Objective Soft soil strata generally exhibit unfavorable engineering properties, such as low strength, high moisture content, significant compressibility, and uneven stratum distribution, showing complex stress-deformation behaviors. These characteristics impose higher requirements on the prediction accuracy of excavation-induced deformation and construction control standards. Therefore, it is necessary to conduct in-depth research on the influence of deep foundation pit excavation for newly-built stations on both the foundation pit itself and the structural safety of adjacent existing metro station in operation.

Method Taking a newly-built station project of Suzhou Metro Line 8 as case study, the project overview is briefly introduced. Three types of monitoring points are arranged around the foundation pit. By organizing field monitoring results, displacement variation data for the ground surface around the foundation pit, retaining walls of the foundation pit, and side walls of the existing station are obtained. Numerical simulation methods are used to model and calculate four commonly adopted excavation sequence schemes and three excavation ranges in engineering practice, in order to determine the reasonable excavation sequence and excavation range for foundation pit earthwork.

Result & Conclusion  In soft soil areas, zoning phenomena of ground heave and settlement exist around the foundation pit, and the displacement variations change significantly across different zones. When the existing station is within the influence range of foundation pit excavation, its main structure gradually uplifts with the increase in excavation depth. The near-end side wall of the existing station inclines away from the foundation pit under the influence of excavation, forming a soil settlement zone between the new and existing stations. Compared with the near-to-far stepwise excavation method, the far-to-near stepwise excavation method reduces the maximum land subsidence by 5.08%, decreases the lateral displacement of the retaining wall by 4.57%, significantly improving the deformation condition of the existing station side wall. Reasonably reducing the amount of earth unloading in a single excavation stage or reducing the total number of excavation steps can somewhat optimize the influence of foundation pit excavation on surrounding soil and building structures.