Experimental and numerical study of the water inrush mechanisms of underground tunnels due to the proximity of a water-filled karst cavern

The mechanism of lagging water inrush in underground tunnel constructions due to the proximity of a karst cavern with confined water is investigated via large-scale physical three-dimensional (3D) model testing and 3D numerical simulations. A new method is proposed for the preparation of modeled karst caverns filled with confined water. The physical 3D model testing is divided into two stages: tunnel excavation and hydraulic pressure loading. Multivariate information is obtained at the two stages using multiple measurement techniques. The results indicate that the displacement, hydraulic pressure, and the developmental trend of the damage zone in the tunnel excavation process are related. It is evident from the physical 3D model testing results that the process of water inrush can be divided into three stages, which include the initiation of group cracks, the formation of a water inrush channel, and the complete collapse of the water-resistant slab. The 3D model testing in conjunction with the 3D numerical simulations reveal that the disturbance due to excavation has an obvious impact on water inrush channel formation. However, an increasing hydraulic pressure in the karst cavern has a greater impact on the collapse of the water-resistant slab. These test results can provide support and guidance for tunnel construction under conditions that are susceptible to water inrush events.