HS2 has announced the latest stage of progress on a ‘green tunnel’ at Wendover in Buckinghamshire.
This week has seen the completion of the central part of the cut-and-cover structure, which has been designed specifically to cut noise and disturbance for those living nearby.
Set to measure in at roughly 1 mile (1.4km); the tunnel is being built inside a cutting alongside the A413 to the west of the town and, once each section is complete, earth is being replaced in order to blend the railway into the surrounding countryside.
Wendover’s green tunnel has been assembled from 2740 precast concrete segments, and takes the form of an ‘M’ shape, with separate halves for northbound and southbound trains.
In a bid to speed up construction, the tunnel has been built in two sections to allow for excavation, preparatory work, construction and backfilling to happen at different points simultaneously. These two halves met this week, with the final segment slotted into place on Monday 5 October.
Teams marked the achievement by signing their names on the segment before it was lifted into position and, with the central portion of the tunnel now complete, focus will turn to the portals at either end, completing the floor slab and the internal fitout process.
Ellesborough Road – which runs from the town in the direction of Princes Risborough – is currently carried over the construction site on a temporary bridge, with the final stage of construction set to see it realigned over the top of the tunnel in order to complete the landscaping.
HS2 Ltd’s Project Manager, Umesh Gorasia said:It’s great to see the two halves of the tunnel linked up for the first time. Once complete, the green tunnel will dramatically reduce disruption from passing trains and blend the railway into the countryside.
There’s still some way to go, but we’re making good progress and I’d like to thank the team for all their hard work.
Construction work on the tunnel is being handled by EKFB, HS2’s main works contractor responsible for the central section of the route through Buckinghamshire and into South Warwickshire. EKFB is a joint venture made up of Eiffage, Kier, Ferrovial Construction and Bam Nuttall.
In total, over 1.2 million cubic metres of material – mainly chalk – was excavated to form the level base for the tunnel. Whilst this was stored on site, it is now being backfilled and compressed in order to ensure that the weight is spread equally across the structure.
Once completed, HS2 will utilise a set of five ‘green tunnels’ between London and Birmingham, with the project’s Copthall tunnel recently completed on the outskirts of the capital earlier this summer.
Wendover is one of three green tunnels being built by EKFB, and the company has stated that lessons learnt shared between the different teams to help improve productivity and speed up construction. This includes pre-fabricating, reinforcement cages for the base slab, improving the delivery of concrete through the tunnels and testing to safely increase the size of machinery backfilling the tunnel.
Although the majority of segments were lifted with a crane, the ones installed under the Ellesborough Road temporary bridge were lifted into position using a specialised piece of equipment called a self-propelled modular transporter (SPMT). Supported by 16 sets of wheels, the machine allows engineers to lift the beams from underneath before placing them into position beneath the bridge.
In total, roughly 65 miles (105km) of tunnels will be built between London and the West Midlands, and 130 million tonnes of earth will be excavated. The majority of these will be deep-bored tunnels, whilst five will be more shallow, cut-and-cover tunnels – like the one at Wendover. These will be at Chipping Warden, Greatworth and Burton Green and the Copthall tunnel in Hillingdon.
