## 2 Overview of the Project  
The Gudou Mountain Tunnel is located at the southern end of the Yinzhou Lake Expressway in Jiangmen, Guangdong Province. The tunnel spans 3293 m, featuring a bi-directional, six-lane design with each tunnel having a width of 15.5 m, a height of 5 m, and a 32 m gap between the two tunnels. The gully in the tunnel area is wide and slightly semi-enclosed, and the surface streams are perennial, so there are many water conservancy facilities in the reservoir. According to the hydrogeological report, the main reservoirs associated with the Gudou Mountain Tunnel are the Yau Kam Hang and Song Chai Hang Reservoirs. The spatial relationship between the tunnel and these reservoirs is detailed in Figure 1.  
The engineering geological investigation of the Gudou Mountain Tunnel revealed that a fault crosses the tunnel at 20\({}^{\circ}\)/75\({}^{\circ}\). It intersects the tunnel at K51 + 610 m at an oblique angle of 61\({}^{\circ}\), impacting the section from K51 + 590 to K51 + 640 m. The fault zone primarily consists of crushed and fragmented rock. Figure 2 illustrates that the tunnel site's stratigraphic surface is of quaternary layers underlain by Yanshanian granites.  
The Gudou Mountain Tunnel is situated adjacent to a reservoir and traverses a fault fracture zone. Developed joints and fissures in the fault zones may facilitate deep water conduction and create water-rich spaces, enabling a hydraulic connection between the tunnel and the reservoir. Following the completion of initial tunnel support, water gushing occurred at multiple points in the vault, with seepage at the arch waist and significant water flow at the inverted arch, as depicted in Figure 3.  
During tunnel operation, increased rainy season precipitation raises both the groundwater level at the tunnel site and the reservoir water level. Considering water's erosive effects on strata, new seepage channels may form in the surrounding rock with nodal fissures in the faults likely becoming conduits between the tunnel and reservoir. The Gudou Mountain Tunnel's design specifications mandate regular monitoring of the tunnel lining's deformation during operation to prevent seepage and leakage and ensure safe tunnel operation.  
Using the K51 + 590-K51 + 640 tunnel section as a prototype, with steep mountains on either side conducive to rainfall accumulation, we examine the distribution of water pressure and deformation patterns in the tunnel lining across the fault zone during operation based on field test and numerical simulation. According to Chinese Highway Tunnel Design Standards, the quality levels of the peripheral and fault rock bodies in this section are classified as IV and V, respectively. Physical and mechanical parameters of the tunnel's surrounding and fault rock were derived from geological data and an indoor test of the Gudou Mountain Tunnel, as detailed in Table 1.  
Figure 1: Location of the tunnel in relation to the reservoir.  
Figure 2: The geological profile of the tunnel site area (K51 + 260–K52 + 060).  
The tunnel features anchoring and shotcrete support with a U-shaped lining design. Rock support for the tunnel vault and sidewalls consists of 22 mm diameter, 300 cm long resin bolts. Initial support is provided by 24 cm thick C25 shotcrete, which is reinforced with rock bolts, steel mesh, and steel arches. The secondary lining comprises 55 cm thick C30 concrete. Between the initial and secondary linings, a waterproof layer of EVA sheeting and non-woven fabric is installed, which is complemented by circular blind drains running longitudinally for drainage.