Stability Analysis of Dyke Using Limit Equilibrium and Finite Element Methods

Abstract

The present study illustrates the slope stability analysis of dyke using limit equilibrium and finite element methods. Stability analysis of the dyke has to be carried with the methods practiced for earthen dam. The stability of the dyke is analyzed using limit equilibrium (SLOPE/W) and finite element (PLAXIS 2D) methods under different construction stages and different operating conditions. The three different conditions viz. stability of dyke just after the end of construction, after deposition of the bottom ash and empty on the other side and rapid drawdown of water on the bottom ash side are assessed. The flow in the third case is unconfined due to the unknown phreatic surface and the unknown nature of the seepage. The variation of phreatic line plays a vital role in the safe performance of the dyke, hence it has to be critically evaluated so that it does not cut the downstream toe of the dyke. In the SLOPE/W software, the Morgenstern-Price method is made use of in the evaluation of factor of safety. The factor of safety has also been evaluated using the PLAXIS 2D software making use of the strength-reduction technique. A typical example considered was the earth dam i.e., dyke having dimensions of 14 m height, 6 m crest with slope of 1V:2H on both the upstream and downstream sides. The subsoil was of soft disintegrated rock (SDR) for a depth of 2 m and underlain by hard rock strata for a depth of 8 m. The factors of safety evaluated for different stability conditions of the dyke have highlighted the importance of considering them separately. Based on the results, it is noted that the most critical among all the conditions is the sudden drawdown case followed by the steady seepage which is critical for the downstream slope of the dyke.