Qinghan Li

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.

Ultra-deep excavations in soft soil pose major challenges for deformation control. Based on field monitoring of a 38.3 m deep five-story metro excavation in Tianjin, this study systematically investigates the spatiotemporal deformation of the diaphragm wall, columns, and surrounding environment. Key innovations include the proposal of an extended ground settlement influence model and the quantification of stage-wise deformation development ratios. The maximum lateral wall displacement is about 40 mm, ranging from 0.028% H_e to 0.184% H_e (average 0.087% H_e), outperforming comparable bottom-up excavations in Shanghai. Wall top vertical displacement varies from −0.23% H_emax to 0.04% H_emax, and column rebound averages 3.5 mm, is significantly lower than that of excavations using the bottom-up method. The extended settlement model shows that the maximum settlement occurs at H_e/3 from the wall, the primary influence zone extends to 3H_e, and the secondary zone reaches 5H_e. Building settlement strongly depends on distance and foundation type, with raft foundations settling much more than pile-raft foundations. Stage-by-stage analysis reveals that, immediately after the completion of diaphragm wall construction, the settlement already exceeded 60% of the final maximum ground settlement. Furthermore, the deformation on the long side developed at a faster rate than that on the short side. These findings provide quantitative benchmarks for designing ultra-deep excavations in soft soil.