Projection method for validating reliability analysis of soil slopes

The mean-value first-order second-moment (MFOSM) method is the main method for estimating the reliability of slopes in practice. It is well recognized that the method occasionally underestimates the probability of failure for inhomogeneous soil slopes, but there is as of yet no commonly accepted procedure to identify this problem. This study presents a solution by projecting MFOSM results to obtain an equivalent most probable failure point in the material space as defined by Hasofer and Lind. A stability analysis using this material point then provides a check for the validity of the MFOSM solution. If the resulting critical factor of safety is one, the MFOSM results are valid; whereas, if a factor of safety of less than one is obtained, the reliability index is overestimated and the failure probability underestimated.