Client & Design: British Waterways – East Midlands
Construction: Galliford Try
The Clark’s Bridge refurbishment project was carried out to strengthen and repair a Grade II Listed structure on the Grantham Canal, a remainder canal in Nottinghamshire. It was a joint project between British Waterways East Midlands and Galliford Try Construction.
The structure is a masonry arch bridge, constructed of handmade bricks with lime mortar bedding circa 1797 for farm access. Prior to repair it had a reduced capacity, had been highlighted through British Waterways’ inspection programme as a structure in need of repair, and was on the local council’s buildings at risk register.
West Elevation – before
Saddling was the preferred strengthening option as the works were relatively straightforward on the lightly trafficked structure, and the saddle would be hidden once works were complete. This option also significantly prolonged life for a minimal additional present day cost. Additional work included the repair of damaged brickwork on the parapets and spandrel walls, replacement of the arch ring face with blue engineering bricks and the reintroduction of a continuous blue brick stringcourse at the base of the parapets. The parapets themselves were in such poor condition that they were taken down and rebuilt in their entirety, to the original bond pattern. The underside of the bridge was re-rendered with hydraulic lime mortar as repair of this brickwork would have been difficult to achieve
Re-rendered underside of the bridge
(showing bat box entrance)
The correct choice of materials was an important aspect of the works. The aim was to maintain the heritage of the structure and to minimise the volume of material either taken off site or imported. Damaged bricks were carefully removed, cleaned, turned and re-used. Where this was not possible due to excessive damage, they were replaced with reclaimed bricks selected to closely match those in the existing structure. The damaged bricks were crushed and re-used in the fill material; the remaining fill was made of recycled material. FSC timber was used for both temporary and permanent works.
Representative samples of the existing lime mortar were sent for analysis to determine a matching mix. As part of the Listed Building consent, the lime mix and reclaimed brick type was agreed with the local planning authority. The lime mortar was protected with sheeting as the works were undertaken during the winter months. During the coldest period the structure was protected by tented scaffold and heating.
The props holding the intrados up during the works were drilled and fixed to the abutments in order to minimise disturbance to the waterway. Scaffold was close boarded and covered with plywood sheeting to retain debris. Debris netting was also installed to prevent materials from falling into the waterway
The bridge was enclosed in a heated tent to protect the lime mortar during a cold spell. Maintaining a free waterway by keeping the propping out of the water minimised disruption to canal wildlife.
The site lies within a county wildlife site, and the adjacent (privately owned) farm is part of a countryside stewardship scheme. Disturbance of the surrounding landscape, including trees and hedges, was kept to a minimum. The top of the bridge was covered with Suretrac, an environmentally friendly material, and seeded with locally sourced grass and wildflower species. A survey determined bats were using the area, but not the bridge. A bat box has been cast into the concrete saddle and is accessed from the intrados via a small opening in the lime render. An interpretation panel was installed to assist understanding and appreciation of the structure
West Elevation – after