Reliability Analysis of Slopes in Soils with Strain-Softening Behaviour

This article presents a systematic approach for the reliability analysis of slopes in strain-softening soils based on the first order reliability method (FORM). The performance function is based on the Spencer method modified to take strain-softening into account in terms of the average residual factor R_F over a potential slip surface estimated based on a simple progressive failure model available in the literature. The shear strength parameters, peak and residual, are assumed as normally distributed random variables and the reliability analysis is performed on the probabilistic critical slip surface. For the residual factor R_F, bounded by 0 and 1, a generalized beta distribution has been assumed. Results obtained from an illustrative example indicate that a significant reduction (25%) occurs in the value of the minimum reliability index when R_F is considered as a random variable compared to when R_F is considered as a deterministic parameter. A FORM based sensitivity study also reveals that, amongst the five random variables, residual factor has the most dominating influence on the estimated reliability index and thus justifies its inclusion as one of the random variables.