Seepage and Stability Analyses of Earth Dam Using Finite Element Method

Abstract

Dams are mainly constructed of earth and rock-fill materials and hence they are generally referred to as embankment dams or fill-type dams. Earth-fill dams are simple structures which are able to prevent the sliding and overturning because of their self weight. Due to lack of suitable clay materials, sometimes the dams are designed as zoned core that is composed of three vertical zones including central impermeable core and two permeable shells on either sides of the core. A failure of earth dam is attributed to the following: hydraulic failure, seepage failure, piping through dam body and structural failure due to earthquake. The design and construction of an earth-fill dam is one of the key challenges in the field of geotechnical engineering, because of the unavoidable variation in foundation condition and the properties of the available construction materials. A homogeneous earth-fill dam should be designed with relatively flat slopes to reduce the risk of failure. The practical seepage problems are not easily convertible into an equivalent numerical counterpart because of the heterogeneity of the natural soils and the varying boundary conditions. The role of drainage system is also vital as it shifts the phreatic surface ensuring the safety of downstream toe. This paper presents the results of seepage and stability analyses of the considered earth dam using finite element method. The seepage analysis is divided into two categories viz. Steady state and Transient analyses. Based on the parametric sensitivity analysis, both the seepage and stability studies have brought out the importance of considering the coupled effects on the overall stability of the earth dam. It is concluded that the coupled analysis is a prerequisite for the design and performance evaluation of the earth dam under all conditions of seepage and stability. The study shows that increase in the Young's modulus of core and shell resulted in the decrease of the maximum crest displacement and the variation in angle of internal friction plays a vital role in the fulfilment of the overall stability criteria. The slope of 1V:2.5H was adopted for both the downstream and the upstream sides. The factor of safety (FS) was greater than 1.6 for both the full (high) reservoir condition and low reservoir condition whereas, the FS values were found to be less than the stipulated values for the other stability considerations.