Modeling of soils as multiphase-materials with Abaqus

Soils are mixtures of three phases, a porous soil skeleton of solid mineral particles and two fluids water and air filling the pores completely. The soil skeleton and the fluids can move depending on the constitutive behaviour of all constituents and interactions between them. In general a coupled deformation/seepage problem exists which can be uncoupled for certain circumstances. Mechanical models of soils are based on continuum mechanics or particle mechanics. The continuum approach requires a mixture theory, uncoupled problems require the classical continuum mechanics for single-phase materials only. Abaqus has built-in features to carry out uncoupled deformation or coupled deformation/seepage analysis for saturated and unsaturated soil which are described in this paper. Further models and analyses will be shown applying a user subroutine of type UEL. In this model an elastic or hypoplastic stress-strain relation for the soil skeleton is assumed. The user subroutine is applied in some case studies, results will be compared to Abaqus built-in analyses if available.