Seepage and Slope Stability Analysis of Earthen Dam: A Case Study of Lebu Dam, Ethiopia

Abstract

Seepage and Slope stability are a matter of remarkable concern in the construction of earthen dams where the failure of slopes may incur a severe loss of life and damage to property. The most important factors that cause instability of slope and lead to failure are gravitational force, the force due to seepage of water, sudden lowering of water adjacent to a slope and force due to earthquake. This study aims at analyzing the static slope stability of Lebu Dam using the finite element method. The analyses were carried out using PLAXIS 2D software employing and the Mohr-Coulomb elastic-plastic constitutive model to define the behaviors of the dam materials. The safety factor values, the quantity of seepage through the main body of the dam and foundation, displacements, were carried out at different critical loading conditions. In this study, seepage analysis, such as Flow rate, pore water distribution and location of the phreatic line were determined. Additional actual field data measurements were also carried out. From the simulated results the quantity of seepage through the embankment of the dam during NPL was equal to 0.010 /s and through the foundation of dam was 0.004975 /s. Total the quantity of seepage through the embankment dam during the CRL is 0.00627 /s. whereas, the actually measured quantity of seepage accumulated at the downstream of the dam during CRL was 0.0127m³/s. Using recommended design standards: USACE, USBR and British Dam Association the slope stability analysis of the Lebu earth dam at all critical loading conditions is safe.

Keywords:Finite element method, Seepage, Stability analysis, PLAXIS 2D