Localized dissolution in sediments under stress

Abstract

Mineral dissolution and subsurface volume contraction can result from various natural and engineered subsurface processes. This study explores localized granular dissolution in sediments under constant vertical stress and zero lateral boundaries using 2D and 3D discrete element simulations to gather macro-scale and particle-scale information during dissolution. Local arches form when the dissolving inclusion size is similar to the grain size; however, granular chains buckle and grains flow to refill voids when dissolving inclusions are larger than the length scale of force chains (about 6-to-10 grain diameters). Force chains arch around the region that undergoes grain dissolution; interparticle contact forces are low within the contracting zone, yet are sufficient to provide transverse support to the major force chains. Higher granular interlocking leads to the formation of more pronounced force arches, results in higher internal porosity, and limits the vertical contraction. The vertical contraction and the global porosity increase proportionally to the lost solid volume, but remain below the upper bounds computed for dissolution at either constant internal porosity or constant global volume. The sediment porosity evolves towards a terminal porosity that is defined by granular interlocking; the minimum mass loss required to reach the terminal porosity can exceed 10-to-15%. The global stress ratio K0 decreases during the early state of dissolution and in sediments with high interlocking; otherwise, it evolves towards a steady value that can be as high as K0\u2009≈\u20090.7 to 0.8; this stress ratio is compatible with the horizontal reaction required to stabilize the internal force arches.