STABLITIY OF SLOPE AND SEEPAGE ANALYSIS IN EARTH FILL DAMS USING NUMERICAL MODEL: ACASE STUDY OF DORA EMBANKMENT DAM, TIGRAY, ETHIOPIA

Abstract

To attain the primary objective of seepage and slope stability analysis, the study has been carried out based on primary and secondary data of Dora earth fill dam. The causes of seepage problem have been identified using geophysical investigation report data of the embankment and foundation, design document, site investigation and construction history of the dam. Geo studio software is one of geotechnical program that is based on the finite element and can consider analysis like stress-strain, seepage, slope stability, dynamic analysis and also fast water drop in reservoir by assuming different mesh size. In this research Geo studiosoftware has been used to calculate seepage and slope stability of Dora earth fill dam. In this study seepage analysis has been done by seep/w software model to evaluate the total f low rate through the dam cross section using three cases of seepage analysis conditions. And case three or seepage analysis at normal pool level based on the rearranged soil hydraulic conductivity material is selected for further analysis and to put some mitigation measure and the result show that average flow rate of leakage under the case using different mesh size including foundation seepage is equal to 0.079m 3 /s for the entire length of the dam. This value is compared with the quantity of seepage estimated practically at the down stream that is 0.072m 3 /s. Therefore, the practical measurement almost has some uncertanity of quantifying the expected quantity of seepage. To this end, problem of seepage at the downstream face of the dam which are threatening the dam stability are expected to result from geology where the dams are located and the method of investigation coupled with lack of experience in data collection and analysis and also considering the construction history are the major factors attributed to this problem. And Slope/W softw are is also used under different conditions to evaluate slope stability calculation for each state and each slope with Bishop, Janbu, ordinary method of slides and GLE methods is calculated and compared with the minimum acceptable safety factor provided from United States army of Corps in each of these methods, beconsidered as a safety factor of slope stability. To alleviate the seepage problem, upstream impervious blanketing, downstream berming and Provision additional shoulder at the dawn stream dam surface with clayey gravel soil construction are the proposed remedial measures.