Performances of adjacent metro structures due to zoned excavation of a large-scale basement in soft ground

Abstract A field case of a large-scale basement excavation constructed at a side of a metro station was extensively reported and analysed. The 236.7-m-long, 145.8-m-wide, and 23.2–27.3-m-deep multistruted large excavation in soft clay was divided into six different size zones by five partition walls. A zoned-excavation procedure was adopted to minimize the excavation-induced adverse effects on the adjacent metro station and shield tunnels. A comprehensive program of instrumentation and full-time monitoring was conducted to measure the performances of excavation and responses of shield tunnels and metro station. The lateral wall deflections, ground surface settlements, vertical and horizontal displacement of shield tunnels and metro station and the tunnel convergences during the entire excavation were comprehensively monitored and analysed. This project provides an unusual opportunity to investigate the corresponding responses of metro station and shield-driven tunnels to each separated zone excavation. The measured results show that the diaphragm walls developed deep-seated movements towards excavation side during excavation procedure. Significant ground settlements behind the diaphragm walls were developed as excavation proceeded. Heave was observed in the tunnel tracks within the metro station, whereas shield-driven tunnels experienced large settlement during the excavation. Horizontal movements and elongated in shield tunnel were observed in the tunnel tracks along their longitudinal directions during the excavation-induced stress relief.