Failure mechanism of deep-buried and large cross-section subway station tunnel: Geo-mechanical model test and numerical investigation

In some megacities, urban subway and municipal engineering are developing in the tendency of large cross-section and great buried depth, which brings a series of challenges to the design and construction of underground engineering. The mechanical characteristics and failure mechanism of tunnels have been paid more and more attention. Based on Xietaizi Subway Station tunnel in Chongqing, China, the paper carried out a geo-mechanical model test to simulated partial excavation processes of the large cross-section tunnel, integrating the resultant disturbances from partial excavation. The deformation and stress characteristics of the tunnel under different buried depths are analyzed, and the failure mechanism of large cross-section tunnel lining is investigated. The reliability of the research results is verified by the geo-mechanical model test and numerical simulation. The results indicate that under the pressure of the surrounding rock, the tunnel lining adjusts its internal forces primarily through deformation before transitioning to cracking, and retains earing capacity after the first crack appears. The tunnel structure experiences a process characterized by ‘elasticity-plasticity-injury-failure’. The tunnel section exhibits a ‘flattening’ deformation trend. The invert cracks are primarily distributed within a range of 0.5 times the tunnel span, while the vault cracks are mainly concentrated at the mid-span. Ultimately, the tunnel structure is compromised by the fracture of the invert’s middle section.