Impact Of Drawdown Speed On Slope Stability Of Tendaho Dam Under Static And Pseudo Static Earthquake Loading Condition

Dams are hydraulic structures used to store, control, divert water impounding it behind the upstreamrnside of dam in a reservoir for different purposes, like hydropower generation, water supply,rnirrigation, navigation and transportation, etc. Although dams have many advantages, the risk thatrnmay happen due to the failure still exists. rnOne of the most dangerous conditions causing failure of earthen dams’ upstream slope is speed ofrndrawdown condition when the countervailing upstream water pressure has disappeared with fastestrnspeed; it causes a danger to the upstream slope. rnIn this work Tendaho earthen dam, low permeability construction material, which is located on the rnhighly seismically active zone, Eastern Ethiopia Rift Valley was studied. The overall objective of the rnstudy was assessing the impact of drawdown speed on Slope Stability of Tendaho dam under staticrnand pseudo static earthquake loading Condition by using different methods. Traditional limitrnequilibrium methods and a finite element software, GeoStudio 2007 and 2012 computer programrnwere utilized in the slope stability analysis. Seep/w, Slope/w and Sigma/w GeoStudio sub programrnwere used to analysis and develop pore pressure curve and factor of safety curve for purpose ofrnreservoir water level operation monitoring. rnThe developed factor of safety curve shows that safety of upstream slope of the dam decrease duringrndrawdown condition and seismic load effect. The upstream slope of Tendaho dam is stable duringrndifferent drawdown speed and reservoir water level fall from FRL to MDDL. But, the worst casernscenario occurs when reservoir water falls below 387m from FRL (408m) within recommendedrnvalues of evacuation periods. In addition, during earthquake force was applied to the model therncritical drawdown level and evacuation period is 394m and 40 days, respectively. It is also found that rndrawdown situation of Tendaho dam under reservoir operation have not affect on upstream slope ofrnthe dam and emergency drawdown is not required till now. However, assessing the dam slopernstability under different drawdown speed and earthquake loading condition is important to avoid thernupstream slope sliding during drawdown condition in the future.

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