Analysis of ultra-deep five-level underground station excavation in soft soil and its impact on existing structures

The deformation of adjacent existing structures induced by ultra-deep excavation in soft soil regions is a key technical challenge in urban underground space development. This study is based on an excavation of transfer station of Tianjin Metro Line 8, with a maximum depth of 38.3 m. A three-dimensional finite element model was established and validated against field measurement data, followed by systematic parametric analyses. The results reveal that adjacent buildings significantly amplify excavation-induced ground deformation, while the location of maximum settlement exhibits a regular migration trend with varying building distances. The existing underground station exhibits a pronounced shielding effect, effectively reducing excavation-induced ground settlement and diaphragm wall lateral displacement. The station undergoes torsional deformation towards the excavation, and its floor slab exhibits a characteristic "M"-shaped uplift pattern. The spacing between the station and the excavation is identified as the dominant factor controlling the shielding effect, whereas the influence of station burial depth is relatively minor. Increasing the burial depth tends to amplify lateral displacement of the side wall, whereas increasing the station-excavation spacing effectively reduces such displacement. The findings provide a quantitative theoretical basis for the design and construction of ultra-deep excavations adjacent to existing structures in soft soil regions.