Modelling mesh independent failure loads of a soft strain-softening clay using a rate dependent model

Abstract

If no regularisation method is used during finite element modelling of strain-softening (brittle) materials, results become mesh dependent: manifesting as very thin shear bands whose thickness and orientation depends on the mesh discretisation. The objectives of this paper were to determine if mesh independent results were achieved, and to track the evolving width of the shear band when considering naturally occurring properties of soft clays, including a rate dependent stress-strain-strength relationship. The constitutive model included a destructuration process and strain-rate dependency, and the analyses allowed for local pore water flow. A bearing capacity problem was loaded to failure. Analyses were conducted with different mesh discretisation, loading rates and permeabilities. The results demonstrated mesh independent failure loads, and the strain-softening occurred in zones with thickness independent of mesh size. Local pore water flow delayed the initiation of strain softening and resulted in higher failure loads. The softening zones grew in thickness to over one meter, reinforcing that the finite element method is suitable for the determination of the bearing capacity of strain-softening sensitive clays. In conclusion, the rate dependent constitutive model is a promising method for regularising strain localisation in soft brittle clays under quasi-static loading conditions.