Assessing and predicting surrounding rock settlement troughs in the subsea tunnel: A case study of Haicang Tunnel

To ensure the safety of subsea tunnel construction, it is crucial to prevent extreme deformation of the surrounding rock. An assessment and prediction study on the surrounding rock deformation induced by the excavation of the subsea tunnel using the three-bench method was conducted, based on Haicang Subsea Tunnel in Xiamen, China. A series of numerical simulations and on-site monitoring were conducted to reveal the evolution of the displacement field of the surrounding rock. The influences of various factors on the settlement trough of the surrounding rock above the subsea tunnel were also investigated, including seawater, bench length, and bench spacing. The rapid ring closure of the primary support by adopting short benches is imperative to control the arch settlement and settlement trough width. The settlement resulting from the excavation of the upper and middle benches contributed to 90% of the total deformation, as revealed by both numerical simulation and in-situ monitoring. Subsequently, an empirical formula was proposed to predict the settlement trough curves of surrounding rock at different depths above the seabed tunnel.