How the huge centrepiece will be raised

Giant hinges have been used to attach each leg of the pylon to the tusks that are built into the riverbed foundations to support the pylon.

The hinges are fixed together to hold the pylon in place and will enable the pylon to be rotated into a vertical position.

The backmast – a 50-metre high yellow, crane boom has been temporarily fixed to the pylon for the raising operation. It is being used to create an angle between the cables and the top of the pylon, which will allow the pylon to be pulled upwards.

The crane boom has been taken from Sarens’ SGC-120 super crane, affectionately named ‘Big Benny’, which is one of the largest cranes in the world, with a lifting capacity of 3,200 tonnes.

The cables used to pull the pylon into position – also known as strands – are connected to a blue spreader beam, which in turn is connected to the top of the pylon. They pass through four hydraulic strand jacks, anchored 30m into the ground on the south side of the river.

The cables are drawn through the jacks in order to pull the pylon into a vertical position.

As the pylon approaches its final position, the backmast will be retracted to stand vertically alongside the pylon and the north side cables will be tensioned to ensure the pylon is supported from both sides until it is fully secured. Once the raising is complete, the backmast will gradually be removed and lowered to the ground and work will begin to secure the pylon permanently to the tusks.

It will take three weeks of intensive work to ensure the pylon is fixed in place.

Each leg of the pylon will be fixed to one of the tusks with 20 bolts, with each bolt measuring 6m long by 65mm in diameter. A total of 40 bolts will secure the pylon in position.

After the bolts are fitted, tensioned and the gaps grouted, the base of each leg of the pylon will be filled with reinforced concrete. When all of that is complete, the rigging and cables used for the raising will be released.

The pylon will then become free-standing until the bridge deck is launched into place in thespringandthecablestays connecting the bridge deck to the pylon are positioned and secured over the summer.