Importance of Sand Fabric Anisotropy on Fault Rupture-Foundation Interaction

For the design of structures with shallow foundations in the vicinity of active faults sophisticated numerical analyses are a prerequisite. Current practice employs isotropic constitutive models for the simulation of the foundation soil layer. For enhanced accuracy, these models may also include strain softening, as well as a non-associated flow rule if this soil is granular, but the anisotropic nature of soils is not considered. In order to study how much sand fabric anisotropy affects the fault rupture-foundation interaction problem, this paper employs the finite difference method and 3 constitutive models of various complexity, including a new fabric-based model for sand named SANISAND-FR. All models are calibrated to give identical results under triaxial compression. The analyses show that the assumption of isotropy affects significantly the fault rupture–foundation interaction, and hence the expected response of the structure (e.g. rigid body rotation) due to rupture surfacing. This means that the design of structures against fault rupturing is of doubtful accuracy if models are used that do not consider sand fabric anisotropy.