HS2 has confirmed that it is on track to cut the amount of embedded carbon
in the Colne Valley Viaduct by at least 28.4%, as works continue for what will
be the UK’s longest railway bridge.
Applying lessons from the construction of the latest European high speed
railway bridges, the British team has cut the amount of embedded carbon in the
viaduct by 63,300 tonnes CO2e – the equivalent of 234,500 flights from London
to Edinburgh.
The production of concrete and steel are major sources of CO2 emissions, so
narrowing the width of the viaduct allowed a significant reduction in carbon,
and helps reduce disruption for local residents by reducing the number of HGVs
on local roads.
Inspired by the flight of a stone skimming over the surface of the water,
the Colne Valley Viaduct will stretch for 3.4km across a series of lakes on the
outskirts of London, and will be one of the most high-profile structures on the
new HS2 high speed rail link under construction between London, the West
Midlands and Crewe.
HS2 Ltd’s main works contractor Align JV – a team made up of Bouygues
Travaux Publics, Sir Robert McAlpine, and VolkerFitzpatrick – worked for four
years on the design with architects Grimshaw and design partners Jacobs and
Ingerop-Rendel.
Starting from the reference design produced as part of the HS2 parliamentary
process, they refined the design, challenged assumptions, and found
efficiencies to help reduce the amount of steel and concrete in the structure.
This included working closely with rail systems experts at HS2 Ltd to allow
the structure to be narrowed by over 1m, while still allowing sufficient space
for signalling and control equipment alongside the line. They also worked to
bring the northbound and southbound tracks closer together further north, which
in turn significantly reduced the amount of earthworks required for the
approach embankment.
Conscious of commitments made to the community about the appearance of the
viaduct as it passed over the lakes, the team focused on creating long graceful
arches over the water while reserving simpler, easier to construct, designs for
the approaches. Inside the viaduct, the engineers opted for a ‘post-tension’
design, with lightweight super-strong steel cables running the full length of
structure.
The cables will be monitored 24/7 by a network of high-tech sensors and act
to bind the viaduct together allowing it to handle the enormous forces produced
by trains passing at speeds of up to 200mph (320km/h). This combination of
steel and concrete allows for the most efficient use of the materials and the
low elegant profile of the viaduct.
Every element of the design was challenged during the design process, with
noise barriers moving from solid concrete to a composite design with noise
absorbing steel cassettes at the bottom and transparent acrylic at the top,
helping to reduce the amount of concrete while also reducing the visual weight
of the structure and enabling views across it.
An extensive programme of test piling was also completed ahead of the start
of construction with geological and structural data from these tests fed back
into the design of the viaduct. This has resulted in a 10-15% reduction in the
depth of the piles and associated time, cost and carbon savings.
Billy Ahluwalia, HS2 Ltd Senior
Project Manager, 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.
“But we’re also serious about
reducing the amount of carbon we use during construction, and the Colne Valley
Viaduct is a great example of how we’re using the latest engineering techniques
to do just that. Concrete is one of our 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.”
Alan Price, Align Design Director:
“In designing the viaduct we have had
to address the challenges of not only building a structure capable of handling
the huge forces that will be exerted on it from high speed trains operating in
both directions, but also to meet the demands of local stakeholders, creating a
design that not only makes a positive statement, demonstrating world class
engineering, but also really works within the environment in which it is
placed.
“Working through the design process and
using the original specimen design as a starting point, we have been able to
deliver not only an iconic design but also a significant reduction in CO2
required to build the viaduct. This is not only a significant achievement for
all those involved, but also for the environment.”
Construction began earlier this year, with the first of 292 concrete piles
sunk into the ground to form the foundations for the viaduct.
On top of each group of piles – some of which will go up to 55m into the
ground - a concrete pile cap will support each of the 56 piers which will in
turn support the full weight of the bridge structure above. Instead of
hammering the piles into the ground, holes are being bored before being
backfilled to create the pile.
Set low into the landscape, the piers will support a series of elegant
spans, some as long as 80m, which will carry the railway around 10m above the
surface of the lakes, River Colne and Grand Union Canal.
The main deck of the viaduct will be built in sections at a temporary
factory nearby before being assembled from north to south starting next year.
