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Bigweir bridge, a grade II listed cast iron bridge faced numerous challenges whilst undergoing crucial restoration work, including remaining open whilst reducing the weight restriction on the bridge and protecting the local wildlife.
Built in 1827, the Bigsweir bridge carries the A466 over the river Wye between Monmouth and Chepstow in the Forest of Dean, a route particularly popular with tourists. Following routine bridge inspections, the structure's paint system was found to be in a very poor condition and once work began, further cracks were discovered.
Gloucestershire Highways team (a partnership between Atkins and Gloucestershire County Council) were responsible for the scheme design, inspections, consents, consultation, procurement and supervision.
A roped access inspection confirmed the details of the existing paint system and identified a number of cracks to the existing cast iron members. Specialist contactors were consulted in order to determine the optimum method of repair, while meeting the requirements of the Conservation Officer.
A number of environmental surveys were undertaken to verify the presence of any protected species in the area, and mitigation measures to minimise the disturbance to bats. Approval for the works was obtained from Environment Agency, Natural England, Wye Valley AONB, and consultation completed with local stakeholders.
To enable the bridge to remain open during the works and safely support the additional weight of the temporary works, Gloucestershire Highways (GH) reduced the existing weight restriction of 17 tonnes to 7.5 tonnes forcing heavier vehicles to divert.
Work was undertaken outside of summer months, to reduce disruption to the large number of coaches using the bridge over the main tourist season. This presented an increased risk of low temperatures and high river levels during winter flooding, so additional control measures were put in place to reduce the impact of these issues on the works.
A detailed review of the previous assessment was undertaken and it was agreed the painting works needed to be carried out in five distinct phases to limit the loading imposed on the structure from the temporary works. Carrying out the works in this way had significant consequences both in terms of cost and programme
Specialist painting contractor, Jack Tighe Ltd blasted off the existing paint system along with any corrosion and repainted the structure using a four coat system (1 primer, 2 MIO Epoxy undercoats, and one Polyurethane finish coat), matching the existing bridge colours.
To prevent contamination of the river below, the blasting and painting works needed to be fully encapsulated as the existing paint system was lead based and the works were over a SSSI watercourse. Extensive preparation of the cast iron surfaces and joints was also required prior to repainting.
Bigsweir Bridge reopened in June 2011 following the works which will greatly extend the life of the 180-year-old structure.
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