The 270-tonne machines operate in a similar way to the Movable Scaffold System (MSS) that is building the elevated approach viaducts. They were assembled at the south pylon earlier this year before being lifted to their starting position around 25 metres above the riverbed. The construction team then cast a pier table – a rectangular shaped platform – around the bridge pylon before preparing to start work on the main bridge deck.
The construction joint venture for the £600m Mersey Gateway Project is made up of Kier Infrastructure & Overseas, Samsung C&T Corporation and FCC Construcción. They are working for the Merseylink Consortium, which is owned by Macquarie Capital Group, Bilfinger Project Investments Europe and FCC Construcción.
Kyuyoung Choi, Merseylink’s operations manager for the main crossing, explained the building process: “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.”
The form travellers were designed and built specifically for the Mersey Gateway Project. When the bridge is complete, the machines will be dismantled and recycled.
Three pairs of form travellers are being used to build the bridge deck with each pair operating as a unit. The machines will be launched from the north pylon later this month (September 2016) and from the central pylon during October.
Work on the bridge deck is expected to finish in summer 2017. During this time the form travellers will have cast a total of 154 deck segments between them. Each segment of deck will be around 33 metres wide and 6 metres long and will take around a week to construct.
The largest number of deck segments will be cast from the south pylon. There will be 33 segments between the south pylon and the south elevated approach viaduct, and 31 cast from the south pylon towards the central pylon.
The north pylon will see 29 deck segments cast on one side and 27 on the other, while 17 will be cast from either side of the central pylon.
Merseylink general manager Hugh O’Connor said: “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. Technically, it’s a very challenging process and this is where the international expertise from our highly skilled engineers will be invaluable, with many having worked on similar projects around the world.”
The new bridge is on schedule to open in autumn 2017.