LARGE UNDERSEA TUNNELS AND THE PROGRESS OF TUNNELING TECHNOLOGY

Large undersea tunnels constitute key parts of some of the biggest infrastructure projects of our time. They involve an extraordinarily high risk and cost. To reduce both risk and cost, innovative technical solutions often must be sought and developed However, the significance of these innovations is seldom limited to a single tunnel. In most cases, they represent major contributions to tunnelling technology in general, and therefore are studied by the profession with great interest. The main features that make deep underwater tunnels different from land tunnels are the reduced accuracy of underwater geological investigation, great length of uninterrupted single drives; high pore water pressures and seepage gradients at the tunnel elevation; large long-term loads caused by hydrostatic pressure; and the requirement for high speed tunnelling systems in order to reduce construction time and, thus, the cost of financing. This paper reviews some of the lessons that have been learned by tracing a few emerging trends and indicating areas where solutions are still needed.