## 2 Tunnel Description and Geological Conditions
### Establishment of the DEM-Based Computational Model
#### 3.3.2 Change Rule of Seepage Pressure Field  
During the excavation of the fault-crossing tunnel, the evolution of the seepage pressure field of the water-resistant rock mass at the face is displayed in Figure 6. Figure 6a demonstrated that after the completion of the second excavation step, the fault water entered the fissure connecting the water-resistant rock mass and the fault fracture zone, but the seepage effect of the face was not obvious at this time. It could be observed from Figure 6b,c that the seepage effect was increasingly obvious, and the closer the face to the fault, the faster the water pressure increased. Figure 6d confirmed that after the completion of the fifth excavation step, the water-resistant rock mass at the face was destabilized and damaged under the seepage. For each excavation of the tunnel, eight monitoring points were set up on the excavation surface to monitor the change in water pressure. Since the displacement response at the center of the face was more pronounced than that at the edges during the excavation, the change in water pressure at the center of the face was analyzed. The change curves of water pressure at measuring points (6,0,0), (7,0,0), and (8,0,0) are displayed in Figure 7.  
Figure 6: Evolution law of seepage field (unit: Pa): (**a**) Second excavation (\(h\) = 10 m); (**b**) Third excavation (\(h\) = 8 m); (**c**) Fourth excavation (\(h\) = 6 m); (**d**) Fifth excavation (\(h\) = 5 m).  
Figure 7 showed that the water pressure of the fault at measuring point (8,0,0) was constant at 2 MPa. With the continuous excavation of the tunnel, the water pressures at measuring points (6,0,0) and (7,0,0) followed the same trend before the damage of the water-resistant rock mass. As the face gradually approached the fault, the water in the fault continuously entered the fissure, resulting in the rising water pressure. When the water-resistant rock mass at the face of the tunnel was damaged, the fissure was connected to the face, which led to the water flowing out from the face and the sudden decrease in fissure water pressure. The water-resistant rock mass underwent a large deformation under the joint action of disturbance stress and water pressure, and the blocks in the model were squeezed or separated from each other, resulting in a sharp change in the fissure width.  
The variation in water pressure at each measuring point indicated that water in the fault flowed into the fissure at the early stage of tunnel excavation, and water pressure in the fissures increased continuously. Once the excavation face intersected the pre-established fissures, the water in the fissures flowed out from the face under the influence of the excavation disturbance, and the water pressure decreased. Then, the water pressure continued to rise under the recharge of fault water. When water intrusion damage of the water-resistant rock mass occurred, the water pressure at each measuring point near the damage area increased sharply.  
Prevention and Control Measures for Water Inrush at the Face of the Tunnel Adjacent to the Water-Rich Fault and Its Effectiveness  
Relevant countermeasures should be implemented to prevent the water inrush disasters of tunnels adjacent to fault fracture zones. Based on the engineering practice, the grouting reinforcement measure of water inrush and mud outburst in the 2# edit of Xianglushan tunnel was investigated, and the prevention and control effect was evaluated.