Background to specification
Following the flooding of Carlisle in 2005 and increased flood risk generally, the impact of the new Eden Bridge over the River Eden on its flood plain was a key issue to the construction of the Carlisle Northern Development Route (CNDR), the new 8.25 km road built west of Carlisle.
The local study carried out by the Environment Agency in the wake of the 2005 floods recommended lowering the floodbank downstream by 1 meter and removing an old railway embankment – mitigating the future threat to Carlisle but placing added importance on the Eden plain’s topography.
As a result of flood modelling work carried out by Capita Symonds, the technical adviser managing the project for Cumbria County Council, the plan for the new bridge’s northern embankment called for a series of culverts with a combined cross section of 160 m².
Although the illustrative drawing featured a concrete hatched structure, design engineers Scott Wilson recommended the greater practicality and easier installation of a corrugated steel system as manufactured by Tubosider UK, also the providers of the most economic solution.
“Tubosider’s bolted plate is Highways Agency approved, sufficient to gain approval,” says design manager Bob Gibson of Birse Civils, contractors for the design and construction of the new road. “It’s a system Birse Civils has often used before.
“Using their detailed plans for assembling each pre-fabricated component, all 15 culverts are now in place.”
Solution & benefits
The final solution was for 10 large diameter structures of 6mm thickness and then 5 smaller ones of 4mm, all ranging in span from 4.46 to 3.32 meters.
Opening in spring 2012, the CNDR runs from the A595 to M6 Junction 44 and is a £176 million public private partnership (PPP) concession contract run for Cumbria County Council by Balfour Beatty through its subsidiary Connect Roads.
It will take traffic away from Carlisle centre and improve links between West Cumbria, Scotland and the North East of England. As winning bidder, Balfour Beatty also takes control of 150km of existing road network and will maintain parts of the A7, A594, A595, A596, A689 and the A6071 for a period of 30 years.