Implications of the collapse of the de la Concorde underpass

Taw Bridge is a five-span crossing of the Taw estuary in Devon. It forms part of the Barnstaple Western Bypass, a 2.7km relief road scheme, for which a design and build contract was awarded by Devon County Council to Edmund Nuttall Ltd in 2004. The bridge was opened in May 2007. The bridge is a cast in situ post-tensioned concrete box girder with a total length of 409m. The majority of the structure is built by the balanced cantilever method over the estuary, which is a designated Site of Special Scientific Interest (SSSI). The substructure comprises two abutments and four piers, the latter being constructed within the estuary using cofferdams. At tender design phase it was recognised that building a temporary causeway connecting the cofferdams to the shore would offer substantial benefits to the contractor and to residents by reducing vehicle movements through the town. The paper presents some of the unusual aspects of the design and construction of the bridge, its materials and the construction techniques assumed in the design and used in the execution. Malcolm Fletcher, MBE, MSc, FREng, FICE Halcrow, Consultant Raj Janmejay, MSc(Bridges), MIE(I) Senior Bridge Engineer, Halcrow Paul Wright, BSc(Hons), MICE Engineer, Halcrow