HS2: Burton Green cut and cover tunnel pushes forward

The tunnel was designed by the Mott MacDonald Systra design joint venture (MMSDJV) on behalf of Balfour Beatty Vinci (BBV) – HS2’s main contractor for the West Midlands. It is being built by BBV.

In the last year, the team has constructed the southern portal entrance and carried out a series of underground structural elements, such as constructing retaining walls and installing more than 1,300 piles using 33,000m³ of concrete.

Work to build the 700m long Burton Green tunnel has now reached the halfway mark.

Once completed, the “green” tunnel will be hidden from view, with the roof covered with landscape planting and new footpaths to integrate the railway into the surrounding landscape.

To construct the 7m wide and 9m tall tunnel, BBV first builds retaining walls and then casts the roof slab on top of them. The tunnel is then excavated from ground level down to track level, as part of the "top down" construction sequence.

The internal base slab, dividing wall and walkway structures are then built in situ. Finally, the openings through the roof slab are infilled and the tunnel is filled over the top.

The retaining walls are 16m deep, with around 9m above track level and 7m below track level.

There will be around 60,000m³ of material excavated from within the tunnel, in addition to 70,000m³ excavated from the retaining structure section. The material will all be reused elsewhere on the project, such as to help create embankments.

Around 120,000m³ of fill material sourced locally from the wider project and transported via haul roads will be used on top of the completed tunnel as part of the landscaping process.

The material placed on top of the tunnel can be of a lesser quality as it is not required for a structural function.

For the retaining structures, a spokesperson for HS2 Ltd said that diaphragm walls (D-walls) were the preferred construction method “mainly due to the higher water table through this section”.

They explained that “the retaining structure walls are part D-wall, where the water table is higher, and part secant wall, where the water table is lower".

The spokesperson also noted that “logistics” and the “safe and timely” delivery of building materials was a key consideration on the Burton Green tunnel site.

“Specifically at Burton Green tunnel, we also need to carefully plan our programme of works within a long thin corridor of available workspace,” they said.

“Another key factor throughout delivery has been maintaining road connectivity for the Burton Green village by keeping the nearby Cromwell Lane open whilst safely building the ‘cover and cut’ tunnel beneath it.”

The Burton Green tunnel was granted planning permission by Solihull Metropolitan Borough Council in March 2024.

It is part of BBV’s 90km section on HS2 that stretches from Long Itchington in Warwickshire to the centre of Birmingham and on to Staffordshire.

The tunnel will carry HS2 trains through the village of Burton Green, near Kenilworth.

An onsite team of 150 people will now focus on the next phase of the build ahead of full completion in autumn 2026.

In addition to Burton Green, green tunnels will be constructed at Copthall in Hillingdon, Wendover in Buckinghamshire, and Chipping Warden and Greatworth, both in Northamptonshire.

In related news, HS2 construction progress in the West Midlands has seen work start on the 2,000 piles that will support the flagship Birmingham Curzon Street station, as well as the beginning of foundation work for a new bridge designed to carry HS2 trains under a section of the A38 near Lichfield.