Construction of the longest railway bridge in England has officially begun.
Construction of the UK’s longest railway bridge has begun in early 2021, and in spring of 2022, a 700 tonne machine was launched which is currently being used to lift giant concrete deck segments that form the viaduct, it’ll have lifted a total of one thousands of those deck segments by the end of the bridge construction, each weighing around 140 tonnes. An expert team of ground engineers have sunk the first of nearly 300 piles, which have formed the foundations for the Colne Valley Viaduct. The viaduct will be almost a kilometre longer than the Forth Rail Bridge, which will make it around 3.4km long, and carry trains going as fast as 200mph across lakes and waterways in northwest London. The design of the bridge was inspired by stones skipping on water, hence the elegant spans, some of which are as long as 80m, carrying the railway 10m above the surface of lakes, River Colne and Grand Union Canal.
About the bridge construction
The bridge will be supported by 56 piers, with the widest spans being located where the viaduct crosses the lakes, and the narrow ones near the approaches. Each of the piers will be installed by the bridge-building machine, also known as “Dominique”, named in memory of Bouygues engineer Dominique Droniou who played a leading role in its design and development. Each segment placed by the machine will have two half-arches attached on either side simultaneously to balance it, steel tensioning cables will also be threaded through the segments to strengthen the bridge. Every segment will have a slightly different shape depending on where it fits on the viaduct to ensure quality, safety and efficiency. Engineers from HS2 Ltd’s main works contractor Align JV – a team made up of Bouygues Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick – will construct 292 piles under the ground to support the viaduct piers in the next year. Each group of piles will have a concrete cap support, which will hold the full 6,000 tonne weight of the bridge. Holes will be bored before being backfilled to create each pile, and the main deck of the viaduct will be built in sections at a temporary factory, which produces around 12 segments every week, nearby before being assembled.
Easing your environmental concerns
The Colne Valley is a diverse countryside with parks, fields and reservoirs. It has many recreational spaces for visitors to enjoy, so the design was chosen in order to make it possible to see the landscape, minimize the impact the viaduct would have on the lakes and to compliment natural surroundings, as well as to ensure graceful aging. Sound cancelling barriers run all along the viaduct, in order to protect local neighbourhoods from train noise. HS2 has been working closely with Affinity Water and the Environment Agency for the past 6 years to monitor water quality and agree to working methods. A team of specialists will monitor the building site to ensure minimal damage to the natural environment. Pilling tests have been carried out at two locations, which resulted in engineers sinking 12 piles. The geological and structural data from these tests fed back into the design of the viaduct, which has resulted in a 10-15% reduction of depth of the piles and brought time and cost savings. Construction is expected to take two and a half years to complete. The trains for the railway will be up to 400m long and be able to carry over 1,000 people. It is planned to produce at least 54 of those trains.
