Abstract: The sea-crossing tunnels are developing rapidly in China. The proposed Qiongzhou Strait Passage and Bohai Strait Passage will face technical difficulties such as ultra-long distance and ultra-high water pressure tunneling. In the current research and practice, the water pressure of shield tunneling is about 0. 8 MPa, and the distance of one tunneling is within 8 km. Based on the engineering background of the Qiongzhou Strait Middle Line Shield Tunnel (water pressure of 1. 2 MPa, tunneling length of 12 km), the engineering analogy and construction key technologies are used to analyze the feasibility of high-pressure long-distance shield tunneling technology to solve the problem of safe tunneling and safe service during the operation of the shield tunnel under high water pressure. The following technologies, i. e. shield active tool change, passive saturation diving belt pressure tool change, integrated tool change technology for freezing and strengthening in extraordinary state and the comprehensive technology of replaceable seal,are put forward, which can guarantee the shield tunneling for long distance. Meanwhile, an ultra-high water pressure shield composite segment lining and a combination of internal and external waterproof structures are proposed to ensure the safe operation of the shield segment structure under ultra-high water pressure.

Key words: subsea tunnel, high water pressure, shield tunnel, long distance tunneling, cutting tool replacement