Simplified probabilistic slope stability design charts for cohesive and cohesive-frictional (c-φ) soils

Design charts to estimate the factor of safety for simple slopes with cohesive-frictional (c-phi) soils are now available in the literature; however, the factor of safety is an imperfect measure for quantifying the margin of safety of a slope because nominal identical slopes with the same factor of safety can have different probabilities of failure due to variability in soil properties. In this study, simple circular slip slope stability charts for phi = 0 soils by Taylor in 1937 and c-phi soils published by Steward et al. in 2011 are extended to match estimates of factors of safety to corresponding probabilities of failure. A series of new charts are provided that consider a practical range of coefficient of variation for cohesive and frictional strength parameters of the soil. The data to generate the new charts were produced using conventional probabilistic concepts together with closed-form solutions for cohesive soil cases, and Monte Carlo simulation in combination with conventional limit equilibrium-based circular slip analyses using the SVSlope program for c-phi soil cases. The charts are a useful tool for geotechnical engineers when making a preliminary estimate of the probability of failure of a simple slope without running Monte Carlo simulations.