Probabilistic analysis of soil nails placed in random soil fields with rotated anisotropic strength

Soil nails used to support excavations may be inserted into soils with bedding structures at different orientations. This paper examines for the first time the influence of such cases on probabilistic margins of safety for a typical soil nail arrangement by assigning rotated anisotropic random fields of soil strength parameters that are aligned with the bedding structure of the soil domain. The results using rotated anisotropic random fields on statistical outcomes for the computed global factor of safety are compared to results using homogeneous and isotropic random fields, and deterministic analyses. Analyses using rotated anisotropic random fields show that there is a detectable worst bedding direction that gives the highest probability of failure. However, the range of factor of safety for all random field cases is small and remains in the vicinity of the deterministic value. This is ascribed to the ability of the soil nails to anchor the entire reinforced soil domain together and prevent preferential failure paths to develop through the soil. The paper includes the calculation of the confidence in the point estimate of probability of failure for different conditions, and lessons learned in selecting domain size and level of discretization using the random finite difference method.