Cause Analysis of High Pressure Water Gushing in Hongtu Extra-Long Tunnel

The Hongtu extra-long tunnel is the key control project of the Dafenghua Expressway crossing Lianhua Mountain in Guangdong Province. The maximum buried depth of the tunnel is 740 m. In the process of tunnel excavation, a large flow of water was encountered under the pressure of 4.8 MPa, and the maximum water volume is 1.4×10⁵ m³/d. By analyzing the influence of tunnel geological structure, the situation of high-pressure water inflow and its main water-conducting structure were expounded during the excavation process. At the same time, the water volume during the water inflow process was tracked, and the water quality of water inflow at different tunnel sections was compared. Three water storage structure modes, such as Tongziyang syncline water storage structure, rock mass intrusion contact water storage structure, and fracture fissure water storage structure, were proposed under the influence of the Lianhuashan fault in the Hongtu extra-long tunnel. Based on the relationship between the water inflow characteristics of the whole tunnel and the geological structure, it was proposed that the high-pressure water inflow mechanism of the tunnel was mainly affected by the horst-type hydrogeological model formed by the influence of the Lianhuashan fault, which makes the tunnel encounter high-pressure and large-flow water inflow during excavation. After penetration, it was controlled by the deep water storage cycle. After the stability of the groundwater system was rebuilt, nearly 60000 m³ large-flow water inflow per day is consistent with the actual situation.