Engineers have completed a critical operation to salvage the southern central pier of the Workington “Calva” bridge and bring it one step closer to long term survival.
The final concrete pour to has been completed and last week contractors moved on to the bridge to begin stripping off the deck to further check the integrity of the structure.
“As we progress this work confidence is rising that we can repair the bridge,” said Connect Roads regional manager Andy Dean. “We are on the positive side of 50:50 that the bridge can be saved. We will know for sure by the end of September.”
Connect Roads is the Balfour Beatty-led highway maintenance and construction firm that is responsible for the bridge.
Workington bridge became the high profile symbol of the Cumbria floods of November 2009. TV cameras camped on the banks of the river Derwent waiting for the bridge to collapse after its southern central pier was severely damaged.
At the time, the bridge was condemned but it stayed standing and results from subsequent structural analysis by the Balfour Beatty/Mouchel joint venture Scotland Transerv prompted Connect Roads to opt to attempt to repair the structure rather than knock it down and build another one (NCE 15 April).
The floods had caused the foundations of the pier to be eroded on its upstream side, forcing uneven distribution of the 1,000t dead load imposed on it.
“We had hoped to do just one pour but there was a huge hole that the river had scoured out”
The repair involved building a gravel causeway out to the pier and then two temporary piers were positioned on the damaged side. Jacks lifted the bridge up and transferred 300t of the load to the temporary piers to give the damaged pier some respite.
Connect Roads built up the flood hit pier in three pours. The first of 49m3 filled in the scour hole and created a foundation for the second pour of 24m³. This included installation of 11 permanent jacks loaded to an aggregated upthrust of 540t, which then took the weight of the bridge from the temporary piers. The temporary piers were removed before site workers completed the final pour of 4m³.
“We had hoped to do just one pour but once we’d created a cofferdam round the pier and pumped the water out there was a huge hole that the river had scoured out,” said Dean. “So we had to change the work method.”
Spring tides and heavy rain delayed work by two weeks.
“If all goes well we will know 100% if the bridge can be saved by the end of September and it could come back into service by early November. A replacement bridge would have taken two years to build,” Dean added.