Theoretical and Experimental Study on the Control Effect of Isolation Piles on Soil Subsidence Induced by Excavation in Sandy Stratum

To investigate the effect of isolation piles on surface subsidence induced by excavation and to explore the influence of isolation pile layout parameters on the subsidence behind the piles, this study employs a combined approach of theoretical calculation and model testing to systematically analyze the control effect of isolation piles on excavation-induced deformation. Based on a three-stage analysis method, the Kerr three-parameter foundation model is first introduced to solve the deflection differential equation and calculate the lateral deformation of the underground continuous wall induced by excavation. The boundary element method is then used to compute the additional stress near the isolation piles caused by the wall displacement, considering the shielding effect of pile groups. The lateral deformation of the isolation piles due to excavation is calculated, and the boundary element method is applied again to determine the additional stress induced by the pile displacement. Finally, the Mindlin solution is employed to compute the surface subsidence behind the isolation piles. Laboratory-scale experiments on subsidence control using isolation piles are conducted, and the results are compared with theoretical calculations to verify the validity of the theory. The results show that, compared to the condition without isolation piles, the presence of isolation piles reduces the surface subsidence by 0.099 mm. Increasing the diameter, elastic modulus, or pile-to-wall distance of the isolation piles, as well as reducing the spacing between isolation piles, helps reduce both the lateral deformation of the isolation piles and the surface subsidence behind the piles. Under the parameters used in this study, the reduction in lateral deformation of the underground continuous wall reaches 0.112 mm, 0.054 mm, 0.147 mm, and 0.172 mm, while the reduction in subsidence reaches 0.07 mm, 0.027 mm, 0.094 mm, and 0.124 mm, demonstrating significant deformation control effects. The conclusions derived from this study can be directly applied to practical foundation pit engineering. They offer valuable insights for optimizing the selection and arrangement of isolation piles, thereby providing effective guidance for controlling ground subsidence induced by excavation activities on site.