A case study on key techniques for long-distance sea-crossing shield tunneling

The Zhanjiang Bay Sea-crossing Tunnel is the first phase of an ambitious plan of the Golden Triangle Economic Zone in southwestern China and passes underneath the deepest artificial shipping channel with the highest level in Asia. The tunnel is a world-record extralong and small-diameter corridor constructed using an uninterrupted single-end shield tunneling method in subsea soft ground under ultrahigh hydraulic pressure for water conveyance. This case study first highlights the engineering challenges of constructing the sea-crossing shield tunnel in subsea soft ground under ultrahigh hydraulic pressure. A series of key techniques are then investigated and some innovations are proposed to address the engineering challenges in the following four key aspects of the sea-crossing shield tunneling process: (a) optimal design of segmental linings; (b) adaptive reformation of the shield machine; (c) structural construction of deep vertical shafts; and (d) supporting techniques of long-distance advancing. On the basis of the field monitoring and numerical analyses, it is concluded that the implemented key techniques ensure the successful management and control of the engineering challenges in terms of optimizing the segmental lining, selecting the shield machine and constructing the vertical working shaft during the sea-crossing shield tunneling process with limited geological investigation data available under submarine conditions.