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A new phase in the construction of the Mersey Gateway Bridge has started.
Three marine barges which includes the 410ft Harry McGill tower crane barge, arrived in the estuary in convoy after travelling up the River Mersey from the Liverpool Docks.
The barges are being used to build temporary structures known as cofferdams, to enable work to begin on the construction of the pylons that will support the three towers of the 1,000m long cable-stay bridge.
Cofferdams create temporary watertight enclosures in bodies of water when construction needs to take place below water level. Merseylink is installing three cofferdams in the estuary – one for each bridge pylon – with work already underway on the south cofferdam.
The work involves driving steel sheet piles into the riverbed to form two circular enclosed spaces: an outer circle of 40m in diameter and an inner circle of 20m in diameter. Approximately 300 steel piles will be used for each cofferdam: around 200 for the outer circle and 100 for the inner circle.
Once built, water will be pumped out and the outer areas infilled with local natural materials, such as stone or sand, to create a dry environment. This will allow workers to access the site and begin the necessary excavation and construction works.
It is expected to take around 30 days to build each of the three cofferdams. They will be visible in the river for the duration of the three-and-a-half-year construction project and removed once the work is complete.
(CD/JP)
