Experimental Investigation of Progressive Failure Characteristics and Permeability Evolution of Limestone: Implications for Water Inrush

Water inrush represents a significant hazard in karst tunnels, and the water-resistant rock mass plays a pivotal role in water inrush incidents. It is of great significance to explore the coupled hydro-mechanical failure process of water-resistant rock mass under excavation. A series of triaxial compression tests with different pressure conditions and loading rates were conducted in this study to investigate progressive failure characteristics and permeability evolution of limestone specimens. The experimental findings demonstrate that loading rate and confining pressure significantly influence progressive failure characteristics and permeability evolution. Additionally, a decreasing-then-increasing trend is observed in the crack initiation threshold (σci), and the crack damage threshold (σcd) exhibits a decreasing tendency. The resulting σci/σp ratio increases while the σcd/σp ratio decreases, indicating a diminishing stable fracture development stage. In general, permeability experiences an increase within an order of magnitude during the progressive failure of rock specimens, and the permeability of the rock mass decreases with rising initial confining pressure. The rate of deformation induced over the duration of permeability measurement exhibits a positive correlation with the stress ratio. Lastly, we propose a potential hysteresis water inrush mechanism, drawing upon the aforementioned observations. It is deduced that the creation, expansion, and ultimate penetration of fractures within the rock mass, resulting from the combined effects of excavation stress disturbance and changed pore pressure, give rise to water inrush events in karst tunnels.