Quantifying and modelling fabric anisotropy of granular soils

This paper describes an integrated study of the effects of fabric anisotropy on granular soil response, in which the microscopic measurements are properly linked with the macroscopic modelling. Using an image-analysis-based technique and an appropriate mathematical approach, the inherent fabrics of sand specimens prepared in the laboratory using different sample preparation methods were measured, quantified and compared at a microscale level. It was found that the specimen prepared by the dry deposition method had a more anisotropic microstructure than the specimen prepared using the moist tamping method, which is considered directly associated with the experimental observation that different sample preparation methods produce samples with distinctive responses under otherwise identical conditions. An existing platform model was then extended so that the combined effects of initial fabric and shear mode dependence were accounted for in a simple yet rational manner. To calibrate and verify the model, a series of laboratory tests was conducted for Toyoura sand under various combinations of loading and sample preparation conditions. It is shown that the model is capable of simulating in a unified manner the experimental results reflecting the combined effects of sample preparation methods, loading paths, soil densities and confining pressures.