Pressure-dependent grain dissolution using discrete element simulations

摘要

Pressure solution-precipitation is a diagenetic process often involved in compaction, hardening, creep and healing. This study explores the evolution of pressure-dependent mineral dissolution using the discrete element method where grains are gradually contracted in proportion to the total normal force they carry. Under zero lateral strain and constant vertical stress boundary conditions, contact forces homogenize during the early stages of dissolution, there is a minor increase in coordination number and the global porosity decreases (even though there is no reprecipitation in these simulations). There is a transient drop in the lateral stress, shear bands start to emerge as the horizontal stress reaches a minimum value. The porosity is higher and the coordination number is lower within shear bands than in the surrounding soil wedges; furthermore, interparticle forces tend to homogenize within wedges, while marked force chains develop within shear bands. On the other hand, there is no shear localization during pressure solution simulations under isotropic stress boundary conditions. Regardless of the boundary conditions, the initially uniform grain size distribution evolves towards a unimodal distribution; improved particle grading facilitates the global reduction in porosity and the associated increase in coordination number. The emergence of shear discontinuities during pressure solution under zero lateral strains may explain the non-tectonic origin of polygonal fault systems observed in marine sediments and lacustrine deposits.