SLOPE STABILITY ANALYSIS OF AN EARTHEN EMBANKMENT DAM

Abstract

The slope stability analysis of an earthen embankment dam has been conducted under various conditions to assess its stability and resistance to potential failure. The analysis considered the end of construction condition, partial reservoir pool condition, sudden drawdown condition, steady state seepage condition, and earthquake condition. Under End of Construction conditions, both upstream slope as well as downstream slope have been analysed. It is assumed that the reservoir is empty, and the river is flowing at tail water level. The analysis results indicate that the dam meets the required factor of safety and remains stable under normal operating conditions at the end of construction. Under Partial reservoir pool condition, the reservoir water is not at its maximum level and has been assumed at 270 m. Steady seepage conditions are assumed to be achieved. Under this condition, the upstream slope is critical and therefore, only upstream slope has been checked for slope stability. The analysis results indicate that the upstream slope is safe under partial reservoir pool conditions. Under rapid drawdown conditions, the upstream slope is more likely to fail and therefore, only upstream slope has been checked for slope stability. The analysis has been done using two approaches namely, simple effective strength approach and rigorous effective strength approach. In Simple effective strength approach, the drawdown is assumed to be instantaneous wherein the reservoir water level recedes from maximum water level to minimum drawdown level in almost nil time. This represents the worst scenario from the slope stability point of view. Under rigorous effective strength approach, it is assumed that the steady-seepage conditions have been achieved and the reservoir water level recedes from maximum water level to minimum draw down level in a period of 180 days. The analysis results indicate that the dam is safe under gradual drawdown condition but is critical under instantaneous drawdown condition.