HS2 revealed yesterday (Monday 19 July) that its designers are making progress to reduce the amount of embedded carbon in one of the high-speed rail project’s viaducts by half.
Two steel girders will be firmly lodged between two layers of reinforced concrete to create a sturdy but light weight span. The ‘double composite’ approach will be used on the Wendover Dean Viaduct in Buckinghamshire.
Buckinghamshire Council approved the 450m viaduct under Schedule 17 of the HS2 act and it will be the first major railway viaduct in the UK to use the ‘double composite’ approach.
The viaduct was designed by HS2 Ltd.’s main works contractor, EKFB - a team made up of Eiffage, Kier, Ferrovial and BAM Nuttall - working with their design partner, ASC - a joint venture between Arcadis Setec and COWI - and specialist architects, Moxon.
It is one of 50 being built during the first phase of HS2 between London and the West Midlands.
Through the influence of the use of double composite structures on the latest French TGV lines, the British team has been able to lessen the amount of embedded carbon in the viaduct by 7,422 tonnes. The equivalent of 20,500 return flights from London to Edinburgh.
EKFB’s Technical Director, Janice McKenna, said “this viaduct was inspired by the latest innovative designs in France, but has been enhanced and developed in the context of the Chilterns. Our design solutions are always created with people and legacy in mind and I am really proud of the carbon savings that the Wendover Dean Viaduct represents.”
On top of significantly reducing the amount of concrete and steel - a major source of CO2 - the innovative design ensures local landscapes are taken into account, reducing the silhouette of the structure viewed from across the valley. In total, the steel weighs around 1,400 tonnes and will be covered with a concrete deck to carry the track and the built-in noise carriers.
Beams will be made from weathering steel, a material which will age to a dark auburn finish, echoing the natural qualities of the surrounding landscape.
HS2 Ltd.’s Project Client Director, Ambrose McGuire, said “by providing a cleaner, greener way to travel, HS2 will help cut the number of cars and lorries on our roads, cut demand for domestic flights, and help the fight against climate change.”
He added, “but we’re also serious about reducing the amount of carbon we use during construction, and Wendover Dean is a great example of how we’re using the latest engineering techniques to do just that. Concrete is one of the construction industries’ biggest sources of embedded carbon, and this design will help us cut our carbon footprint while delivering a lighter, stronger and more elegant structure.”
Nine strategically spaced piers – some of which will be up to 14 metres high - will be placed to reflect the near symmetry of the ground beneath, subsequently supporting the deck of the viaduct.
The structure will look much thinner as the pale concrete parapet will appear as a thin horizontal band hovering over the slender piers. This effect will be even more prominent as the viaduct piers - which have been lengthened, almost connecting with the parapet – will help ensure the appearance of a light and narrow structure.
In additional upgrades to the original design, and to reduce the amount of work on site, whilst minimising disruptions, the piers will be cast in pieces offsite before being assembled “like giant Lego blocks.”
The celebrated field boundaries and hedgerows will be refashioned following the construction of the viaduct, to ensure uninterrupted access for farmers and locals. A variety of shrubs and trees, typically found across the Chiltern chalk hills, will be used for new woodland planting - including Oak, Beech, Hazel and Wild Cherry - around the viaduct.