Study on structural mechanical characteristics and safety warning of NATM tunnel in aquifer

With sustainable developments in transportation facilities, the construction of the undersea tunnel has become inevitable. Controlling the construction and operation of the undersea tunnel structures dynamically and ensuring their safety is of primary concern. Therefore, using the rich water mountain section of the Lujiazhi subsea tunnel constructed by NATM (New Austrian Tunnelling Method) as a case study, an intelligent real-time tunnel health monitoring system integrating tunnel monitoring, wireless transmission and safety assessment was developed. The monitoring results show that the surrounding rock water pressure, earth pressure and stress of the secondary lining structure experienced stages of rapid change, continuous change and stability. The tunnel substructure is relatively weak as a whole, and the left invert is the weakest part of the whole structure. It was suggested to optimize and reinforce the tunnel substructure accordingly. The rationality of the tunnel drainage system and reliability of field test data are verified by numerical simulation. Finally, the real-time fuzzy comprehensive evaluation model of tunnel operation safety conditions based on online monitoring data is established to realise the real-time evaluation and early warning of Lujiazhi tunnel structures' health conditions.