Dissolution of randomly distributed soluble grains: post-dissolution k0-loading and shear

Abstract

Sediments experience mineral dissolution in most natural settings, and as a result of engineered processes such as carbon dioxide injection. The consequences of mineral dissolution are studied using the three-dimensional discrete-element method by gradually dissolving randomly distributed soluble grains in a laterally constrained cell under constant vertical stress. Either additional vertical load under zero lateral strain or shear loading are applied after dissolution. Results show that dissolution is accompanied by global horizontal stress change, increase in vertical displacement and porosity, and decrease in coordination number. Post-dissolution, sediments are more compressible; shear loading encounters a diminished peak strength and reduced dilative tendency in sediments that experienced dissolution; however, all specimens evolve towards a common ‘critical state' strength and sediment fabric at a large strain (in the absence of reprecipitation, changes in grain shape, or changes in grain size distribution). The analysis of micromechanical parameters shows that the total number of contacts decreases during dissolution and remaining contacts carry higher forces. Higher granular interlocking hinders settlement and leads to the development of higher fabric and force anisotropy during dissolution. Granular arching effectively resists vertical displacement around dissolving grains, a honeycomb fabric emerges and the specimen gains a higher porosity during dissolution. Overall, the extent of dissolution (soluble fraction) and the level of particle interlocking/angularity define the evolution of micro- and macro-scale parameters during dissolution and its response to subsequent loading.