Participants:
T. Hueckel, L.B. Hu - Duke University
G. Cassiani, University of Padua, Italy
Subsidence of the ground surface as a result of water or oil pumping may reach tens of yards (meters) and cause major trouble to inhabitants or underground infrastructure. The photos above show a bridge in Italy around which the ground subsided more than a meter and a electricity pole in California on which historical levels of ground surface are marked.
Subsidence can be linked to the basic phenomena that occur at intergranular contacts over a long term which involve chemical process of particle dissolution under pressure. We studied mineral dissolution in the vicinity of a stressed grain contact undergoing irreversible damage strain at three scales: that of a grain, grain assembly and macroscopic continuum. Rigid chemo-plasticity is used in this study 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. We adopted extended Johnson approximation of the near-contact field. 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 can be derived on macro-scale from the averaged micro-scale variables. Partial masses 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 was also 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.
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Damage and mineral dissolution near an intergranular contact stressed in water for two weeks |
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Grain-indenter contact area after a two-week stressed contact in water, Visible are dissolution craters, intense in a dilated range near contact, gas bubbles, and damage intensity much higher than in a dry experiment |
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Volumetric dilatancy/damage distribution around the contact, together with mass loss density: simulation with a coupled chemo-plasticity model |