Clément Chasset (CC) / I’ve spent a large part of my career abroad. First in Poland and then in the Ivory Coast, I arrived in England seven years ago. I contributed to projects such as Hinkley Point C, for which I was in charge of the installation of the concrete plants.

I’ve been working for Align and the HS2 project for five years. This joint venture, which is composed of Bouygues Travaux Publics, Sir Robert McAlpine and VolkerFitzpatrick, is in charge of the construction of the C1 (Central 1) section of the future high-speed railway line, from London to Birmingham (HS2 Phase 1). During the first stage, which is the development of the project design and the execution of the preparatory works, I was initially given various production tasks such as the launch of the geotechnical campaign (with analysis and samples) and the development of the first earthworks sequences. As we got closer to the start of the execution works (stage 2), I focused on the construction of the Colne Valley Viaduct. I’m now working as a Project Manager in charge of the infrastructure of this 3.4-kilometre-long viaduct. More specifically, this includes the construction of the temporary land access roads, the temporary bridge to cross lakes and rivers, as well as the temporary cofferdams. These cofferdams make it possible to carry out the part of the work that is below the water level, such as piles and foundations. I'm also in charge of permanent structures like piles, foundations, piers, and abutments. My job stops at the bridge’s abutments!

CC / One particular feature of the viaduct is the construction of V piers, also known as “Arch Form Deck” – piers shaped like arches. The curve of these piers was inspired by the flight of a stone skipping across the water… Beyond this poetic architectural nod, these piers are among the few visible parts of the structure. They truly are the visual signature of HS2 Phase 1.

Another specificity of the project is the variety of constraints. Most of them come from the infrastructure works, whether in the design phase or during the works phase and related to ecology or stakeholders like the local population.

The C1 section runs through a protected area. The tunnel section is located in the Chilterns, which is certified as an Area of Outstanding Natural Beauty (AONB), a protected area recognised for its scenic beauty – like a national park. The Colne Valley, the place where we’re building the viaduct, is a Site of Special Scientific Interest (SSSI), a protected area where specific regulations apply and have a direct impact on the construction process. The Production and Environmental teams are working closely with Natural England, an organisation that acts like the government’s adviser for the conservation of wildlife and nature. The impact of the works on local species and residents is measured on a daily basis and we have to adapt our work if necessary, ensuring the project is responsible and environmentally friendly.

We are also facing a technical challenge relating to loads the viaduct needs to handle that must support the passage and emergency braking of high-speed trains travelling at a speed of 380 km/h.

CC / The viaduct consists of a total of 56 piers and 292 piles. There are between four and six piles under each pier, some of which will reach 55 metres in depth. The cofferdam is then built to both retain the soil during earthworks and to prevent rise of water, as the groundwater is quite high in the area. In the end, each of these groups of concrete piles will support the piers, which themselves carry the bridge structure, a concrete deck.

The main deck of the viaduct is made up of 1,000 prefabricated segments, which are manufactured in a temporary factory located near the construction site. The viaduct construction starts at the north abutment and runs south through the Colne Valley. All of the deck segments, each of them weighing around 100 tonnes, are transported onto site by SPMTs (self-propelled modular trailers) and a launching girder will be used to put the segments in place. Once they’re in their final position, the segments are fixed and grouted to form the deck structure.


The next phases of this exceptional worksite

Work on the temporary jetties across the lakes in the Colne Valley is well underway as is the piling for the first piers to the north of the Colne Valley. Work on the ‘V piers’ will start in March next year.

Curious?

Clément tells you more on this video!

More details on the construction right here.