Deformation characteristics and failure evolution process of the existing metro station under unilateral deep excavation

With the rapid development of underground space construction, there are more and more large-scale deep foundation pit projects on one side of the metro station. Unilateral deep excavation will result in an imbalance of the earth pressure on both sides of the existing metro station, which is a major engineering risk. Therefore, considering the station width and the excavation depth, this study focuses on the deformation characteristics and failure evolution process of the existing metro station structure caused by unilateral excavation based on the physical model test and discrete element method (DEM) analysis. This research shows that the lateral deformation of the top of the station caused by unilateral excavation is the most significant. Secondly, as the excavation depth increases and the station width decreases, the increase rate of the station overall inclination and lateral displacement becomes more significant. Thirdly, the structure fails when the excavation depth is 5/6H (H is the station height). Then the station instability leads to three disturbed regions in the adjacent stratum. The contact force between soil particles in the disturbed region is small and the stability is poor. Finally, the failure evolution process of the existing station under unilateral excavation is divided into three stages: (a) when the excavation depth is 0–1/2H, the soil and structure are stable; (b) when the excavation depth is 1/2–3/4H, the lateral deformation and inclination of the station reach the security warning range; (c) when the excavation depth is 3/4–1.0H, the structure is unstable and slips laterally, resulting in the ground collapse and local soil extrusion failure. This study reveals the risks of the existing station at different excavation stages, which can make risk prediction for the construction of the project.