A Comparative Evaluation of Seepage, Slope Stability and Deformation in Embankment Dam :- The Case of Aguat Wuha Micro Earthen Dam Ethiopia

Abstract

This study presents an evaluation and comparative study on the seepage, slope and defor mation analysis of Aguat wuha micro earth dam which is found in the Amhara Region, south Wollo Zone, Saint Ajibar Woreda. The main problem of Aguat wuha micro earh dam is anticipated seepage through the dam body, foundation, and surrounding outlet construction of the dam. The aim of this study is to identify the problem of Aguat Wuha Embankment dam by evaluating seepage, slope stability, and stress deformation. The main significance of this study is protecting the loss of stored water and safe guarding the safety of the dam and thus protecting down stream dwellers and property from hazards. The analysis was performed using limit equilibrium (Geo Studio) and finite element (Plaxis 2D 8.2) models. Field data measurements and observatory investigations were also carried out. Seepage analysis suchas:- seepage magnitude, pore water pressure distribution, and location of the phreatic line have been determined using the limit equilibrium analysis of SEEP/W and finite element analysis of PLAXIS models. From the simulated results of SEEP/W and PLAXIS models at 2874m a.m.s.l, the average seepage rate for the entire length of the dam at full reservoir level was found to be 1.17??10-5 m3/s and 4.987??10-3 m3/s respectively;-, whereas for 2868m a.m.s.l, reservoir level was equal to 5.5??10-6 m3/s and 3.576??10 -3 m3/s respectively;-, and the practical measured seepage value (rectangular lined masonry canal) usning manning equation at the downstream of the dam body at 2874m and 2868m a.m.s.l, was 7.89??10-3m3/s and 6.23?? 10-3 m3/s respectively. where as using calliper container method the meas ured value was 9.4??10-3 m3/ s and 8.1??10-3 m3/s at 2874m a.m.s.l and 2868m a.m.s.l respec tively. The stability analysis results for the designed conditions show that the slopes are un stable under some of the loading conditions of the Plaxis 2D 8.2 model which is the factor of safty result is less than 1.3 but for Geo Studio 2012 the slopes are stable under all loading conditions which means the factor of safty value is greater than 1.3. However, the actual site condition of the dam stability analysis indicated that the downstream slope is stable. The results of stress-deformation analysis (maximum horizontal and vertical displacements), carried out using both SIGMA/W and PLAXIS models, for end-of-construction and full res ervoir conditions show almost similar values. The maximum vertical displacements 0.1718m occurs at the crest of the dam, which is 0.625% of the dam height. This study shows that the Plaxis 2D 8.2 model simulatesseepage better than Seep/W, whereas the two models haveclose capability in simulating deformations. From thisstudy, we also understand that the damsafety and performance currently is not satisfactory (high leak, slope instability and defor mation problems). Hence, it is recommended to conduct critical monitoring and surveillanceof the dam and It is also better to use updated PLAXIS as an alternative to LEM because it presents several advantages that are no assumptions are needed concerning the failure sur face, no assumptions on the inter-slice side forces are needed, since there is no concept ofslices and soil behavior can be modeled in terms of stresses-strains.