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Thelwall Viaduct. The £5 million viaduct was opened in July 1963 by Ernest Marples, the then Minister of Transport, and carries the M6 mororway over both the river Mersey and the Ship Canal. The bridge is 4,417 feet long and gives a clearance over the canal of 93 feet. The bridge is built in the same manner as the high level bridge at Barton and carries the roadway over thirty six spans supported on reinforced concrete piers. The upper sections of the bridge are of welded steel construction with a concrete decking. The original bridge was designed to carry three lanes of traffic in each direction but this soon became insufficient and a second bridge, of similar construction, was built immediately alongside it (on the eastern side). The new bridge was opened in 1995 and the two bridges between them now provide the M6 with four lanes in each direction. The newer of the two viaducts carries twenty six completely-welded spans, with
the largest span, at 71 metres in length, requiring the deployment of an 800-tonne
crane to lift it into place. The viaduct is constructed of six lines of girders, site
welded between cross heads. At 1380 metres in length it is the longest continuously welded
structure of its kind in the UK.
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