Coarse-grained molecular dynamics simulations of clay compression

Abstract

This paper outlines a framework for using molecular dynamics to simulate the compression of kaolinite saturated at alkaline pH (=8) in a low (1 mM) concentration solution. The particles are modelled as flat (3D) ellipsoids and their interactions are described by a modified form of the Gay-Berne potential, calibrated against DLVO theory. The LAMMPS software was used to generate monodisperse and slightly polydisperse samples, and to simulate isotropic compression to 100 kPa. The influences of sample size and strain rate on the void ratio and the arrangement of particles within the samples were investigated via parametric studies. It is useful to consider the extent to which the system temperature (a measure of the average kinetic energy) is controlled when assessing whether the applied strain rate is appropriate. It is found that the number of particles that can be considered a representative element volume is orders of magnitude larger than the number simulated in earlier studies and that larger number of particles are required in polydisperse samples than in the monodisperse case. A comparison between the results obtained and those of published experimental studies show that the methodology proposed can deliver sensible results for the material considered.