A YEAR after the launch of HS2’s giant bridge-building machine, progress on the UK’s longest railway bridge has taken another major step forward.

The first piers, which will carry the viaduct over a series of lakes, are complete. .

The Colne Valley Viaduct – which is being built near Hillingdon - will carry high-speed trains more than two miles across the Grand Union Canal, River Colne, roads and a lakes between the end of the London tunnels and the start of the Chiltern tunnels.

For the last year, a 700-ton ‘launch girder’ – the only one of its kind in the UK - has been assembling giant pre-cast concrete segments to form the first kilometre of the viaduct deck along the edge of the valley.

The first enormous V-shaped piers have now been completed in the lake, to allow the viaduct to curve eastward, over the water.

The V piers – each weighing in at 1,800 tons – will support a row of arches inspired by the flight of a stone skimming over the surface of the water.

To allow for the gentle curve of the viaduct, each of the one thousand segments that form the arches and deck are slightly different.

All are manufactured at a temporary factory set up close by, with direct access to the M25.

In the last year, the launching girder has installed more than 300 out of 1,000 segments required to complete the viaduct deck.