Study on the influence of groundwater table rebound on tunnel structure: A case study from Xiangshan tunnel

The surface pre-dewatering is usually carried out before the excavation of the tunnel within water-rich fine sand stratum. Due to the high cost of surface pre-dewatering, the area of the tunnel that has been applied for the first lining may not continue to pre-dewatering, and the groundwater level will rise again. Under the influence of rising groundwater level, the first lining of the tunnel may appear large deformation and cracking phenomenon. Taking Xiangshan Tunnel as an engineering case, the influence of groundwater level rise on tunnel supporting structure was was investigated. Firstly, the main engineering problems faced in the construction and the corresponding dewatering measures were reviewed. Then the deformation of surrounding rock, contact pressure, stress and groundwater level in the construction process were monitored and analyzed. The groundwater level rebound will cause large vertical settlement of the first lining and large extrusion deformation of the tunnel face. When the groundwater level reaches the arch waist, the minimum principal stress at the first lining arch foot exceeds its ultimate strength, and it will crack and fail. The increase of surrounding rock moisture content caused by groundwater rebound is the main reason leading to the failure of the first lining. Reducing the groundwater level, adding steel arch to the damaged section of the first lining and carrying out radial grouting can effectively solve the problem of first lining cracking. The experience and lessons learned in the construction process of Xiangshan can provide reference for similar projects in recent years.