The Shetland Islands Council (SIC) is currently examining an ambitious plan that, if approved, could see two subsea tunnels constructed that will link the islands of Unst to Yell and Yell to the Shetland Mainland.

Norwegian consultant OT Blindheim, has undertaken a feasibility study that estimates the planned 2.6km and 4.5km long tunnels combined could cost as little as US$51.8M.

The first tunnel would be the shorter 2.6km long Unst to Yell link. The channel depth along the proposed alignment is between 35-40m with around 10m of soft marine soils overlying hard rock. The $21M price tag includes excavation by drill and blast and necessary ground support through anticipated areas of weakness.

The second bore between Yell and the Shetland Mainland is 4.5km long through a deeper channel, up to 44m, and is estimated to cost $35M using the same techniques. Less details are known about this alignment.

OT Blindheim has suggested that a more comprehensive geotechnical investigation be carried out, confirming the low cost of constructing the scheme. This should include detailed seismic refraction surveys and rock coring along both tunnel routes. The consultant stressed that the estimates are not speculative and are based on the company’s experience on similar projects in similar conditions in Norway, Iceland and the Faroe Islands.

As T&TI went to press SIC was deciding whether to invest the further $1.4M needed to undertake the more detailed geotechnical investigation.

The scheme has been on the drawing board for some years, originally UK consultant Halcrow carried out a basic desktop study that estimated a far higher cost for tunnels. The Halcrow study chose a much longer tunnel route, the actual $/m average was said to be similar.

SIC project co-ordinator, Michael Craigie is hopeful for the scheme but told T&TI that funding could be difficult as tolls are not expected in the tunnels and that the project cost would use up all the council’s $35M/year capital programme for several years.

The plan is to provide an alternative to the ferry service that is the inhabitants only link between islands. This is regularly affected by high seas.

Related Files
Figure 1: Location map of proposed subsea tunnels