A major milestone has been reached on the £600 million Mersey Gateway Project in north-west England.

Two out of the six giant bridge building machines have now been launched, which will build the 1,000-metre long reinforced concrete bridge deck across the River Mersey.

Each 270-tonne machine operates in a similar way to the Movable Scaffold System (MSS) which is developing the elevated approach viaducts.

The form travellers were assembled at the south pylon earlier this year before being lifted to their starting position around 25 metres above the riverbed. Project teams then cast a pier table – a rectangular shaped platform – around the bridge pylon before preparing to start work on the main bridge deck.

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Three pairs of form travellers are being used to build the bridge deck and work is expected to finish in summer 2017.

Merseylink's Kyuyoung Choi, Operations Manager for the Main Crossing, said: "Each segment of the bridge deck is made in the same way. Reinforced steel is placed into the mould and we then pour around 130 cubic metres of concrete inside to create each segment.

"From the third segment onwards, we install the connection boxes, which are called 'delta frames', for the steel stay cables, which are then attached to the upper pylon. The form travellers, which are powered by a hydraulic system, then move forward on a set of rails to the next position and the process is repeated.

"The deck segments are cast simultaneously, which allows the bridge deck to ‘grow' from either side of the pylons until it meets the connecting bridge deck and the structure is complete."

Hugh O'Connor, General Manager of Merseylink, added: "This is going to be one of the most visually exciting parts of the project. As the structure of the main bridge begins to extend across the estuary it will completely transform the local landscape."

The overall Mersey Gateway Project is scheduled for completion by 2017.

(LM/CD)