Deformation Characteristics and Control of Adjacent Building Piles Subjected to Multi-Pit Excavation in Highly Permeable Gravel Deposits

Waterfront multi-pit excavation in highly permeable gravel deposits can induce complex pile deformation because excavation unloading, groundwater drawdown, and river-stage disturbance act simultaneously. This problem is particularly important for foundation pits constructed near existing pile-supported buildings, yet the combined effects of excavation sequence, pit spacing and excavation depth under river-connected gravel aquifers remain insufficiently quantified. This study fills the research gap on the seepage–stress-coupled deformation mechanism of adjacent building piles under multi-pit excavation in highly permeable gravel strata, and quantifies the spatial superposition effect of excavation disturbance. In this study, a three-dimensional seepage–stress-coupled finite-element model was established for the Yidu Green Intelligent Shipbuilding Industrial Park project on the right bank of the Yangtze River. The model was validated against field monitoring data from the slipway pit excavation, and comparisons show that the relative errors of pile horizontal displacement and ground settlement between simulation and measurement are both less than 8%, verifying the reliability of the numerical model. The validated model was then used to evaluate single-pit excavation, different multi-pit excavation sequences, pit group spacing, excavation-depth ratio and steel sheet pile parameters. The results show that pile deformation is controlled not only by the excavation of an individual pit, but also by the interaction between pit groups located on opposite sides of the building. Simultaneous excavation reduced the peak horizontal displacement of the adjacent building pile by 45.7% compared with single excavation of the slipway pit and by 31.6% compared with the slipway-first sequence. For pits on the same side of the building, a far-to-near excavation sequence produced the smallest pile displacement and settlement. The inter-pit ground deformation changed from heave-dominated to settlement-dominated when the spacing increased to approximately 90–100 m. The research results can provide reference for deformation control and safety assessment of adjacent buildings during multi-pit excavation in similar highly permeable gravel areas. These findings indicate that coordinated excavation sequence and spacing control can effectively reduce deformation risks in waterfront multi-pit projects, although the proposed thresholds should be verified for different layouts, geological conditions and hydrogeological conditions.