Numerical modelling of expansive geomaterials: Finite element formulation and constitutive models

The successful simulation of the behaviour of expansive soils using FEM strongly depends on the acting hydromechanical processes and their proper consideration. During swelling processes, part of the pore water is bound to the solid. However, the associated change of volume fractions in the porous medium and its contribution to the overall material behaviour is not accounted for in most numerical frameworks. In this paper, a numerical framework based on the Theory of Porous Media (TPM) and a three-dimensional hydro-mechanically coupled hypoplastic constitutive model for expansive soils are proposed. The TPM includes a distinct swelling water phase that does not participate in the flow through the pore space. A bidirectional mass transport enables the transition from free to swelling water during change in water content. By consistent balancing in the governing equations, the swelling induced reduction of hydraulic conductivity is directly accounted for. The performance of the proposed framework is demonstrated by back calculation of laboratory tests on different materials. Its capabilities to simulate complex loading paths in (un)saturated conditions with a single set of parameters are shown.