MULTI SCALE APPROACH TO CHEMO-MECHANICAL COUPLING IN SOILS
Compaction of sediments and soils in the presence of chemical reactions of minerals: a three scale study
Tomasz Hueckel and Liang Bo Hu
Duke University
Mineral dissolution occurs with an enhanced intensity in the vicinity of a stressed grain contact undergoing irreversible damage strain. Its results affect sediment and soil behavior as a continuum, giving rise to evolution of their compressibility and permeability. The mechanisms of this evolution need to be considered at three scales: of a grain, grain assembly and macroscopic continuum.
In this project numerical simulation is performed of the mechanisms of evolution of sediments at three scales: the scale of a single grain, grain assembly and macroscopic continuum. At the micro-scale, rigid chemo-plasticity is used to simulate the phenomena in the solid phase, 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. At the meso-scale, upscaled variables 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 mass of the same mineral is shown to play a different role at macro-scale requiring to link 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 and sediment mechanics, such as structuration and aging of natural soils as well as compaction and pressure solution of oil or gas bearing sediments.