ABSTRACT
Safety assessment of earth slopes is often carried out using the factor of safety or the reliability index based on a particular slip surface. The inadequacy of using a particular slip surface is well known because it does not consider the system aspect of the slope. Further, slopes that have been in service for some time have been load tested. Their successful survival is evidence that their capacity is greater than load effects or their shear strength is greater than their mobilized shear strength. This information should also be considered in assessing the safety of existing slopes as well. Both the reliability analysis and the reliability updating are presented in the present study.
For the reliability analysis widely used first order reliability method is employed for estimating the probability of failure or reliability index. Since the failure of any slip surface implies failure of the slope, the slope can be considered as a series system. In the reliability analysis, this system aspect of the slope can be dealt with by defining a limit state of the system as the minimum of the ratios of the shear strength to the mobilized shear strength for each of all potential slip surfaces minus one. The reliability updating analysis of existing slopes incorporates the information on the safe performance of existing slopes. The proposed approach is illustrated by two simple numerical examples.
