Structural engineers from across the UK were being rushed to Cumbria this week as the local highways authority battled to inspect 1,800 bridges following extreme floods.
Network Rail, the Highways Agency and the Royal Engineers have been assisting with inspections and an additional 65 engineers were expected to arrive in the area as NCE went to press.
“Capita Symonds is organising bridge checks and has redeployed some staff [from around the country],” said Cumbria County Council highways network manager John Robinson. Capita Symonds has been working on Cumbrian highways for the last 10 years.
“Preliminary checks assess which bridges are affected and which ones aren’t,” said Robinson.
“Preliminary checks assess which bridges are affected and which ones aren’t.”
John Robinson, Cumbria County Council
Six bridges have already collapsed and many more remain closed while urgent structural checks take place. Most of the collapsed bridges were masonry arch bridges − some over 100 years old − in the area of Workington and Cockermouth.
Northside Road Bridge at Workington was the first to be swept away in the early hours of Saturday 21 November resulting in the death of PC Bill Barker.
By the end of Saturday five more bridges − Northside Footbridge in Workington, Lorton bridge near Cockermouth, Newlands Beck Bridge near Keswick, Camerton Footbridge linking Great Clifton with Camerton and the suspension footbridge over River Eamont near Dalemain − had collapsed.
Too much movement
“Masonry arch bridges don’t like being disturbed,” said Capita Symonds structural engineer Kenny Brooks, who has been assessing much of the damage over the weekend. “They rely on compression and when something moves, the cracking causes distress. They are strong when in place but not adaptable to movement. Modern bridges are more flexible. They still fail, but it’s less dramatic.”
Local authority engineers’ body CSS’s bridges group chairman Mike Winter who is also Dorset County Council’s head of engineering agreed that the strain on the bridges was excessive when exposed to extreme flooding.
“Bridges are designed to take loads from above. But the water must have caused immense horizontal forces below,” he said.
“Bridges are designed to take loads from above. But the water must have caused immense horizontal forces below.”
Mike Winter, local authority engineers’ body CSS
Brooks confirmed that it was the sheer weight of the water as well as scour which caused the larger road bridges to be swept away. Debris in the flood waters helped cause the collapse of the smaller pedestrian bridges.
“With some of the footbridges, it’s the weight of the water and the debris,” said Brookes. “[It seems] the foundations are still in place, but the deck has gone. Decks have been pushed off the supports.”
Workington’s Calva Bridge on the A596, has been severely affected by the floods. Its condition is being monitored by Balfour Beatty which manages that stretch of highway as part of the Connect consortium.
“There is no doubt the integrity has been compromised,” said Connect general manager Andy Dean. “One of the piers of the masonry arch is sinking.
“It’s moved so significantly that it’s caused structural cracking under the arch. We’ve not lost too much stone at the moment, but it’s still going down.” A full inspection will only be possible when water levels recede.
of rain fell in 24hrs on the fells in Seathwaite
Average daily rainfall for Cumbria in November
Depth of water in Cockermouth town centre during peak
Bridges being inspected in Cumbria
Collapsed or closed in this area