The project involved the restoration of a Victorian structure built by Arrol Brothers in 1889 over two watercourses - the River Lea and Bow Creek, a tributary of the Thames. The movement of trains on the structure was subject to severe speed restrictions (10 mph), due to the general deterioration of the structure, particularly the rail bearers and wind bracing.
Restoration was a challenge, as additional temporary loads to facilitate the work were not permitted on the existing structure. This restriction was overcome by providing an independent support temporary enclosure to the bridge for the duration of the work, comprising 500 tonnes of scaffolding supported entirely on temporary piled steelwork dolphins.
Tony Gee and Partners were commissioned to design a scheme to overcome problems arising from low headroom, work in tidal and busy non-tidal waterways, an adjacent Railtrack bridge (1.8m separated both structures) and general lack of access, especially for craneage.
Solutions for the piled dolphins and fendering system were then modelled and tested at HR Wallingford to monitor tidal flows during flood conditions to identify potential adverse erosion of the river bed.
The installation of the temporary spans was a combination of jacking beams supporting the formwork from pontoons and sliding over temporary trackways. The real challenge came in placing and positioning the steelwork to fit in operationally short tidal windows in Bow Creek.
The contract was not 24/7 in its operation, but arguably more complex, with what equated to three separate operations taking place concurrently. There were the normal site working hours five days a week; there was the continuous run of Engineering Hours work which took place when the Underground was shut down; and finally the 52 (18No) and 27 (4No) hour possessions which took place at weekends.
Typically, the weekend possessions were up to 500 man shifts during each possession. The team successfully completed all twenty two - handing them all back on time without an overrun - an LUL record!
Procurement Route: Partnering
Sector: Rail
Value: £12 million
