Study on the cooperative supporting effect of a pile-anchor support system in a deep and large foundation pit

Deep excavations in soft soil often face a conflict between strict deformation control and the need for internal construction space. To explore whether a pile-anchor support system can provide a balanced solution, this study investigates a deep and large foundation pit in Yancheng, China, where SMW retaining piles, a reinforced-concrete bracing level, and two rows of large-diameter jet-grouted anchors were adopted. Three PLAXIS 3D models were established for the pile-anchor-bracing, pile-bracing, and pile-anchor systems under the same excavation conditions, and the numerical results were validated against field monitoring data. The results indicate that all three systems exhibit a bulging deformation mode of the retaining piles, but the deformation pattern of the pile-anchor support system is much closer to that of the pile-bracing system because the bracing member provides a stiffer near-pit restraint and alters the bending-moment distribution of the pile more effectively than the anchors. Compared with the pile-anchor system, the combined system significantly reduces horizontal displacement while preserving more construction space than the pure bracing scheme. The results indicate that the pile-anchor-bracing system provides improved deformation control compared with the single-support systems under the same excavation conditions. The study further clarifies the cooperative mechanism between anchors and bracing members and proposes a normalized comparative indicator for evaluating the synergy effect of combined support systems. The applicability of this indicator is project-dependent and should be further verified in future studies.