizes possibility of piping along the dam seat. The horizontal filter is to be provided on stripped ground level. Depending on downstream topography, the slope of the horizontal filter towards the toe drain is to be decided. The horizontal filter must satisfy the following three requirements: • Gradation must be such that particles of soil from the foundation are prevented from entering the filter • Capacity of the filter must be such that it adequately handles the seepage flow from both the foundation and the embankment • Permeability must be great enough to provide easy access of seepage water in order to reduce seepage uplift forces The required thickness of the horizontal filter is quite small theoretically. But from practical consideration it is desired to provide here 1.0 m thick filter since the filter is to be designed to negotiate between foundation soil and rockfill material The criteria for designing the horizontal filter will be the same as transition filter stated above 10.3 Special Seepage Control Measures at Contact with Steep Abutments On the abutments, the seepage through the dam travel towards the foot of the embankment mainly through the transition/inclined filter At times there is concentration of seepage at the foot of the abutment if the length of such steep abutment is more. To prevent such concentration of seepage at the foot of the abutment, the impervious barrier of lm width with thickness equal to that of the horizontal filter may be put at suitable spacing depending upon the length of steep abutment/ ground The necessity of providing such barriers and their spacing etc. need to be decided by the site engineer after the final cutoff trench profile is arrived at, abutments are dressed and stripping below the seat of the dam is completed. Annex A Dam Final Detail Design Report/ 2009 41Erer Dam & Irrigation Project ZCECE & CES 11.0 Dam Instrumentation 11.1 General A simple scheme has been followed for instrumentation of Erer dam so as to evaluate the performance of dam during its operation and to verify the design assumption. To observe the behavior of dam and its foundation during construction and operation of the reservoir, the instrumentation is done to measure: • Settlements and movements • Pore pressures • Seismicity Internal Movement The measurement of internal movement primarily consists of measurement of vertical displacement and relative horizontal movements caused by the low shearing strength and the long term creep of the foundation or embankment material. Various instruments, using different techniques, for measurement, like cross arm settlement system, base plate settlement system, inclinometer system with biaxial probe, digital inclinometer etc, are available for measuring vertical & lateral settlement of embankment and foundation External Movement External movement of the dam crest or the side slopes accompanies internal movement of embankment and/or foundation. External vertical and horizontal movements are measured on the surface of embankments through the use of level and position surveys of reference point Reference points may be surface settlement points installed on the dam crest, slopes or toe of the embankment. Measurement of external movement of these surface settlement points is important for construction control as well as in monitoring the performance of the dam Annex A : Dam Final Detail Design Report/ 2009 42Erer Dam & Irrigation Project ZCECE & CES_________ ____________________________ Seismicity Surveillance of seismic environment of the project site needs special attention Seismographs and accelerographs to record micro seismic activities and strong ground motion can be installed at Harar meteorological observatory. No separate instrumentation is proposed at dam section to record seismic activities. Reservoir and tail water levels, wave height, evaporation and rainfall are some of the other parameters, which require to be separately monitored. 11.2 Instrumentation Scheme 11.2.1 General Scheme The general scheme of instrument in Erer Dam provides for measuring pore water pressures and internal movement at three cross-sections of dam embankment The three cross-sections are located at distances 514m, 834m and 1266m respectively from left bank The installation of monitoring instruments shall be carried out with great care under the supervision /guidance of instrument manufactures. 11.2.2 Measurement of Pore Water Pressures Pore water pressures in dam and foundation are proposed to be measured by means of vibrating wire electrical piezometers. Vibrating wire piezometers work on measuring the change in natural frequency of a stretched wire fitted in the transducer. The water pressure existing at the point of piezometer tip is transmitted to the circular membrane. The deflection of membrane changes the tension of the wire, which in turn changes the resonant frequency of the wire The change in resonant frequency of wire is read by means of a read out unit and is a measure of pressure change. ’It is proposed to install 23 Nos. vibrating wire piezometer^ in the dam foundation. Sixteen piezometers are installed in middle cross-sections at chainage514m and 834m while 7 piezometers are installed at ch. 1366m on the right bank of the river at the irrigation outlet. The pore water pressures within dam embankment shall be measured by means of 27 Nos piezometers, 10 each at the middle sections and 7 at the section on the right bank at irrigation outlet Annex A : Dam Final Detail Design Report/ 2009 43Ercr Dam & Irrigation Project ZCECE & CES The position of the three instrumented sections and the location of piezometers at these sections are shown In the relevant instrumentation drawings. 11.2.3 Measurement of Internal Movement It is proposed to use inclinometer system with biaxial probe for measurement of vertical and lateral displacement of dam embankment. A total of 4 inclinometers are proposed to be installed, along the dam axis at ch.514m and 834m. Internal horizontal movement of the embankment is proposed to be monitored by means of horizontal movement gauges, one each at the two instrumented sections in the river channel portion The position of inclinometers and horizontal movement gauges is shown on the drawings of dam instrumentation 11.2.4 Measurement of Surface Movements Surface movement of dam embankment shall be monitored by means of a number of surface settlement points, installed at dam crest The surface settlement points shall be installed on upstream face of the dam only above MDDL. A surface settlement point shall be made of 150 mm long, 25 mm dia, steel rod having a cross mark engraved at the top. The settlement points on lop of the parapet wall will be made of 25 mm dia, 150 mm long steel rod welded to a 225mm x 75 mm x 6 mm steel plate The surface settlement points shall be installed on the slopes near the crest, at the berm levels and at the heel & toe of the dam at chainage 600m, 800m & 1000m respectively. The settlement shall be monitored using a Total Station at regular intervals. The first reading acts as a reference and the subsequent readings give the settlement of the surface with respect to the time. Annex A Dam Final Detail Design Report/ 2009 44Ercr Dam & Irrigation Project ZCECE & CES 12.0 Bill of Quantities, Cost Estimates and Tentative Construction Schedule 12.1 Dam Appurtenance Works The Quantities of the various items of works related to the Erer dam have been defined with reasonable accuracy compatible with the present knowledge of the technical aspects of the project. The prices adopted for this report are current prices (December 2008) that are based on experience gained from similar projects being undertaken in the country. The bill of the quantities and cost estimate shall be used for the purpose of project worth analysis and to have an estimate of the project cost. The tentative construction period is estimated to be 36 calendar months as shown in the annexure. Annex A : Dam Final Detail Design Report/ 2009 45Erer Dam & Irrigation Project /CECE & CES REFERENCE 1. FDRE, Ministry Water Resource, Design guide line for Small and Medium embankment dams (Part I-E) ,2001 2. Indian standard: IS 8826; Guide lines for Design of large Earth and Rain fill dams. 3. William P.Creager Engineering for Dams, 1995 4. Water works Design and Supervision Enterprise in Association with Synergic Hydro (India) Pvt. Ltd, September 2007, Feasibility Report, Erer Irrigation Project, Volume 6 5. USBR: Design of small Dams, 1974 Annex A : Dam Final Detail Design Report/ 2009 46Annexure -1 • Design Parameters • Abstract of results for Stability Analysis • Stability Analysis Sheets 7 sheets • Seepage Analysis - 1 sheetJ _______________________________________ I ID [Task Name M1 ; M2 [M3 LIVM-L^ J 5 M6 I M7 ] M8 I M9 iMIOjMt 1 !M12|Ml3|M14[M15|M16iM17iM1BlM19]M20jM2l|M22iM23lM24|M25 16 5.2 CONSTRUCTION OF OGEE PART 19 5.3 CONSTRUCTION OF SLAB _______________ 20 5.4 CONSTRUCTION OF WALL 21 5.5 BACK FILL 22 6.0 MISCELLANEOUS WORK Project. ERER DAM & IRRIGATION M1= MONTH ONE Mllcslono Summary External Tasks External Milestone Progress Project Summary Deadline .V^'l Eh U > l.k I—Il......... ...Design Parameters S. No. Zone Sp Gr Unit Weight (kN/m ) 3 Permeability (cm/s) C’ O’ Remark 1. Core 2.64 17.9 3.9 x 10’8 20 29 2. Casing 2 2.64 18.5 5.0 x 10'3 00 32 3. Casing 2a 2.64 18.5 2.5 x 10^ 00 30 4. Filter 2.64 18.0 1.0 x 10'2 00 28 5. Foundation 1 2.65 16.0 1.0 x IO’5 25 20 Depth from 1.0 m to 6.0 m below Ground Level 6. Foundation 2 2.65 16.0 1.0 x 10’5 00 38 Depth from 6.0 m to 11.0 m below Ground LevelAbstract of results for Stability Analysis Cases Condition Factor of safety Permissible Factor of safety as per IS 7894 - 1975) Case I End of Construction (i) U/S (ii) D/S 2.075 1.475 2.040 1.467 2 092 1.476 1.0 1.0 Case II U/S Steady Seepage 1.788 1.607 1.672 1.5 Case III Sudden Drawdown (for U/S) 1.814 1.673 1.746 1.3 Case IV Steady Seepage (for D/S) 1.509 1.515 1.512 1.5 CascV Steady Seepage with Earth Quake (i) U/S (ii) D/S 1.009 1.050 — 1.004 1.011 1.051 1.0 1.0 1 Bishop Simplified Jnnbu Simplified Jnnbu CorrectedSafety Factor Case I. End of Construction US I 0.000 0.250 0.500 0.750 1.000 1.250 1.500 1.750 2.000 2.250 2.500 2.750 3.000 3.250 3.500 3.750 4.000 4.250 4.500 4.750 5.000 5.250 5.500 5.750 6.000 -T"-------------------------------- 1----- - o____Z___ $0 T_______ i»_________ jg____2____ __________ W &Safety Factor 0.000 0.250 0.500 0.750 1.000 1.250 1.500 1.750 2.000 2.250 2.500 2.750 3.000 3.250 3.500 3.750 4.000 4.250 4.500 4.750 5.000 5.250 5.500 5.750 6.000 Case I. End of Construction DS ft100 m Safety Factor Case II. Steady Seepage US a 8- 0.000 0.250 0.500 0.750 1.000 1.250 1.500 1.750 2.000 2.250 2.500 2.750 3.000 3.250 3.500 3.750 4.000 4.250 4.500 4.750 5.000 5.250 5.500 5.750 6.000g- ?- 8^ Safety Factor 0.000 0.250 0.500 0.150 1.000 1.250 1.500 1.750 2.COO 2.250 2.500 2.750 3.000 3.250 3.500 3.750 4.000 4.250 4.500 4.750 5.000 5.250 5.500 5.750 6.000 Case IV. Steady Seepage DS —r~ ------------- r-' ’-r- T----------------- - . • ------------------ r"----------- --------- r~i-------------------------- ■------------- 1----------------- -r ’----------------------- i---------------------- i----------------------------------- -v • ----------------r- -100m P__________ 50100________________________________ 150 200_ 250 300 350*oor Safety Factor g Case III. Sudden Drawdown (for US) 8- 8- 0.000 0.250 0.500 0.750 1.000 1.250 1.500 1.750 2.00C 2.250 2.50C 2.750 3.000 3.250 3.500 3.750 4.000 4.250 4.500 4.750 5.000 5.250 5.500 5.750 6.000 8- ► —I----- 400 m ’-T" -50 150 200 .250 300_____________ 350Safety Factor 0.000 0.250 0.500 0.750 1.000 1.250 1.500 1.750 2.000 2.250 2.500 2.750 3.000 3.250 3.500 3.750 4.000 4.250 4.500 4.750 5.000 5.250 5.500 5.750 6.000 I ► 0.15 r* ’ ▼ 0 075 ■ r- ------------------- ; •loom z50 "I........................... ..... ;----------------------------------------- 1------------ i - ■ - —r — ------------------------ — —,—f-r 0 50 100 150 200 250 300 .350Safety Factor 0.000 0.250 0.500 0.750 1.000 1.250 1.500 1.750 2.000 2.250 2.500 2.750 3.000 3.250 3.500 3.750 4.COO 4.250 4.500 4.750 5.000 5.250 5.500 5.750 6.000 I « 0 15 I ▼ 0 075 Case V. Steady Seepage with Earth Quake for US 50 100 150 300 350Pressure Head ooooooooooooooooooooooooo ino«nomoinoir>omo«no»nOino»noinoino«n ex 8 o -? E 8 os i
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