Impact of Water Gushing Influenced by the Relationship between Fault and Tunnel Position

In order to analyze the influence of the position relationship between the fault and the tunnel on the water inrush, the fault is regarded as a constant head boundary, the bounded aquifer is transformed into an unbounded problem by the reflection method, and a simplified calculation model of the tunnel water inrush is constructed. Based on the theory of groundwater mechanics, Darcy’s law, and the linear superposition principle, the calculation expressions of water inflow and structural external water pressure are derived, and degradation analysis is performed. The correctness of the model is verified by numerical simulation and field test data. Afterward, the sensitivity of the characteristic parameters is studied, and the influence mechanism of the grouting structure and faults on the tunnel water gushing is discussed. The research results show that in order to ensure the safety of the secondary support structure of the tunnel, appropriate grouting circle thickness and a permeability coefficient should be set, and the permeability coefficient of the secondary support structure should be appropriately increased. When the seepage is stable, the tunnel water inflow will increase nonlinearly with the increase of the fault dip, and the sensitivity will gradually increase; when the fault dip is fixed, with the increase of the distance from the tunnel, the restriction of the fault on the tunnel is weakened, and the water inflow decreases continuously. In the case project, the theoretical and measured water inflows of the unfaulted section, single-faulted section, and combined-faulted section differ by 13.36%, 12.79%, and 10.85%, respectively. The difference between the theoretical value and the measured value of the outer edge water head height of the secondary support structure was 10.7%, 10.51%, and 13.87%, respectively. The research results can provide a theoretical basis for the calculation and structural design of tunnels in water-rich fault areas.