Impact of fault fracture zones on the seepage field distribution and groundwater discharge of tunnels

To investigate the impact of fault fracture zones on the seepage field distribution and groundwater discharge of tunnels, three-dimensional numerical models with different distribution patterns of fault permeability coefficient are established. These models reveal the varying characteristics of groundwater head, water pressure and water inflow as the tunnel traversed faults or their adjacent areas. By combining on-site measurement and synthetic conceptualizations of three cases, the distribution of seepage field and water inrush control measures of the Paoma Tunnel passing through multiple faults are studied. In the case of tunnel crossing a single fault, the water head values of the overlying and underlying strata significantly decrease once the fault is revealed during tunnel excavation. Transitioning from a C-shaped to L-shaped or U-shaped distribution pattern of fault permeability coefficient enhances the fault's impact on groundwater head distribution. In the case of tunnel near fault, increasing tunnel-fault distance results in lower permeability around the tunnel and steeper hydraulic gradient. The existence of fault causes asymmetrical distribution of hydraulic head, water pressure, and water inflow in the tunnel site. The case of tunnel crossing multiple faults mirrors the real conditions encountered in the Paoma Tunnel. Simulation results show the maximum water pressure and groundwater discharge within fault zones are 10 ~ 30 times higher than those in the non-fault section. After grouting reinforcement of the fault fracture zone, the groundwater head and water pressure significantly increases, and the maximum water inflow decreases by nearly 90% compared to the non-grouted state.