Two specially constructed giant bridge building machines have started work on the £1.9bn Mersey Gateway, enabling construction of the 1,000m reinforced concrete bridge deck.
The bespoke 270t form traveller machines are two of six that are working on the new river crossing at Halton, with the construction using the machines in three pairs. They moved apart for the first time at the south pylon last week.
Working as movable concrete moulds, the machines work at a level of 25m above the river bed. The machines will construct a total of 154 deck segments, each around 33m wide and 6m long, and taking a week to build.
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.
The Merseylink Construction Joint Venture is led by Kier. The £1.86bn cost includes maintenance and operations until 2044.
“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,” said Kyuyoung Choi, the Main Crossing’s operations manager.
“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.”
“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,” said Merseylink general manager Hugh O’Connor.
“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.”
Work on the bridge deck is expected to finish in summer 2017. The new bridge is scheduled to open in autumn 2017.