Large-scale model test for studying the water inrush during tunnel excavation in fault

Water-rich fault fracture zone is one of the main factors leading to water and mud inrush in tunnels, which has attracted wide attention of scholars. In order to investigate the fracture and water inrush mechanism of fault surrounding rock under the disturbance of tunnel excavation and water pressure, taking Qilian Mountain Tunnel as engineering background, the fracture of fault surrounding rock caused by tunnel excavation is studied based on the self-developed model test apparatus. The model test system was comprised of a water supply system, acrylic glass holding device, and collection system. The experiment smoothly and successfully reproduced the process of water inrush in front of the tunnel face caused by excavation unloading and water pressure, and the deforming performance and stress distribution of surrounding rock were investigated. According to the experimental phenomena and data analysis, the process of water inrush could be divided into three stages. In the first stage, the tunnel face changed from dry to wet with the tunnel excavation, and the water pressure, soil pressure, and displacement of monitoring points were nearly unchanged. In the second stage, the water seepage area spread to the whole tunnel face from the bottom, and finally water inrush occurred. And the water pressure and soil pressure of monitoring points were increased significantly. At the moment of water inrush, the displacement of monitoring point in fault increased instantaneously; the water-resistant strata have obvious instability characteristics. In the third stage, the water inflow and sand inflow become fewer and fewer over time. And the seepage pressure and soil pressure of monitoring points on the right side of the tunnel decrease firstly and then increase, while the seepage pressure and soil pressure of monitoring points on the left side of the tunnel decrease sharply. The results provide a valuable reference for the mechanism research of water inrush.