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Given rock mass joints filled with montmorillonitic clayey soils at various porosities and saturated by a monovalent electrolyte, we investigate the microscale responses of the clayey joints to different background salt concentrations. As analytical solutions are not possible for realistic arrangements of particles within the joints, we employ rather sophisticated micromechanical models based on the solution of the Poisson–Nernst–Planck equations by means of finite element methods, to estimate counter-ion and electrical potential distributions for different particle configurations. We then calculate the disjoining pressures using the van’t Hoff relation and Maxwell stress tensor. As the distance between the clay particles decreases and double-layers overlap, the concentration of counter-ions in the micropores between clay particles increases, pushing apart both faces of the rock joints. Because of this swelling pressure, particles need not contact one another in order to carry ‘effective stress’ throughout the system. This work may lead towards theoretical predictions of the macroscopic deformation of clay-filled rock joints based on the micromechanical modelling of particles found on the interfaces.
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