## 3 Simulation Results and Analysis
### Discussion: Evolution Characteristics of Seepage Field under Different Water Pressures  
During the excavation of the tunnel approaching the rich-water fault, the change of water pressure inside the anti-inrush body is illustrated in Figure 5, where the numbers in different colors represent the water pressure. As can be observed from Figure 5, continued excavation does not lead to significant seepage through the face protective layer, suggesting that the excavation disturbance has a limited impact on the seepage stability of the face protective layer. As the tunnel advances and the distance between the tunnel working face and the water-bearing fault decreases, the influence of the excavation disturbance becomes more pronounced. When small-scale water inrush occurs at the lower part of the tunnel working face under the seepage pressure, this can be considered a precursor to the potential for sudden water inrush, with the face protective layer thickness approaching the minimum safe thickness. Eventually, the protective rock layer at the tunnel working face is unable to withstand the water pressure from the overlying fault, leading to an overall instability and failure. This results in a sudden change in the inrush flow rate, the formation of a stable sudden water inrush channel within the face protective layer, and a high-volume, high-pressure water inrush event. Furthermore, as shown in Figure 5, when the distance between the tunnel working face and the fracture zone of the water-bearing fault is the same, the maximum lateral extrusion displacement of the tunnel working face increases with the continuous rise in fault water pressure, indicating a higher susceptibility of the tunnel's protective system to sudden water inrush failure. Figure 4: Curve of displacement change of tunnel face center: (**a**) displacement varies with excavation steps; (**b**) displacement varies with water pressure. Figure 5: _Cont._To observe the evolution of the displacement field and seepage field of the face protective layer during tunnel excavation near a water-bearing fault, with water pressure changes as the object of study, 8 monitoring points were set up at the center and edges of the tunnel working face. This focuses on the water pressure changes at the monitoring point located at the center of the tunnel working face. Figure 6 illustrates the changes in water pressure during the excavation process of tunnel working face under different water pressure conditions, at the points with coordinates (6, 0, 0), (7, 0, 0), and (8, 0, 0), corresponding to curves 10, 11, and 12, respectively. Figure 5: Characteristics of the seepage field of the surrounding rock when the tunnel is approaching to fault with different water pressures (Unit: Pa): (**a**) \(p\) = 1 MPa, fourth excavation; (**b**) \(p\) = 1 MPa, fifth excavation; (**c**) \(p\) = 1 MPa, sixth excavation; (**d**) \(p\) = 1.5 MPa, fourth excavation; (**e**) \(p\) = 1.5 MPa, fifth excavation; (**f**) \(p\) = 1.5 MPa, sixth excavation; (**g**) \(p\) = 2 MPa, fourth excavation; (**h**) \(p\) = 2 MPa, fifth excavation; (**i**) \(p\) = 2 MPa, sixth excavation; (**j**) \(p\) = 2.5 MPa, third excavation; (**k**) \(p\) = 2.5 MPa, fourth excavation; (**l**) \(p\) = 2.5 MPa, fifth excavation. Figure 6: Water pressure change curve: (**a**) \(p\) = 1 MPa; (**b**) \(p\) = 1.5 MPa; (**c**) \(p\) = 2 MPa; (**d**) \(p\) = 2.5 MPa. As shown in Figure 6, under different fault water pressures, the changing trend of water pressure at the same monitoring point during tunnel working face excavation is essentially the same. Prior to any failure, the water pressure first exhibits an increasing trend, and then suddenly decreases after reaching a relatively stable state. The model calculation shows that up to approximately 20,000 steps, the face protective layer is minimally affected by water pressure, remaining in a relatively stable state. However, at around 27,000 steps, fault water seeps through cracks and enters the face protective layer.