Emergency temporary works to a vital road bridge carrying the B1389 over the Blackwater Rail Trail.
Client: Jackson Civil Engineering
Main Contractor: Jackson Civil Engineering
Value: £440,000 (temporary works only)
The bridge, circa 1848, was a single span structure with a deck comprising of eight cast iron beams with brick jack arches. Previous strengthening works, by the provision of steel support trestles installed in 1942 and 1992, created a three-span structure.
In 2014 cracks were discovered in the bottom flanges of the cast iron beams, and emergency temporary supports were installed. The B1389 is a critical link road and an A12 strategic diversion route, with no feasible diversion route able to cope with peak and normal daytime traffic flows, and as such there is a requirement to keep the road open to traffic. To achieve this, Essex Highways proposed to replace the bridge by constructing a new reinforced concrete box structure under the existing bridge, with the resulting void between the old and new being filled with foamed concrete.
To enable construction of the new structure required the removal of the existing steel trestle supports and props. Sweco devised a new temporary propping system, comprising of a series of steel portal frames, that could be installed in phases in and around the existing trestles and props. Bridge loads were transferred to the new system by synchronised jacking prior to removing the old props and trestles. The new temporary works were installed with only two weekend road closures.
Technical approval was by the local highway authority in accordance with Highways England’s design standard BD2/12 Technical Approval of Highway Structures. The design underwent an independent Category 3 check.