Stress-induced ramiform karstic conduits along a bedding plane: insights from a coupled hydro-mechanical-chemical (HMC) model

Bedding plane partitions are an important geological medium to guide cave passages during the early stages of karstification in limestone formations. However, how stress load affects karst genesis processes along the large rough fractures remains poorly understood. Here, we develop a novel coupled hydro-mechanical-chemical (HMC) model to improve the understanding of this complicated process. This model considers a two-way mechanical-chemical coupling where dissolution perturbs the contact-stress distribution, in return impacting the fracture dissolutional enlargement. A non-linear correlation between the local fracture stiffness and contact stress is further incorporated. We study a two-dimensional horizontal fracture surface embedded in a three-dimensional rock block subjected to vertical stress loading. Simulation results show that dissolution causes local stress reduction (mechanical weakening), simultaneously accompanied by stress concentration at its fringe. The competition between dissolution-induced aperture enlargement and compaction-induced closure significantly retards the dissolution evolution. Without mechanical effect, linear dissolution fingering exhibits. As the applied stress increases, the secondary karstic conduits become more pronounced and a ramiform dissolution fingering featuring branching and winding is induced. Our results also provide important implications for understanding other engineering applications such as geothermal development and carbonate acidification.