Mechanism of Ground Deformation Induced by Freeze-Sealing Pipe-Roof Method: Case Study of Gongbei Tunnel of the Hong Kong–Zhuhai–Macao Bridge

Abstract This study investigates the mechanism of ground deformation induced by the Freeze-Sealing Pipe-Roof (FSPR) method, with the Gongbei Tunnel of the Hong Kong–Zhuhai–Macao Bridge as a case study. Controlling ground deformation is crucial for tunnel construction safety. However, the complex mechanisms of ground deformation and the quantitative proportions of contributing factors have not been fully elucidated in previous studies. To address this, a theoretical model based on transient heat conduction in a semi-infinite space was established, in which the frost heaving coefficient is formulated in terms of the maximum frost heave rate and shows an inverse correlation with the thermal expansion coefficient. The maximum frost heave rate was experimentally obtained from frost heave tests on saturated soil under water replenishment. A three-dimensional (3D) finite-element model implemented in Abaqus was subsequently developed and validated against field monitoring data from the pre-excavation freezing phase. Numerical results indicate that vault settlement peaks at 28.8 mm, consistent with field observations. Crucially, the mechanism of ground deformation can be quantitatively decomposed into three primary sources: frost heaving (39.6%), lining self-weight (38.8%), and support effect (21.6%). The findings reveal that in shallow-buried and water-rich tunnel construction, although lining self-weight and support effects are constrained by structural requirements, the dominant frost heaving effect is a viable control point that requires particular attention. These findings provide a refined theoretical basis and technical guidance for optimizing freezing parameters to mitigate environmental risks in similar large-scale subsea tunnels using FSPR technology.