SEEPAGE AND SLOPE STABILITY ANALYSIS OF EARTH FILL DAM USING NUMERICAL MODELING, THE CASE STUDY OF DORA DAM, NORTHERN TIGRAY, ETHIOPIA

Abstract

Embankment dam failure may occur due to different reasons such as structural instability conditions, hydraulic conditions, seepage through the dam body and foundation. The determination of factor of safety for the dam slope stability, under different cases of operations, is vital to ascertain the dam overall safety. In this thesis, Finite Element modeling is employed for simulating seepage and slope stability analysis of earth dam problems using Geo Studio software. The model is verified, and then it is employed to analyze seepage and stability of Dora Dam. Three different cases of operation are considered; end of construction before filling the reservoir, steady state seepage and rapid drawdown of the reservoir. Four major analytical methods there used to assess the stability of the dam side slopes; Morgenstern-Price, Bishop, Janbu, and Spencer. The results of the analysis presented in this paper confirm the safety of Dora dam against combined seepage and slope stability under all cases of operation. The result of stability analysis performed showed that all parts of the dam are safe within the prescribed range of factors of safety for the possible all loading and operation cases. But all the critical slip surfaces pass through the dam shell which indicates that this zone represents the weaker zone and it needs spatial attention. The result of seep/w analysis showed that 0.01899853 m3 /sec seepage loss during steady state case and 0.019846008 m3 /se seepage loss through the dam during transient analysis. The factory of safety of 1.795 for downstream slope during steady state, and 1.433 during sudden draw down are among the results found. The analysis result shows that the water tightness of the dam, stability of the embankment slope has in this thesis performed in a better way for some loading conditions like downstream slope at steady state, construction stage