The Shetland Islands are set for a new network of underwater road tunnels. Once built, well-maintained concrete waterproofing systems may have a fundamental role to play in ensuring they are kept safe as they pass under the sea.
Councillors in the Scottish archipelago have voted to explore funding options for the 1.5 billion project to link several of the islands:
- Shetland’s Mainland
- The island of Yell
- The island of Unst, the northernmost part of the UK, where Britain’s only spaceport is based
- These connections may be followed by Whalsay and Bressay.
The project is expected to cost less than replacing old ferries. Moreover, unlike ferry services, tunnels will be able to offer safe passage between islands in any weather.
The inspiration for the idea comes from the nearby Faroe Islands, where there is now a network of more than 20 tunnels, including four under the sea.
Among the features of the Faroes system is the world’s only undersea roundabout, but building and maintaining underwater tunnels requires careful construction and good maintenance, with regular concrete condition surveys among the necessary measures.
How Can Concrete Waterproofing Protect Underwater Tunnels?
Concrete waterproofing can play a huge role in this, both on land and under the sea, although for obvious reasons a breach under the sea would have far worse consequences.
Not all the Faroese tunnels are made with concrete lining. Indeed, some of the land-based tunnels under mountains have been cut out of the bare rock with no smooth sides.
Such tunnels exist in the UK as well, but in all such cases, the absence of concrete lining or water protection would be an indication that the rock is impermeable.
When tunnels are cut through solid rock, surveys can indicate if there is porous rock or aquifers before they are excavated. In such cases, the use of pre-grouting can reduce water ingress before more substantial waterproofing is applied following excavation.
What challenges may be faced by engineers excavating the Shetland tunnels remains to be seen. But if there is a threat of water ingress, there will also be ways that the tunnels can be protected and maintained to keep them dry.