ABSTRACT
The provision of a fixed link between the UK and French shorelines represented a major engineering challenge for tunnelling engineers, and a challenge for which there is only one precedent. The SOkm-long Seikan tunnel, which connects the Japanese islands of Honshu and Hokkaido, crosses the 23kmwide Tsugaru Straits with water depths up to 140m, and took 20 years to construct. The principal risk in constructing such long submarine tunnels is irruption at high pressure from the sea should unexpectedly bad local ground conditions be encountered. It is the duty of the tunnelling engineer to investigate and evaluate the likelihood of such risks and to ensure that they are controlled by the chosen design and construction method.
