Numerical simulation of water inrush in a tunnel crossing faults: impacts of fault width, damage zone width, and fault permeability

The reliable numerical model helps understand the water inrush mechanism in tunnels crossing faults. This paper established the numerical model based on the “Three Zones” fault structure, consisting of the fault core, the damage zone, and the host rock. The nonlinear water inrush process is simulated by solving the Darcy–Brinkman flow equation for host rock and fault zone. The impacts of the fault width, the damage zone width, and the fault permeability are analyzed on the pore pressure and flow velocity near the tunnel face. When the permeability varies, the pore pressure in front of the tunnel face decreases with increasing permeability, while both flow velocity and water inrush rate increase with increasing permeability. When the fault width is different, the larger the fault width, the larger the pore pressure and the water inrush rate within the range of 10–20 m in front of the tunnel face. The minimum water inrush rate corresponds to the case with a fault width of 1 m. When the width of the damage zone is changed, within 6.5 m ahead of the tunnel face, pore pressure and water inrush rate both increase with increasing damage zone width. In the range of 6.5 to 25 m ahead of the tunnel face, the larger the width of the damage zone, the lower the increasing rate of pore pressure. Furthermore, the flow velocity and the water inrush rate both increase with increasing the width of the damage zone. The results are of great significance for understanding the evolution process of water inrush when crossing fault zones and provide a valuable reference for predicting water inflow.