Fully coupled hydromechanical study of tunnel excavation considering leachate leakage from a high water-level landfill

The Jigongshan Mountain Tunnel was constructed beneath a high water-level landfill in Shenzhen, China. Previous studies could not fully capture the hydraulic interactions between the tunnel excavation and the landfill leachate seepage. In this study, a fully coupled hydromechanical numerical model, considering the unsaturated properties and the changing permeability of the waste and geological materials, was established to simulate the landfill leakage and the tunnel excavation simultaneously. Parameter analysis was conducted to explore the effects of the configuration and dimensions of the leakage pathway and leakage points on the seepage field. Results indicate the landfill leakage has a minimal effect on tunnel displacement. The leakage width and the leakage path in the clay significantly affect the pore pressure of the tunnel. In scenarios of severe leakage, the pore pressure of the tunnel can reach as high as 0.615 MPa. Three defensive lines and the fully cover waterproofing layer were suggested for the tunnel waterproofing system under the Xiaping landfill. This research contributes valuable insights for the design and construction of subsurface structures in proximity to landfills.