Coupled chemo-mechanics of intergranular contact: Toward a three-scale model

Mineral dissolution in the vicinity of a stressed grain contact undergoing irreversible damage strain is studied numerically at three scales: of a grain, grain assembly and macroscopic continuum. Rigid chemo-plasticity is used to simulate the phenomena in the solid phase at the micro-scale, coupled with the reactive-diffusion transport of the dissolved mineral across the grain. Dilatancy resulting from the material damage generates new free surface area around the asperity, in turn enhancing dissolution and material weakening. Extended Johnson approximation of the near-contact field is adopted. Upscaled variables at meso-scale simulate the stiffening of the grain system as a result of the subsequent mineral precipitation. The consequent redistribution of mass within the pore space, affecting soil porosity and stiffness is derived on macro-scale from the averaged micro-scale variables. Partial masses of the same mineral are shown to play different roles at macro-scale, which requires linking them to different processes (dissolution and precipitation) derivable only at a micro-scale. Cross-scale transfer formulation is investigated. The study applies to many processes of fluid–solid interdependence in soil mechanics, such as structuration and aging of natural soils, compaction and pressure solution of oil or gas bearing sediments.