Field Measurement Study on Deformation Characteristics of a Metro Station Induced by Deep Large-Scale Foundation Pits on Both Sides

Excavation of deep large-scale foundation pits in soft soil areas can induce adverse deformation of adjacent metro stations and even jeopardize their structural safety. Based on a typical case in Tianjin, where deep large-scale foundation pits were synchronously excavated on both sides of a metro station, field measurement data of station structural deformation during excavation were analyzed. Combined with two similar cases, the characteristics and patterns of station structural deformation induced by the entire excavation process of deep large-scale foundation pits on both sides in soft soil areas are summarized. The results show that the heave of the metro station structure caused by excavations on both sides in soft soil areas increases nonlinearly with excavation depth. The heave rate is relatively low in the early stage and increases significantly (by a factor of 2 to 3) when the excavation depth exceeds 10–12 m. Moreover, the heave induced during the deep soil excavation stage accounts for more than 40% of the total heave. Equal excavation depths on both sides help maintain uniform heave of the station structure; otherwise, greater heave occurs on the side adjacent to the deeper pit, resulting in a certain tilting deformation of the station. Asymmetric excavations on both sides cause the intermediate station structure to displace laterally toward the larger or deeper pit. A comparison of the three cases further reveals that lateral displacement is small when the station base slab is embedded far deeper than the excavation, but increases significantly when the two depths are comparable. Building on this, the effect of surcharge loading on top of the station on controlling structural heave is further discussed. Furthermore, corresponding engineering recommendations are proposed based on the deformation characteristics and patterns of the station structure.