Influence of mineral dissolution on the mechanical behaviour of a granular assembly under complex stress states

Rock and soil are natural assemblies of mineral grains. Dissolution of mineral compositions in a granular assembly can dramatically disturb and change the microstructure. Once the soil fabric and inter-particle contacts change, large deformations can develop and the shear strength can decrease. Currently there is a lack of understanding and experimental evidence of geomaterial behaviour subjected to mineral dissolution under realistic complex stress conditions. In this experimental study, extensive laboratory tests were conducted to investigate changes in the stress-strain relation, shear strength and critical state of a granular assembly after experiencing a substantial loss of particles by salt dissolution. During the salt dissolution process, a larger shear stress or confining pressure leads to a smaller increase of void ratio, a smaller positive state parameter, and a weaker strain-hardening behaviour. After the salt dissolution, the material grading becomes narrower, the grading state index decreases and the specific void ratio increases, leading to an upward shift of the critical state line. However, the increase of void ratio is more than the upward shift of the critical state line, thus the stress state changes from the dense side to the loose side, accompanied by a change of shearing behaviour from strain-softening to strain-hardening. Nevertheless, as the critical friction angle is dominated by the inter-particle contacts among coarse particles, with almost no change in the coarse content of the post-dissolution materials, only a slight decrease of 2.3° in the critical friction angle is found.