Numerical Study on the Influence of Water Level Change on the Stability of Subsea Tunnel Excavation

Subsea tunnels are of great significance for alleviating traffic pressure. However, the notable change of water level under the action of tide inevitably leads to the re-distribution of rock stress and pore pressure. Therefore, understanding the influence of water level change on the stability and failure response of surrounding rock is crucial for ensuring the safety and stability of subsea tunnels during construction. In recent years, the Material Point Method (MPM) has been gradually applied to large deformation geotechnical engineering problems because it can avoid grid distortion. This study proposes using Material Point Method to analyze the damage response of the water level change to the surrounding rock, based on the engineering background of Qingdao Jiaozhou Bay Second Subsea Tunnel. Considering the water level change under different surrounding rock grades, the distribution principle and characteristics of ground settlement, surrounding rock de-formation, and plastic damaged zone are discussed. The results show that the change in water level is not the decisive factor in the stability of the surrounding rock. Instead, coupling the water level change with the poor rock quality and tunnel design is the key to tunnel failures.