Probabilistic “ φ = 0” stability analysis in strain-softening soil

Abstract

A key issue in the improvement of geotechnical analysis and design is the assessment of safety and reliability. The value of probabilistic basis for risk assessment is now widely recognised. In this paper, attention is focussed on strain-softening behaviour which may be, and often is, overwhelmingly important for progressive failure. Other factors may also be significant but these are not dealt with here so that the formulation is simple enough to appeal to the geotechnical practitioner. After discussing the importance of strain-softening behaviour under undrained conditions, a method for determining the probability of failure is proposed so that widely available stability charts can be used. Peak and residual shear strengths (undrained) are regarded as the only random variables. The concept of “residual factor” is used to specify the proportion of slip surface which has passed from peak to residual shear strength. The progression of failure is seen in terms of an increasing proportion of the slip surface passing to the residual strength state. The proposed method is applied to an illustrative example using three different probability distributions or models.