Modified Semi-Analytical Method for 3D Slope Reliability

Abstract

An improved method for the reliability analysis of 3D slopes has been proposed based on the semi-analytical method of Vanmarcke (1977). Comparing the predicted responses of an idealised 3D slope obtained by the more general, albeit computationally intensive, random finite element method (RFEM), and the original semi-analytical method showed that the latter gives unconservative estimates of the probability of failure. Three significant areas were identified as requiring improvement in the simpler method. These were corrected by: (i) a correction factor to reduce the overestimation of endresistance in 3D failures, i.e. reducing the impact of conservative geometric assumptions; (ii) a correction factor to correct for overestimating the average shear strength on the failure plane, which is found to be lower than the average shear strength for the entire slope; and (iii) an alternative relationship for the expected failure length for intermediate values of the spatial correlation length of the shear strength. The proposed modified semi-analytical method gives substantially improved results that are comparable to RFEM, while retaining the simplicity of the original method.