Modelling a granular bentonite system as a discrete set of continuum units

Abstract

A model is proposed to describe the hydromechanical behaviour of granular bentonite systems. Its formulation is based on abstracting the system as a discrete set of bentonite units, which form continuum sub-domains where homogeneous behaviour is assumed. This allows the mass balance of each unit to be characterised in an integrated way, in addition to applying advanced double porosity-based models with relative simplicity to describe its stress–strain behaviour. As a first approach, the liquid flow in the megapores between the units is approximated with an advective–diffusive continuous medium formulation. The contact between units is modelled using a strut scheme. To evaluate the scope of the model, the hydration of a granular bentonite specimen has been reproduced. Without introducing material parameters additional to those used in double porosity models, very satisfactory results have been obtained when modelling the evolution of the integrated behaviour of the whole sample (swelling pressure and total water mass increase) as well as the evolution of the distribution of water content, dry density and local vertical displacements. The model has demonstrated its consistency by maintaining the quality of the fit regardless of the significant decrease in megaporosity. In addition, the results illustrate the capability of the formulation to introduce the effect of friction and of the initial heterogeneity of the system into the model. For this reason, and although the scope of the formulation must be evaluated in a wider range of cases (non-isothermal conditions, non-negligible salinity, high porosity granular systems), the model is a tool of interest for the analysis of the homogenisation of granular bentonite systems.