Work Begins On UK’s Longest Rail Bridge

The first of 56 piers needed to support the UK’s longest viaduct has been completed, New Civil Engineer reports. The Colne Valley Viaduct (CVV) is being built as part of the HS2 project, and will be 3.4km (2.1 miles) long. It will run from the outskirts of Hillingdon, North West London, towards the Birmingham leg of the rail project.

The 56 reinforced concrete piers are 6m tall and weigh around 370 tonnes each, and the first one was cast on site by a team of specialist engineers. The piers will rest on concrete piles which are set 55 metres into the ground, and are designed to support the full weight of the deck.

The viaduct is routed across a lake, so the piles will be bored directly into the lakebed with the use of a cofferdam to hold back the water during the construction process. The engineers studied highspeed rail bridges in Europe to help them find ways of reducing the embedded carbon in the bridge.

Align project director Daniel Altier said: “I have no doubt that the viaduct will become one, if not the most striking element of HS2 phase 1 once complete. The way it will be constructed is going to be equally fascinating for engineers young and old.”

He added: “The sections for the deck will be fabricated at our main construction site to the west of London just inside the M25, and using a huge launching girder, the deck will be formed from north to south, along the line of the route, thereby keeping unnecessary construction traffic off the roads.”

Rail Engineer reports that the CVV lies within the Colne Valley Regional Park, which includes farmland, woodland, and reservoirs. In particular, Broadwater Lake is an environmentally important site, which is home to many aquatic birds. There has been some local opposition to the construction of the viaduct, which was taken into account by the designers.

The design has been kept deliberately slender, both to minimise the visual impact and the amount of embedded carbon in the bridge. Structurally, the bridge is described as a series of V-piers 80m apart, which “form a rhythmic sequence of low, slender arcs that skim lightly over the surface” for the parts which cross water.

The spans will be shorter through the woodland sections, with facetted concrete forms used to create pattern and texture. On each side of the track will be 1.65m of noise-absorbing panels, and 2m high self-cleaning acrylic panels will allow passengers to have a view from the train windows.

The project is expected to be completed in summer 2024, with the bridge fully operational by spring 2025. The main decks of the viaduct are being precast in sections at a nearby factory, that has been specially constructed for the purpose. The deck units will have a constant top-section, but they are variable in height and weight.

The architectural design was carried out by an integrated design team known as Align-D (Align, Jacobs and Ingérop), working with Grimshaw Architects. Sir Robert McAlpine and VolkerFitzpatrick are also involved in the project.

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