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

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.

Coarse-grained molecular dynamics simulations of clay compression

“…Due to its mathematical form, the GB potential cannot reproduce the attraction at short distances predicted by DLVO equations, arising when ℎ<ℎ ?" (Bandera et al, 2019). This does not present a problem during initial loading; rather, it must be solved to simulate unloading, and this is beyond the scope of the current study.…”

“…𝐸 56, is the Coulombic interaction between charged surfaces screened by ions in solution which partially neutralise them (Masiliyah and Bhattacharjee, 2006). 𝐸 56, can be either repulsive or attractive depending on the signs of the charges of the interacting surfaces (Bandera et al, 2019;Gupta, 2011;Gupta and Miller, 2010;Kumar et al, 2017;Liu, 2015): surfaces whose charges have the same sign repel and those with oppositely signed charges attract. While there are several expressions that relate 𝐸 56, to the separation of the two charged surfaces, an exact analytical solution does not exist.…”

Recent Advances in Nature-Inspired Solutions for Ground Engineering (NiSE)

“…Mesoscale models then inform micro-scale models, such as constitutive soil models, which are then extrapolated to engineering properties and capitalised for the benefit of geotechnical and petroleum engineering applications. The thermodynamic perturbation method is gaining interest at mesoscale [9,10]. Alongside with MD simulation, the two methods combined are offering a chance to study interactions of multiple platelets with varied orientation (Fig.…”