Research on the influence of pile diameter on the pile-anchor support system for deep foundation pit adjacent to the existing structure

The excavation of complex deep foundation pit poses significant risks to the safety of adjacent existing structures. To investigate the force and deformation characteristics of deep foundation pit, this study focuses on the pile-anchor support system of a deep foundation pit for a third-line ship lock on the Xiangjiang River. Model tests and numerical modeling analyses were conducted to evaluate the influence of pile diameters (1.0 m ≤ d ≤ 2.0 m) on the force and deformation characteristics of pile-anchor support system in deep foundation pit adjacent to buildings. The results indicate the following: (1) The variation pattern of horizontal displacement at the top of pile in the model test is consistent with that observed in the numerical simulation. The bending moment of the pile body exhibits an “S”-shaped distribution, confirming the reliability of numerical model. (2) The horizontal displacement curve of pile body presents a “bulging belly” shape, with smaller displacements at the top and bottom and larger displacements in the middle. The curvature of displacement decreases as the pile diameter increases. (3) Larger pile diameters result in greater bending moments in the pile body, smaller changes in the positions of positive and negative bending moment extremes, and reduced surface settlement. (4) The uplift at the bottom of foundation pit initially decreases and then increases, forming a “hooked” curve. The influence of pile diameter on bottom uplift is relatively minor. (5) Larger pile diameters promote a transition in the active failure mode from semi-infinite soil to finite soil, with d = 1.5 m serving as the critical value for finite soil conditions. (6) Based on economic considerations, d = 1.5 m is determined to be the optimal pile diameter. (7) The active deformation sliding surface of finite soil behind piles is a curve or polyline that is higher than the heel of wall and returns to the adjacent buildings. This study provides valuable experimental data for investigating finite soil deformation behind piles in the pile-anchor support system for deep foundation pit, offering both theoretical significance and practical engineering value.