Stress analysis of primary support arch cover excavation in metro station based on 3D geomechanical model experiment

Abstract

By considering a certain subway station of Qingdao Metro Line 1 as the research object, a 3D geomechanical model was established to analyze the stress and deformation characteristics of the surrounding rocks of a large-span subway underground station under primary support arch cover excavation. Fiber grating sensors, resistance strain gauges, earth pressure gauges, and multipoint displacement meters were arranged to monitor changes in stress and displacement of surrounding rock masses in the tunnel. The vault surrounding rock experiences excavation disturbance and rapid release stress, which consequently stabilizes. The excavation response of the arch foot to the monitoring section is gentler than the vault stress. Further, the horizontal stress of the sidewall sustains slow release, and the primary support stress increases rapidly, slows down, and finally stabilizes. The initial stress of the initial branch increases slightly after the first rapid growth, and the final trend is stable. During the process of advancing of the tunnel face, deformation undergoes three main stages, namely, slow, abrupt, and stable deformation, with continuing arch cover excavation. Although the surface subsidence is consistent with the vault subsidence, it has a lower value than the vault subsidence. The influence of the surface subsidence caused by excavation is larger than that of the vault subsidence, and the influence of axial subsidence on the tunnel is approximately 15 m. The primary support arch cover excavation can be successfully applied to large-span hard-rock metro stations whose surrounding rock grade is II–III; this provides a theoretical basis and reference for similar projects.