Abstract: The Pearl River Estuary subsea tunnel of Shenzhen-Jiangmen railway, with 1.06 MPa ultra-high water pressure, 115 m buried depth, and highly complex geological conditions, has big construction challenges. In this paper, the following key design aspects for subsea railway tunnels under high water pressure are studied, with the Pearl River Estuary subsea tunnel as an example, by means of engineering analogy and comparison and contrast: the selection of the tunnel construction method, the design of the tunnel sections constructed by the shield method, the design of the tunnel section constructed by the mining method, the docking between the tunnel section constructed by the shield method and that constructed by the mining method, and the dewatering for the construction of the inclined shaft. Based on the geological conditions, the authors propose shield method + mining method for the construction of the tunnel. The results demonstrate that: (1) For tunnel sections constructed by the shield method, the thickness of the segments is designed according to the maximum water pressure, double rows of EPDM elastic sealing gaskets are designed for the waterproofing of the segment joints, and cutter replacement under atmospheric pressure, cutter replacement under reduced pressure, and shield repairing points are suggested to replace the cutters. (2) For the tunnel section constructed by the mining method, the water pressure on the tunnel structure, which is determined according to the geological conditions, is set at 0.2 MPa, advance grouting is recommended to control the drainage amount, and repairable drainage systems are recommended. (3) Shield assembly cavern is recommended with priority, with conditions for in-situ destructive demolition of the shield reserved. The inclined shaft of the tunnel passes through permeable strata, and dewatering is recommended to ensure the stability of the strata.

Key words: railway tunnel, subsea tunnel, shield method + mining method, waterproofing and drainage, complex environment, high water pressure