Green light for Stonehenge Tunnel16 November 2020
UK Transport Secretary Grant Shapps has given the go-ahead for work to start on the 3.2km Stonehenge Tunnel which will form part of the A303 Amesbury to Berwick Down carriageway improvement scheme in Wiltshire, England.
Highways England welcomed the decision for the £1.7bn (US$2.2bn) scheme and said it would unlock congestion and transform journeys for millions of people using the A303 in southern England.
The scheme’s twin-tube tunnel is expected to have a transformational impact on the landscape, given that the current A303 features one of the UK’s busiest sections of single-carriageway. With around 25,000 vehicles using it daily, it passes within 160m of the Stonehenge heritage site.
Longer than the previously proposed 2.9km tunnel length, the revised proposal has been extended to 3.2km to optimise the tunnel portal locations, protect heritage and best integrate the tunnel into the landscape.
The alignment geology is mainly chalk (white limestone) with a very high groundwater table. However, previous geological studies revealed that rather than the normal chalk encountered in much of the UK, here there is a 15m band of phosphatic chalk which is interspersed with weak and poorly-banded sand and silt layers. This rare phenomenon will have a significant impact on the TBM-type chosen. Encountering radon gas during tunnelling is also a possibility.
Highways England has been progressing the procurement process for the main works contract for the scheme and is participating in dialogue with three bidders before they submit their final tenders. The preferred bidder is expected to be announced in 2021, with the main five-year construction phase expected to start by 2023.