THE iconic £1.86 billion Mersey Gateway is taking shape.

Construction teams have begun to build the three giant pylons that will support the new bridge.

These pictures show the gargantuan task of filling the massive cofferdams with concrete.

The intricate procedure involves pumping 1,400 cubic metres non-stop for around 24 hours.

The three pylon foundations will sit below the riverbed and will each measure 4.5 metres high and up to 22 metres in diameter.

Before this, a concrete base layer is built on floor of each cofferdam.

A cage made of steel reinforcing bars is then assembled and encased in steel matting.

A working platform is also installed to provide access for site workers.

Upright steel reinforcement bars are then fixed into the centre of the cage to form the beginnings of the pylon shaft.

This is the tall structure that will rise out of the riverbed to support the bridge deck.

Once the assembly work is finished the concrete pour can begin.

Merseylink’s site agent, George Houston, said: “This is one of the biggest concrete pours that I’ve ever been involved with.

“We’re using a massive amount of concrete, over 600 truckloads just for the three pylon foundations.

“It’s an extremely technical part of the project and our teams will be working round the clock to get the job done.”

Altogether, around 127,000 cubic metres of concrete will be used for the entire project.

That’s the equivalent of around 20,000 truck mixer loads of concrete.

Matthew Fleetwood, Merseylink’s senior materials engineer, said: “It’s a bit like baking a cake.

”We have to get the ingredients for the mixture exactly right.

“The concrete needs to be extremely strong and durable, given the size and scale of the bridge and the environmental factors of the estuary.”

As each pylon foundation is completed, work will begin on the pylon shafts.

A metal mould known as formwork will be lifted into place by a crane and attached to the pylon foundation for the concrete to be poured into.

The formwork will move up the pylon shaft allowing the pylon to grow. It is estimated that each section of the shaft will take around five days to build.

The three pylons which will rise out of the riverbed to support the bridge deck should begin to be visible in the estuary from September, 2015.

Hugh O’Connor, general manager of Merseylink, said: “Starting work on the bridge pylons marks another significant step for this important infrastructure project.

“Work is progressing at pace now on all sections of the site and a huge amount of activity will be taking place over the next few months.”

Halton Council leader Rob Polhill, chairman of the Mersey Gateway Crossings Board, said: “This is an important time for Halton.

“What we are seeing really is history in the making and we have a lot to look forward to in the future.

“Every construction milestone brings our new bridge one step closer. It’s going to be exciting to see the bridge pylons form in the estuary and I, for one, will be watching with interest.”

The new bridge is due to open in 2017.