Risk assessment of soil slope failure considering copula-based rotated anisotropy random fields

In natural slopes, apart from isotropic and transversely anisotropic soil fabric, rotated anisotropic soil fabric is also commonly observed due to deposition and weathering. Previous studies mainly focused on the effects of copula selection on transversely anisotropic soil slope stability. However, the influence of copula selection on rotated anisotropically deposited soil slope stability is still not clear. This study develops a new method to generate copula-based rotated anisotropy random fields for characterizing the spatial variability of soil properties. The index associated with the failure probability and consequence is employed to assess the risk of failure of two cohesive-frictional slopes in spatially variable soils (i.e., a single- and a two-layer slope). The results reveal that the commonly-used Gaussian copula may underestimate the risk of failure of both the single- and two-layer slopes at any soil deposition orientation. The risk of slope failure calculated by four candidate copulas shows a great difference. This difference is mainly affected by slope failure probability. For a single-layer cohesivefrictional slope, the slope with the highest risk of failure occurs at a rotational angle beta = 150 degrees. The corresponding soil deposition orientation (30 degrees) is slightly smaller than the slope inclination (45 degrees), independent of copula types. Additionally, when a slope fails, it can be found that the Gaussian copula corresponds to the largest sliding volume for some combination anisotropy cases, which is in reverse to the failure probability. Therefore, for a cohesive-frictional slope, it is suggested to consider both failure probability and failure consequence to assess the potential slope failure risk. Furthermore, the No.16 copula can give a more conservative risk assessment when dependence structure between cohesion and friction angle is uncertain.