Evaluating the Deformation Performance of Long and Narrow Subway Foundation Pits and Their Effects on Adjacent Buildings: Insights from Numerical Modeling and On-Site Monitoring

Ensuring deformation control of deep excavations and the safety of adjacent structures is a paramount concern in urban underground construction. This study investigates the disturbance effects induced by the excavation of a long and narrow foundation pit on the surrounding environment, using the Chexie Road Station pit of Suzhou Rail Transit Line 8 as a case study. Comprehensive and usable geotechnical data were acquired through a series of laboratory and field tests, which served as the foundation for this research. Both numerical simulation (Midas GTS NX) and on-site monitoring were employed to analyze the responses of the ground surface, enclosure structure, and an adjacent operating metro station, as well as nearby buildings to the excavation unloading. The results indicate that the maximum ground surface settlement occurs near the midpoint of the pit’s long side, and the settlement trough is located approximately 10 to 15 m from the pit edge. The depth of the maximum lateral displacement of the diaphragm wall (Hm) is found to be within the range of (He−2) to (He+2), where He is the excavation depth. Furthermore, existing buildings situated adjacent to the middle of the foundation pit’s long side are most susceptible to excavation-induced disturbances, whereas the impact on the operating station near the end well is relatively minimal. Consequently, it is recommended that monitoring efforts be intensified in the central region of the foundation pit’s long side during construction to strictly control excavation-induced disturbances.