On the significance of interparticle friction to the mechanical behaviour of clay

¹ Geotechnical Engineering Department, Technology Research Institute, Technology Division, Obayashi Corporation, Tokyo, Japan
² Department of Civil and Environmental Engineering, Imperial College London, London, UK
³ Department of Physics, Imperial College London, London, UK
⁴ Department of Materials, Imperial College London, London, UK

^* Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Abstract

This study investigates the influence of interparticle friction on the one-dimensional (1D) compression behaviour of normally consolidated clay using coarse-grained molecular dynamics (CGMD). CGMD is a particle-scale simulation method where individual clay particles are modelled as flat ellipsoids, and the interactions between particles are described by considering the potential energy of the interaction. This potential energy depends on the distance between clay platelets. In the case of kaolinite DLVO theory can be used to predict this energy. Most potential energy functions that have been used in particle-scale simulations do not explicitly include interparticle friction, and so their predictions of key geotechnical behaviour are unreliable. This study uses a potential energy function that models interparticle tangential forces with a spring-slider (Coulomb) friction model. 1D compression simulations were then conducted on virtual samples of kaolinite assuming pore water pH values of 4 and 8, giving flocculated and dispersed microfabrics, respectively. We show that if interparticle friction is omitted in 1D compression simulations the resulting lateral earth pressure coefficients are unrealistic (i.e. K₀=1.0), and that including friction gives more physically accurate K₀ values (i.e. K₀ <1.0). Unloading-reloading simulations revealed that interparticle friction is essential to reproduce the hysteretic behaviour which can be experimentally observed in consolidation tests. These findings underscore the importance of incorporating interparticle friction in particle-scale simulations of clay and highlight the need to better understand friction on clay particle surfaces in geomechanics.