Coupled Analysis of Seepage and Slope Stability: a Case Study of Ribb Embankment Dam, Ethiopia

An earth-fill dam must be stable against seepage and slope failure for its intended function to be sustained throughout its service life. This study assesses the seepage and slope stability of the Ribb embankment dam. The stability of an embankment dam is determined by its shape, components, materials, qualities of each component, and thus the forces to which it is subjected. PLAXIS 2D software was used to conduct the analyses. The analysis covers the entire dam body, including 20 m of foundation depth, and the Mohr–Coulomb criterion was used to explain the behavior of both the body and the foundation of the dam. At various critical loading circumstances, the factor of safety, the quantity of seepage through the main body of the dam, and the foundation were tested. The flow rate, pore water distribution, and location of the phreatic line were all determined in this investigation. The phreatic line has appeared beneath the dam’s toe. This suggests that the dam is not vulnerable to sloughing difficulties, which are the most common cause of dam failure downstream. According to the simulation results, the average rate of seepage through the dam’s body at normal pool level was 5.05*10–6 m3/s/m, and the average rate of seepage through the dam’s foundation was 3.00*10–6 m3/s/m. The seepage results are within the permissible range, according to Look (2014). The results of the factor of safety were deemed insufficient due to the wide range of loading situations. The factor of safety values for both static and dynamic stability analyses at the end of construction were 1.3063 and 1.2226, respectively. Static stability analysis yielded a factor of safety of 1.2604 for steady-state conditions, and dynamic stability analysis yielded a factor of safety of 1.1803. The rapid drawdown condition is analyzed with a normal pool level of 1940 m lowered to 1900 m or rapidly reduced by 57% of the reservoir water. The static and dynamic evaluations revealed that the factor of safety was 1.2021 and 1.0662, respectively. The slope stability study of the Ribb embankment dam is safe under all critical loading circumstances, according to different approved design standards: United States Army Corps of Engineers (USACE), British Dam Society (BDS), and Canadian Dam Association (CDA).