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TROUBLED

14th October 2004
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Which of the following most accurately describes the problem?

BRIDGE

M6's Theiwall Viaduct reopens next spring after three years essential repair work". But why was it needed and what has been done to sort the problems out? Kevin Swallow reports

Radio Two's Sally Traffic has helped to turn Thelwall Viaduct into a nationwide institution. Every day drivers phone in to report mounting congestion on the approach to the roadworks that cover the bridge.

And it hasn't done the government's Highways Agency any favours that frustrated truck and van drivers haven't spotted one hard hat or high-visibility jacket wandering about trying to look busy. So why bother closing it? In fairness to the Highways Agency, and project team leader David Brindle, there is no secret about what's happening. "We are replacing all the roller bearings under the bridge," he says.

It even says so beside the motorway — once you have been over Thelwall Viaduct, But why is the Highways Agency carrying out "essential repair work" that should not have been needed until at least 2010,in theory?

The original ThelwallViaduct was built by construction company Fairclough and opened in July 1963, designed to carry 16,000 vehicles a day. It became the third stretch of motorway to open after the MI and the Preston bypass.

By the early 1990s, increased traffic volumes meant improvements were needed.A new structure was put in place by Amec (the amalgamation of William Press and original bridge builder Fairclough) adjacent to the original, in 1995.The traffic was transferred to the new bridge (it's the one carrying all the traffic today) while the original was refurbished during 1996.The Highways Agency decided it wasn't cost-effective to tear it down and start afresh.Amec won the contract to rebuild it, reduced expansion joints (which allows the bridge to contract and expand) to four, and half joints (allowing the middle section over the water to sit between the approach sections) to two.

It turned the original viaduct into a three-section bridge, joining the separate carriageways into one for northbound traffic to use four lanes. Overall, it would be easier and cheaper to maintain, said the Highways Agency For six years it happily co-existed with the new bridge, delivering northbound traffic safely across the Manchester Ship Canal and the River Mersey. All 58.500 tonnes of concrete,steel and asphalt, stretched over 1.4km working as one to let 160,000 vehicles cross every day.

Then, in July 2002,a routine bridge inspection by the Babtie Group 2002 discovered a huge chunk of steel where it shouldn't have been.A 340x700mrn steel roller bearing, one of the biggest on the bridge, helping to support the section over the canal, had snapped in half. Brindle reveals that more than 800 tonnes was ■ supported on a knife-edge of what was left of the bearing still— but only just — in place.

If the bridge had moved enough to let the bearing roll over, the damage to the bridge would have been catastrophic.The motorway was closed within hours.The timing couldn't have been worse, with the Manchester Commonwealth Games about to begin. Since then only one lane, taking traffic northbound, has ever travelled across it and in February that was restricted to J21 for Warrington.

After discovery of the broken bearing at Pier V. further investigations discovered another two of the eight on Pier V cracked. As a precaution all were replaced.That initial work was scheduled to take until Christmas 2002 but further ultrasound tests found another eight roller beams, randomly located, had "failed". Further tests revealed the full extent of the problem — all the remaining 117 roller bearings had to be replaced, as most would not have made it past March 2001

Essential repair work

Each of the 36 piers that holds the bridge up has eight bearings, the outer two on either side are rocker bearings that have sufficient shelf life, are enclosed and will remain.The four roller bearings across the middle of the bridge, which were left exposed, are the ones being replaced.This is the "essential repair work" that is costing the British taxpayer £53m — a figure that includes .£6m strengthening work and traffic management.

There are wages for more than 190 people working on site, which is operating around the clock. and 70 on associated sites across the country.The scaffolding alone stretches more than 780km— the equivalent of Land's End to John o' Groats.

Brindle points out that the initial replace ment of eight bearings at Pier V was seen as an isolated incident which spiralled put of control. The lesson of the experience is about procedures — the need to make sure critical components have an adequate risk-based assessment. "If I've learned anything, it's to be aware of the unexpected.The failure was unprecedented. Never take anything for granted," he says.

The implications surrounding the original design are delicate and not up for discussion, pending a negotiated solution or potential legal proceedings. Instead of apportioning blame we look to see how the problem, under the guidance of John Martin Construction's contracts manager Pete Wilkinson (with Jeff Sharpe, the Atkins site project manager who designs and oversees the works) is being rectified.

Derbyshire native Wilkinson has lived and breathed the Thelwall Viaduct since the repair work started, so much so he has a caravan on site. Both he and fishing fanatic Sharpe explain what is going on.

At Pier V. stiffeners were inserted each side of the main vertical support beam where the initial broken roller-bearing was discovered, allowing the engineers to push up the bridge with two 400-tonne jacks. They then replaced the failed bearing with a new sliding spherical bearing (SSB) made from aluminium.

Because the bridge is unique, new techniques were needed to sort out the other bearings, inserting stiffeners and lifting wasn't an option all the way around. Wilkinson came up with an A-frame that is drilled and bolted to the main vertical support beam at the top.This worked—to a point — then a third option was

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needed. The third, and most often used design, is the one widely seen on the Highways Agency website. Brackets are attached either side of the vertical support beam and four jacks lift the bridge 0.2mm to allow the workers to remove the old roller bearing and replace it with an SSB. Not much room to work with, admits Wilkinson with a wry chuckle.

Each four-man gang takes approximately 10 days to remove the original bearing and replace it with the new before moving on to the next. His team has had to work its way through the problems. developing techniques and engineering as it goes, but there is little it can do about nesting endangered species like kestrels.Two sets of nesting kestrels, one on the Lyrrirn side of the canal and the other on the Mersey side, were discovered in February and work on those two sections of bridge was abandoned until they left of their own accord.

Work was held up but the engineers were able to work around them on adjacent piers, so even though they nested for three months no real time was lost. In all, nine chicks were hatched. Repair work also had to wait on continuous checks for greater crested newts that live in the conservation area around the canal and river. Wilkinson believes the approach to such a unique bridge has required everyone involved to push in the same direction He is at pains to point out that the culture for suggestion wasn't there before,but this was still very much a team effort.

-Partnering is the best way to go. Previously, it would be us in one corner and the Highways Agency in the other and we'd lock horns over how to sort out the problems," he says.

"Engineers can come forward, and because they are the ones doing the work, their views are as important as the site manager." The main lesson is that with an open floor policy, it gives everyone the right to suggest potential answers to the problems facing them— even unexpected ones like the Thelwall Viaduct.

Currently more than half the roller bearings have been replaced. Further strengthening work is scheduled, and road resurfacing, before its estimated re-opening in spring 2005. •

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CONTACT Further updates are available on: vvww.highway.gov.uk


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