Model test study on the mechanical response of metro tunnel to land subsidence

Land subsidence is a prominent engineering geological problem faced by many cities in the world and poses a serious threat to urban infrastructures. Xi'an is one of the cities in China that has suffered the most serious land subsidence disasters and has thus faced the challenges in its ongoing metro construction. To solve this problem, in this paper we carried out a model test and numerical simulation of metro tunnel that crosses a land subsidence area and analyzed the mechanical response of the tunnel and the deformation and failure characteristics of the lining. The results show that the tunnel exhibits downward flexural deformation in the middle, slight warpage on both ends in the longitudinal direction, and local torsion in the horizontal direction in the presence of land subsidence, the maximum deformation of the ground surface is about 80% of the tunnel deformation. Furthermore, the vault and inverted arch are in opposite tension–compression states, and the lining stress decreases inside the subsidence area but increases outside it. When the actual subsidence reaches 225 cm, the metro tunnel crossing the edge of the land subsidence area has failed. We find that the deformation and failure of metro tunnel crossing land subsidence area is a combination mode of flexural tension–compression and local torsion, which affects 2.5 times the length of the intersection between the tunnel and the subsidence area. Also, some countermeasures and suggestions are proposed to deal with the adverse impacts of land subsidence on metro tunnels.