Modelling the swelling of a bentonite pellet using a triple porosity model

Abstract

In this work, the scope of a macroscopic triple porosity (mega-, macro- and micro-porosity) model is assessed by analysing its application in simulating the hydration and free swelling of single bentonite pellets. Flow is assumed to be concentrated in the megapores existing between the bentonite grains. Therefore, its application to the analysis of single pellets is very demanding, as the volume of these megapores is initially very small. However, the good results show the consistency of the formulation used to describe the flow, as this formulation accurately reproduces the hydration of the pellets. Swelling is also satisfactorily reproduced with a new mechanical formulation that addresses the rearrangement in megaporosity that the microstructure can cause under conditions of reduced confinement. Furthermore, this new formulation enables the model to provide a macroscopic description of the evolution of megapores that is consistent with results obtained through microscopic experimental techniques when analysing the cracking process experienced by the pellets. This result is especially notable because not only has it not been obtained previously by other macroscopic models, but it also provides significant confidence in the new proposed mechanical formulation, which retains simplicity by introducing a single additional parameter.