The development of underground spaces in mega-cities necessitates understanding the interaction among various underground structures. Soil acts as the fundamental medium in bearing and transmitting forces during the construction of these structures. In shield tunnels, the deformation of adjacent soil is a primary concern. or underground structures with piled raft foundations, this deformation directly impacts the foundation’s bearing capacity and causes differential deformation. This consideration becomes especially crucial for large-diameter shield tunnels when intersecting with piled raft foundations. To address this issue, the study examines a case of a mega-diameter shield tunnel intersects a piled raft foundation, which is the built for an underground railway station. The research focuses on soil deformation between the tunnel and the structure during construction, analyzing the variation of pile neutral points across the foundation based on soil deformation. A method is proposed to rapidly predict incremental negative frictional resistance of piles due to tunnel excavation, guided by soil deformation. The study clarifies the specific range of tunnel excavation’s influence on pile-bearing capacity, offering practical insights and potential theoretical guidance for similar future projects.

As urban rail transit networks become denser, twin tunnels are increasingly constructed in close proximity above existing operational tunnels, making ground surface settlement control and existing tunnel protection critical challenges. Previous studies have mainly focused on the adverse effects of new tunnel excavation on existing tunnels, whereas the reverse mechanism—namely, how an existing tunnel, as a stiff continuous structure, constrains surrounding ground deformation and thereby affects surface settlement—remains insufficiently understood. Clarifying this mechanism helps explain differences in settlement between cases with and without an underlying existing tunnel and provides a basis for optimizing the overcrossing geometry, predicting settlement, and managing construction risk. This study combines numerical simulation with theoretical analysis to investigate the effects of vertical clearance, center-to-center spacing of the new twin tunnels, staggering distance between excavation faces, and crossing angle on soil deformation within the construction-affected area. The settlement control mechanism induced by the constraint of the existing tunnel is identified, and a method for calculating surface settlement is proposed. The numerical results indicate that the existing tunnel reduces surface settlement. This response is interpreted as a combination of local constraints on surrounding ground deformation and global beam-like restraint, thereby reducing ground surface settlement. Vertical clearance, the horizontal spacing of new twin tunnels, and crossing angle govern the settlement response by altering the constraint intensity, superposition of settlement troughs, and restraint provided by the embedded tunnel lining/segments, respectively, whereas the staggering distance between excavation faces mainly affects settlement evolution with excavation advance. Because the settlement profiles obtained with and without an existing tunnel are approximately linearly related, the proposed calculation method does not explicitly account for the settlement reduction associated with the existing tunnel. Verification using an engineering case study indicates that the method is suitable for preliminary settlement prediction and risk assessment in similar projects.

In this study, we explore the stability of shield tunnel faces excavated entirely within confined aquifers through a combined physical investigation. A series of orthogonally designed model tests were performed to examine how the hydraulic head difference (Δh) and aquitard thickness (M) jointly influence face stability and seepage behavior. Our results reveal a distinct concave-downward pore-pressure profile and a steep hydraulic gradient immediately ahead of the excavation face. Excavation-induced stress redistribution was largely restricted to the aquifer, whereas the overlying aquitard exhibited negligible disturbance due to its low permeability and higher strength. The evolution of stress disturbance followed a three-stage process encompassing initial disturbance, progressive development, and large-scale destabilization. Deformation contours exhibited a conical failure zone with normalized width and height ranging from 0.7D to 1.0D and 1.7D to 1.86D. Surface settlements remained within ±1 mm, confirming that deformation was effectively confined below the aquitard. Numerical simulations reproduced the overall hydro-mechanical response, validating the experimental observations but slightly overpredicting support pressures due to the absence of arching effects. The findings highlight Δh/M as the dominant control parameter, with aquitard thickness exerting a moderating influence.