Wool Old Bridge restoration

Wool, United Kingdom

Year

November 2018

Duration

5 months

Cost

£380,000

Location

United Kingdom

Project achievements

Restoration of a listed bridge and well-loved landmark

Wool Old Bridge is a 16^th century, grade II* listed, six-arch bridge that partially collapsed in January 2018. Temporary works in the form of bagged stone were lifted into position to prevent further failure while a solution was designed.

A temporary dam was installed in July 2019, diverting the River Frome through the undamaged section of the bridge to allow demolition, stabilisation of the damaged arches and site investigations to begin.

This was carried out under an archaeological watching brief as the structure is an at-risk heritage asset. Dressed stone was recovered from the riverbed for reuse while a final design was refined.

The permanent repair consisted of casting fibre-reinforced concrete inverts, a steel-reinforced concrete cantilever retaining wall, with a sheet piled toe and stone cladding. The scheme was delivered in 20 weeks.

Did you know …

During the Second World War, the end arches and the north and south approach of Wool Old Bridge were widened and the parapets removed for the passage of tanks and other large military vehicles for the D-day assault.
The recovered ashlar stone was supplemented with stone sourced from the same Purbeck-Portland bed on the Isle of Purbeck as that originally used.
Over 1,100 million litres of water was pumped out of the working area over the 20-week construction.

Project achievements and benefits

The bridge is an Elizabethan structure that features in Thomas Hardy's novel, Tess of the D'Urbervilles, and is a well-loved landmark in the local area.

A temporary footbridge was installed on the downstream side of the bridge so that a crossing remained throughout construction. The scheme generated interest from residents, businesses, military historians and the daily troop of dog walkers.

In recognition of this, the local primary school was invited to tour the site to inspect the substructure normally hidden beneath the river. While stakeholder engagement is key in any project, this was an opportunity for students to see and touch civil engineering on their doorsteps.

The value of this was recognised by local residents who came to watch the dam being removed. As Dorset County Council is a member-led organisation, it was essential to engage with and get the support of councillors who represent their constituents.

This approach can be seen by the construction delivery team, whose principal contractor used social media on behalf of the client to engage with the local community. Working towards shared outcomes is one of the benefits of the mixed economy delivery model adopted by Dorset Highways.

How the work was done

The recovered stone was supplemented with stone sourced from the same Purbeck-Portland bed on the Isle of Purbeck that the original bridge used. Local stonemasons were used to cut the replacement ashlar and voussoir stone.

Once the failed material had been cleared, trial holes were excavated to establish the construction of the remaining structure. These showed that the six-span stone arch bridge had been founded on timber foundations for over 500 years. During the Second World War, the end arches were widened and the parapets removed for the passage of tanks to the Armour Centre at Bovington.

Due to the listed status of the structure, consent was required from Historic England for the scheme.

The management system put in place by the design team has since been recognised as a national model for other at-risk heritage assets. It included a desk-based assessment of the structure to establish baseline conditions, LiDAR survey of the river bed, archaeological watching brief during the construction phase and aerial photography.

While this fed into the construction phase plan, it also influenced the evaluation of the sustainability of the structures management regime. The archaeological investigation was completed with a level 4 investigation, providing a reference of the works for this important heritage asset.

The permanent and temporary works were done in consultation with the Environment Agency, along with consideration of casting new inverts on the remaining four arches, silt clearance and realignment of 150m of the river upstream of the structure.

The reinstatement of this crossing point complimented an upgrade to an important cycle link between Wool Railway Station and Bovington. The path was originally constructed more than 20 years ago but had become overgrown and narrow by current standards. A popular route with cyclists and walkers, the new provision has been well received.