An active drainage method for groundwater environment protection and tunnel safety control

The construction of tunnels in ecologically sensitive regions often seriously disturbs the balance of groundwater seepage fields. To control the stability of groundwater environment and consider the safety of tunnel structure, an active drainage method is proposed. Based on the Kexuecheng Tunnel in the mountainous city of Chongqing, China, theoretical calculations, numerical simulations and in-situ monitoring are applied to study the influence of the active drainage method on seepage and stress fields of small interval tunnels. The characteristics of tunnel groundwater discharge and water pressure under different drainage valve pressures and rainfall intensities are revealed, and the mechanical performance and safety factors of the tunnel lining are analyzed. The results indicate that the maximum shear stress and maximum tensile stress of the lining are located at the arch foot and bottom respectively, and increase with increasing groundwater level. Reducing the pressure of the drainage valve can increase the safety factor of the lining structure when excessive water pressure threatens the safety of tunnel structures. When the groundwater level drops too much, increasing the pressure of the drainage valve appropriately can reduce groundwater loss and help maintain the balance of the groundwater environment. In addition, the water pressure difference between the vault and bottom, as well as the water pressure asymmetry coefficient on the two sides of the tunnel, decrease with the increase of drainage valve pressure. Considering the tunnel water inflow, groundwater level change, water pressure and safety factors of lining, suitable drainage valve pressures are proposed for different rainfall intensities. An active drainage control system for tunnels in water-rich environment has been developed and applied, which can effectively achieve the dynamic balance between the groundwater level, water inflow and tunnel structural safety.