Tunneling activity inevitably induces soil stress redistribution and ground deformation, which may affect adjacent existing pile foundations. Since many previous studies have mainly focused on circular tunnels, the effects of quasi-rectangular shield (QRS) tunneling on adjacent existing pile foundations are not well investigated and understood. In this study, a series of physical model tests were carried out to investigate the response of a single pile and pile group subjected to newly QRS tunneling beneath an existing circular tunnel in dry sand. Two distinct underpass cases were considered: an orthogonal underpass (QRS tunnel axis perpendicular to the circular tunnel axis) and an overlapping underpass (QRS tunnel axis aligned with the circular tunnel axis). The test results indicate that QRS tunneling-induced ground surface settlement and single-pile settlement in the overlapping underpass case were 3.6 and 1.2 times that in the orthogonal underpass case, respectively, with a narrower settlement trough. The axial force distribution along the single pile remained qualitatively consistent in both underpass cases, consistently exhibiting a downward load-transfer mechanism, and further leading to a monotonic growth pattern in axial force with progressive QRS tunnel excavation. The additional stress of the single pile was consistently higher in the overlapping underpass case, which had maximum axial force, negative bending moment, and maximum positive bending moment increases of 20%, 13%, and 6%, respectively, relative to the orthogonal underpass case. The front pile in the pile group exerted a pronounced shielding effect on the rear pile, while the restraining action of the pile cap also contributed measurably to the overall pile responses.

Tunnelling-induced safety risks from adjacent piles have become increasingly severe with the rapid development of urban underground space. Model tests have become essential for revealing the complex pile-tunnel interaction mechanism. This paper reviews the research progress of model tests on the influence of single-line tunnelling on adjacent piles, focusing on test soil materials, tunnel simulation methodologies, analysis of test results, and research prospects. However, current model test studies are constrained by several critical limitations, including insufficient similarity between soil materials and prototype conditions, and overly idealized simulation of tunnel excavation. This paper identifies a significant research gap: the inability of current volume-loss techniques to capture 3D dynamic factors (e.g., face pressure and grouting timing) and the lack of meso-scale observation at the pile-soil interface. This review provides a systematic synthesis of these methodological challenges and proposes future research prospects to provide a more scientific basis for engineering design and risk control.

Existing studies predominantly investigate the impacts of tunnel or excavation on pile foundations in isolation, whereas actual engineering projects often involve sequential or simultaneous excavation of tunnels and excavation. This study focuses on the effects of combined tunnel and excavation unloading on adjacent pile groups in clay strata. Constant-gravity physical scaled model tests and three-dimensional numerical simulations are conducted, accounting for the time-dependent effects of clay excavation unloading and soil stiffness characteristics under small-strain conditions. The additional responses of pile foundations and the evolution of excess pore water pressure dissipation during excavation unloading are systematically analyzed. The results reveal that the type of pile foundation surrounding tunnels and foundation pits has a minor influence on surface settlement. Both tunnel and excavation induce tilting of pile groups toward the unloading zone: the tilt increases continuously to 0.12% of the pile spacing during tunnel excavation, gradually decreases to 0.05% of the pile spacing during excavation, and a net tilt toward the tunnel side persists in the end. Pile foundation type affects the axial force variation pattern of piles. Owing to the shielding effect of rear piles in the group, the maximum negative bending moment of the pile group is approximately 29% smaller than that of a single pile, with a large bending moment occurring near the pile head. The presence of excavation support structures and existing pile foundations alters seepage paths of pore water, thereby influencing the dissipation time of excess pore water pressure.

Existing studies often analyze tunnels and excavations as isolated projects, but in practice they are often constructed sequentially or simultaneously. This paper investigates their combined effects on adjacent pile foundations in clay using constant-gravity model tests and 3D numerical methods, considering time-dependent clay behavior and small-strain stiffness. Two combined construction sequences of tunnelling and excavation adjacent to an existing pile were investigated: (i) tunnel excavation followed by basement excavation (i.e., test TEP); (ii) basement excavation followed by tunnel excavation (i.e., test ETP). Results show that construction sequence has little effect on surface settlement but significantly influences pile response. Pile top settlement increases considerably when tunnelling occurs near piles. The TEP sequence reduces cumulative pile top settlement by 0.38% of the pile diameter and reduces the maximum cumulative bending moment by approximately 31% compared with the ETP sequence. Additionally, tunnel and excavation construction generate negative excess pore water pressure in the surrounding soil, which dissipates over time. The pressure increases with proximity to the tunnel face or excavation base.