An evaluation of contact models for particle-scale simulation of clay

Sara Bandera,Catherine O'Sullivan,Stefano Angioletti-Uberti,Paul Tangney,A Tarantino,E Ibraim

doi:10.1051/e3sconf/20199214001

Abstract

Geotechnical engineers are well aware that the particle surface chemistry and the pore fluid composition can significantly influence the mechanical behaviour of clay. Reference is often made to the Derjaguin-Landau-Vervey-Overbeek (DLVO) theory, which enables the electrochemical interactions between charged particles to be estimated. Hitherto, the absence of an effective framework for particle-scale simulation of clay has inhibited a direct link between these electrochemical interactions and clay behaviour (e.g. load:deformation response) or fabric (i.e. the development of a disperse or flocculated fabric). Ebrahimi [1] demonstrated the viability of using molecular dynamics simulations where the clay grains are simulated as ellipsoidal particles whose interactions are described by an analytical expression called the Gay-Berne (GB) potential. While promising when compared to other approaches documented in the literature, Ebrahimi's work considered only a single clay mineralogy and did not explicitly account for the pore fluid composition. This paper considers the use of the Gay-Berne potential in particle-scale modelling of clay from a more general perspective. Calibration of the GB model parameters to predict kaolinite particle interactions reveals a lack of generality in Ebrahimi's approach. The Gay-Berne potential cannot simulate situations in which attractive and repulsive interactions co-exist, which lead to the classical “cardhouse” fabric, as is the case of kaolinite particles interacting via an acidic pore fluid.

Highlights

Inter-particle forces between clay particles can be categorised as contact and non-contact forces (e.g. [2])
Particle-scale simulations have the potential to advance the understanding of clay behaviour
Recognising the computational benefits of this approach, this contribution has examined whether it can be applied to clays in general, i.e. it has extended consideration of the model beyond the montmorillonite particles considered previously and explicitly considers the pore-fluid chemistry

Summary

Introduction

Inter-particle forces between clay particles can be categorised as contact and non-contact forces (e.g. [2]). It is generally accepted in soil mechanics that the electrochemical forces can be described by the DLVO (Derjaguin-Landau-Vervey-Overbeek) model ([2], [5]) This model was developed in the 1950s to explain the equilibrium behaviour of colloids in solution and describes the variation of the potential energy of the particle-particle interaction with separation distance. Pagano et al [10] proposed a 2D DEM model with a simple tri-linear contact formulation that considers the DLVO forces in a highly ideal manner and simulates particle contact In each of these contributions, a single kaolinite clay particle was modelled as an assembly of spherical sub-particles clustered together to form a rigid body. The selection of the DLVO model parameters used here is discussed, prior to presenting a critical analysis of the ability of the GB potential to model kaolinite particles interacting through potassium chloride (KCl) solutions with a range of pH values

Modelling particle interactions

Kaolinite particle interactions

GB Model Calibration

Conclusions