Soil Deformation Investigation of a Piled-Raft Foundation Pit Under-Crossed by a Super-Large Diameter Shield Tunnel

Abstract

In recent years, there has been a rise in the construction of expansive underground structures and shield tunnels with exceptionally large diameters. These projects introduce unique challenges regarding their impact on the surrounding soil and structures, which differ from those typically encountered in conventional shield tunnels. However, the existing body of research in this specific domain remains insufficient. When such tunnels intersect deep foundation pits supported by piled-raft foundations, the discrepancies in soil deformation can become even more pronounced. At present, there is a dearth of research on the underlying principles governing these differences, and theoretical investigations have not kept pace with practical engineering applications. Consequently, the existing settlement prediction methods employed for diverse projects need to be reevaluated and adjusted to accommodate the distinctive characteristics of each individual project. Regarding the engineering focus of this paper, it is crucial to recognize that soil subsidence in the pit bottom has a significant influence on the mechanical response of the piles. Consequently, the implementation of targeted correction measures remains consistently important. Based on this concept, this paper focuses on a super-large diameter shield tunnel project that under-crossed a deep foundation pit with a piled-raft foundation. The influence of different construction methods on the settlement law of the soil at the bottom of the deep foundation pit is discussed after verification of the accuracy of the model through numerical simulation and field monitoring data. Additionally, two correction coefficients that consider the project’s load characteristics are proposed in this research. These coefficients were used to correct the surface settlement curve. The corrected soil settlement curve at the pit’s bottom can successfully reflect the numerical simulation results, which in turn can reflect the mechanical response of the pile under the influence of tunnel excavation.

Assessment of the Influence of Tunnel Settlement on Operational Performance of Subway Vehicles

“…To expediently determine track irregularity prompted by tunnel settlement, an analytical model of settlement-track irregularity was devised. The resolution of the model was premised on the following assumptions: (1) The mortar layer beneath the track plate is treated as a Winkler elastic foundation; (2) No coupling relationship exists between the deformation of the shield segment and the track.…”

“…Factors such as falling groundwater levels leading to segment subsidence, groundwatertriggered segment floatation in water-rich strata, and soil deposition-induced segment subsidence, can impact the smoothness of subway lines. This may result in a gamut of issues, including degradation of train running smoothness, comfort, and safety [1][2][3][4][5][6].…”