Swelling and mechanical erosion of MX-80 bentonite: Pinhole test simulation

• We propose an approach to simulate the coupled swelling and erosion of bentonite.
• The bentonite mass loss is described with a simplified erosion model.
• The deformability of bentonite is described with a double-porosity formulation.
• The simulation of pinhole tests on MX-80 samples yielded satisfactory data fits.
• The proposed method is useful for simulating bentonite swelling and erosion.

An approach is proposed for simulating the coupled processes of swelling and mechanical erosion of compacted MX-80 bentonites. The loss of mass at the water–soil interface is described by means of a simplified erosion model, assuming the “instantaneous” activation of erosion. A double-porosity formulation was adopted based on the Barcelona Expansive Model to describe the deformability of the bentonite. In addition, a state surface was introduced to describe the increase in macrostructural porosity caused by the swelling and destructuration of the aggregates. This formulation was implemented in the multiphysics partial differential equation solver Comsol Multiphysics (CM), which was adapted to incorporate a mixed method and a Lagrangian formulation. The “Deformed Geometry” module of the CM solver allowed for the smooth and continuous updating of the active material domain to the bentonite mass loss defined in the erosion model.Satisfactory data fits were obtained by simulating a variety of pinhole tests on MX-80 samples of various configurations. Thus, although more experimental validation is needed, and the approach could be further improved (introducing, e.g., the effect of water salinity), the obtained results indicate that this method is a useful starting point for describing and quantifying the coupled erosion and swelling of MX-80 bentonites.