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Curved beams help to raise new Mersey Gateway Bridge pylons

28 June 2016

The project to build a new bridge across the River Mersey is well underway, with work already started at the sites for the three main bridge pylons.

In order to have a safe environment in which to build the foundations, engineers have constructed a series of cofferdams with the help of Barnshaws metal benders, which has supplied nearly 400,000kg of curved, heavy section steel for Bolton – based contractor, SPI Appleton Limited.

The cable-stayed bridge design will have a total span of 1,000 metres spanning the river Mersey and the Manchester Ship Canal, the main bridge deck will be supported by steel cables attached to three pylons that are being built in the Mersey estuary. The finished crossing will provide three lanes in each direction, linking the Central Expressway in Runcorn with the main routes to the M62 and towards Liverpool.

For any major construction project, getting the foundations right is a crucial aspect but when they are to be in the middle of the River Mersey that can be easier said than done. The first step is actually getting to the locations and setting up a working platform that can support all of the equipment required to build the bridge pylons.

In this case a 1,000 metre long trestle causeway is providing temporary access to the locations of the three supporting pylons allowing the cranes and pile drivers to complete construction of the cofferdams. These create watertight enclosures allowing the engineers to work safely below the water level of the River Mersey.

The work to create the cofferdams involved driving steel sheet piles into the riverbed to form an outer circle with a diameter of 40m and a second, inner circle with a 20m diameter. Now these are in place the water has been pumped out and the space between the two sets of steel piles filled in with local natural materials to form a dry refuge in the centre.

However, before the infill material could be added, the steel piles needed to have some reinforcement fitted so that they can cope with the additional pressure. This came in the form of huge steel sections that have to be strong enough to support the piles and curved to match the radius of the inner circle.

The task of creating these enormous curved sections was awarded to Barnshaws Metal Bending, which is renowned for having the tools and knowledge to deal with the largest of projects. The steel sections measure up to 356 x 406mm and weigh 467kg/m and they are formed to a radius of 9.7m so as to fit on the inside of the steel pile structure.

Greg North, Commercial Director at Barnshaws, comments: “As the world’s largest metal bending company, we are extremely competitive when it comes to this type of challenge. We often work on large structural steel sections, bending them to add strength to a structure, improve the aesthetic qualities of a project, or, in this case to fit a precise curved profile. In all, we have formed nearly 400,000kg of this heavy duty steel section to the exact requirements of the client. They will provide the strength necessary to hold the shape of the cofferdams while the foundations of this new river crossing are constructed.”

The new Mersey Gateway Bridge is due to open in 2017.

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