Bearing capacity and failure of footing on anisotropic soil: A multiscale perspective

Abstract Fabric anisotropy underpins the mechanical response of granular soils pertaining to a wide range of practical geotechnical applications. This paper presents a multiscale computational study on a strip footing resting on an anisotropic soil foundation. The focus of this study is placed on examining the cross-scale links of key grain-scale mechanisms in the soil that underscore interesting macroscopic observations of the footing problem over a full loading range from peak to large deformation regimes until its failure. We employ a hierarchical coupling of Material Point Method and Discrete Element Method (MPM-DEM). Mesoscale ensembles consisting of elliptical particles with specific alignments to represent bedding planes in anisotropic soils are generated. They are embedded into the material points of the MPM and serve as Representative Volumetric Elements (RVEs) with solutions by DEM to extract nonlinear material responses in solving the footing as a boundary value problem that may undergo large deformation to failure. The study confirms experimental observations that the bearing capacity of the strip footing decrease with the bedding angle α . It shows that ignoring fabric anisotropy for soil may lead to a significant overestimation or underestimation of the bearing capacity in extreme cases. The final failure patterns for all anisotropic cases feature general failure modes with two major slip surfaces, and they are predominantly in an asymmetric manner except the horizontal bedding case and the isotropic case. The degree of asymmetry in the failure pattern shows a correlation with the bedding angle. These observed features are further corroborated with microstructural analyses on the evolution of different sources of fabric anisotropy in slip surface.