Numerical Investigation of Water Inflow and Seepage Characteristics in a Tunnel crossing Two Overlapped Parallel Faults

Abstract Water inflow is one of the main geohazards that threaten the safety of tunnels and other underground projects. Faulted zone is one of the important geological triggers for such events. Numerical investigations on the evolution of flow behavior in tunnels across fault zones are of significance to the predication and prevention of this type of geohazards. In this work, a numerical investigation model with two overlapped parallel faults is established according to the "Three Zones" fault structure theory. The rapid turbulent flow in the fault fractured zone and fault center core is simulated by using the improved Darcy-Brinkman (IDB) seepage model, while the slow laminar flow in ordinary rock zone is described by Darcy equation. The effect of relative position and distance between the tunnel surface and two overlapped parallel faults to the evolutions of pore pressure( P ), flow velocity( V ), and water inflow rate( Q ) around the tunnel excavation surface is studied through several scenarios. Our Numerical investigation results reveals that while the tunnel face is excavated into the fault center core, the fractured zone, the ordinary rock zone, and the center of the overlapped faults, the pore pressure value ahead of the excavation face increases while the flow velocity decreases sequentially. The inflow rate is the largest while the tunnel face is excavated to center of the fault center core and is the lowest in the ordinary rock zone. Moreover, the inflow rate is closely related to the range of the overlapped area between the two parallel faults. The investigation results offer a helpful reference to predicting early warning of water inflow geohazard when a tunnel cross two overlapped parallel faults.