Reliability of spatially variable undrained slopes -

Abstract

Conventionally, the stability of a soil slope is evaluated by adopting a deterministic approach that is based on a target global factor of safety that is calculated either through limit equilibrium methods or through numerical analyses. Slope stability analysis is a branch of geotechnical engineering that is highly amenable to uncertainties. Spatial variability and model uncertainty are considered the major sources of geotechnical uncertainties. To account for such uncertainties in slope stability problems, numerous steps have been undertaken in recent years to adopt a probabilistic stability analysis that considers the uncertainties of soil properties in a systematic manner. However, there is currently an inconsistency in the evaluation of the spatial uncertainty and no accounting of the model uncertainty in the analysis. The primary objective of this thesis is to provide slope stability investigators with a robust reliability analysis that takes into consideration the combined uncertainty of spatial variability and model uncertainty. To achieve this objective, a thorough investigation is conducted to evaluate the model uncertainty of common slope stability models (ex. Bishop, Ordinary Method of Slices, Janbu, and Spencer) by assembling and analyzing a database of historical failures of slopes. The database is also used to investigate the possibility of a lower-bound factor of safety for undrained slopes and its impact on the reliability of slopes. The model uncertainty and the uncertainty due to spatial variability are then combined within a reliability-based design framework to recommend design factors of safety that would result in acceptable probabilities of failure for undrained slopes.