Multiscale modelling and analysis of footing resting on an anisotropic sand

The influence of the inherent fabric anisotropy of sand and its evolution on the footing bearing capacity and failure mechanism has been modelled and analysed with a multiscale approach that couples the finite-element method (FEM) and the discrete-element method (DEM). In this approach, the material constitutive responses are captured by DEM simulations on representative volume elements (RVEs) assigned to the FEM Gauss points. The inherent fabric anisotropy of sand is reflected by the bedding plane angle α of the RVEs composed of elliptic particles, where α measures the average angle between the long axes of the particles and the horizontal direction. The bearing capacity is found to decrease with an increasing α and the reduction can reach as high as 25%. Asymmetric deformation has been observed in the α other than 0° or 90° cases, which is mainly attributable to the different relative principal directions between the stress and the fabric at the two sides of the domain. Further multiscale analyses reveal that the load-bearing structure of the material expressed by the contact-normal-based fabric tensor is more fragile under the footing loading at one side of the domain and in larger α cases, which offers a micromechanical explanation to the observation of the asymmetric deformation and the decreased bearing capacity with increased α.