Clay is the most commonly encountered geological material on the Earth’s surface and the engineering properties of soils are strongly affected by their clay content. Understanding and predicting the mechanical behaviour of clay (i.e. strength and compressibility) is then important to successfully deliver large scale infrastructure and building projects, to manage existing infrastructure, and to assess the hazard posed by natural clay slopes.
It is well known that processes occurring at the particle scale (i.e. microscale) significantly impact the response observed at the macroscale. While particle-scale simulations of sand behaviour are generally accepted as a research tool in soil mechanics, the use of particle-based modelling to simulate clay for geotechnical engineering applications is not well developed. This is attributed to the particulate nature of clay and to the chemical sensitivity of the particles’ interactions, which result in a highly complex behaviour.
This research work critically analyses the key decisions required to develop an effective framework for using Molecular Dynamics (MD) to perform particle-scale simulations of kaolinite and provides recommendations to facilitate other particle-scale studies of clay behaviour. The influence of pore fluid on the mechanical behaviour of kaolinite was assessed by simulating element tests saturated with a pore fluid with alkaline pH (=8) and acidic pH(=4) in a low (1 mM) concentration solution. Kaolinite particles are modelled as flat three-dimensional ellipsoids and their interactions are described by a modified form of the Gay-Berne potential, calibrated against energy-separation distance curves determined using the DLVO theory. The LAMMPS software was used to generate monodisperse and slightly polydisperse samples, and to simulate isotropic compression and one-dimensional compression to 100 kPa. Results at both macro- and micro-scale were analysed and 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.