Between now and year-end, a contractor in central Liverpool will tear down a viaduct with a replacement value of around $70 million and crush and recycle the rubble as fill for a new highway in the U.K. city. The fate of Churchill Way is one of the most dramatic consequences of a new inspection regime of post-tensioned concrete bridges that emerged from the rubble of collapses nearly 30 years ago.
The defunct contractor G. Percy Trentham Ltd. built Churchill Way, which opened in 1970, to designs by what was then WS Atkins and Partners. Two roughly 240-m-long diverging viaducts were planned as part of an inner beltway that was never completed.
Publication of new official bridge design guide in 2015 prompted Liverpool City Council to recommend upgraded post-tensioned special inspection for post-tensioned structures, including the viaducts. Between early 2016 and December 2018 Amey Consulting Ltd. performed PTSI on Churchill Way. Work ranged from desk studies to intrusive investigations.
The investigations revealed deficiencies so serious that strengthening was deemed not viable, while reconstruction was unaffordable. We “simply have no choice but to take them down as soon as possible,” said Liverpool Mayor Joe Anderson early this year.
The PTSI regime set out in the government's 2015 design guide culminated from work begun after two bridge collapses led to a temporary 1992 U.K. ban on post-tensioned span construction. The 1985 failure of the small Ynys-y-Gwas Bridge in Wales had raised doubts over durability of internal post-tensioning. The collapse seven years later of the Belgian Melle Bridge over the river Schelde confirmed those fears.
Of the U.K.’s roughly 100,000 bridges, an estimated 3,000 were grouted post-tensioned structures. About 600 were owned by the government and the rest by other infrastructure owners. PTSIs during the decade after the Belgian collapse determined about 10% needed attention and others were likely to require remedial work in the future, reports Donald Pearson-Kirk, a technical director at WSP in the U.K.
Since PTSIs until then had inadequately relied on general, non-intrusive inspections, the 2015 guide was “a big step forward,” says Pearson-Kirk. For many engineers in the 1990s, inspections involved learning on the job. Pearson-Kirk had gained experience a decade earlier by probing 88 bridges in Saudi Arabia over a three-year period. At the time, “there was no known way of checking these bridges,” he adds.
Investigations of the Liverpool viaducts involved more than 140 tests revealing multiple flaws, including corroded tendons and symptoms of overstressing, according to LCC. While able to support their own weight, the structures were “not adequate to carry vehicular or pedestrian live loads,” reported the council.
For the $8.3-million demolition in the city centre, Amey and the contractor Graham Construction Ltd. devised an operation minimizing road closures and vibrations. Weighing 300-600 tonnes, the 20 spans will be sequentially propped, cut free and moved by a special transporter to a nearby site. There they will be cut up and then trucked away for crushing.
While Liverpool’s Churchill Way failed its final test, “hundreds and hundreds of post-tensioned bridges have been standing in the U.K. since the 1990s and there’s nothing wrong with them,” says Stephen Collard-Jenkins, WSP technical director .