Numerical Analysis of the Blockage Effect of the Tunnel Drainage System on the E-Han Expressway

The discharge of groundwater and the load on the lining structure are both significantly impacted by the obstruction of the tunnel drainage system. In this study, the fluid-structure interaction model was established based on the finite difference software FLAC(3D). Then, this research explored the effects of symmetric and asymmetric blockage in the circular drainpipe, the transverse drainpipe and at the pipe joint in the tunnel on the pore water pressure, displacement and stress of surrounding rock. Our research revealed the following points: (1) When a symmetrical or asymmetrical blockage occurred in a circular drainpipe, only the blocked part of the drainpipe would be affected, but the pore water pressure at the back side of the tunnel crown and side wall lining between two adjacent circular drainpipes would increase by 200%, stress increase would increase by 22% and displacement would increase by 41%. (2) When a symmetrical or asymmetrical blockage occurred in a transverse drainpipe, the pore water pressure at the back side of the tunnel crown and side wall lining between two adjacent circular drainpipes increased by a maximum of 146%, the stress on the tunnel crown lining increased by a maximum of 4% and the tunnel crown lining was displaced by 8% to a maximum extent. (3) Both symmetrical and asymmetrical blockage of the tunnel drain joint led to the failures of the circular drainpipe and the transverse drainpipe connected with the tunnel drain joint. This increased the pore water pressure on the back side of the lining between the two adjacent drain sections and had an impact on the pore water pressure, stress and displacement of the surrounding rock nearby.