Probabilistic stability analyses of undrained slopes by 3D random fields and finite element methods

A long slope consisting of spatially random soils is a common geographical feature. This paper examined the necessity of three-dimensional (3D) analysis when dealing with slope with full randomness in soil properties. Although 3D random finite element analysis can well reflect the spatial variability of soil properties, it is often time-consuming for probabilistic stability analysis. For this reason, we also examined the least advantageous (or most pessimistic) cross-section of the studied slope. The concept of “most pessimistic” refers to the minimal cross-sectional average of undrained shear strength. The selection of the most pessimistic section is achievable by simulating the undrained shear strength as a 3D random field. Random finite element analysis results suggest that two-dimensional (2D) plane strain analysis based the most pessimistic cross-section generally provides a more conservative result than the corresponding full 3D analysis. The level of conservativeness is around 15% on average. This result may have engineering implications for slope design where computationally tractable 2D analyses based on the procedure proposed in this study could ensure conservative results.