HS2 completes its first cut-and-cover green tunnel at Copthall

What happened

On 7 July 2026, HS2 Ltd revealed the completed Copthall tunnel at West Ruislip in west London — the first of the railway's cut-and-cover "green" tunnels to finish its civil works, and the project's only single-bore tunnel. The 880-metre structure was built by SCS, the joint venture of Skanska, Costain and STRABAG that holds HS2's main civils contract for the southern section. Work began in early 2021.

The headline is what went back on top. Around 1.2 million cubic metres of excavated material from the neighbouring Northolt twin-bore tunnel was reused to bury and landscape the structure, avoiding roughly 100,000 lorry movements on local roads.

Over the next two years the earth covering will be planted with trees, shrubs and other vegetation, after which the tunnel effectively disappears into the landscape. Rail minister Lord Peter Hendy said the tunnel "marks another significant milestone for HS2", crediting its design.

The technology

A cut-and-cover green tunnel is conceptually simple: dig a trench, build a box, bury it. But the execution at Copthall had some distinctive features. The tunnel is 12 metres high and up to 16 metres wide internally, sized for trains passing at up to 200mph, with five natural ventilation shafts up to 17 metres deep.

To form the structure's gentle curve, SCS used travelling formwork and falsework systems that advanced the pour 20 metres at a time, an assembly-line approach that avoids repeatedly erecting and striking temporary works.

The material strategy is the more transferable innovation. Rather than exporting spoil from Northolt's tunnel boring machines and importing fill, the programme treated one site's waste as the other's raw material, moving 1.2 million cubic metres internally. The works also required the permanent realignment of Harvil Road, rebuilt with a new bridge, and the tunnel sits in sequence between the Northolt tunnel and the Colne Valley viaduct on the approach to London.

Why it matters for UK & Ireland

Excavated material is one of the largest hidden flows in infrastructure. On a megaproject, spoil disposal drives cost, embodied carbon and, most visibly to the public, lorry traffic through communities that see years of disruption before any benefit.

Copthall demonstrates, at full scale and on the UK's most scrutinised project, that mass-balance planning between adjacent work sites can remove six-figure lorry counts from local roads. That evidence lands as the UK pipeline fills with earthworks-heavy road, rail and energy schemes, and as Ireland plans its own major linear projects, where spoil logistics through and around Dublin will be a defining constraint.

Green tunnels themselves are also a political technology. HS2's cut-and-cover sections exist largely to reconcile a high-speed railway with the landscapes and communities it crosses. A completed, planted example gives future promoters something concrete to point to when negotiating consent — and gives estimators real cost data rather than renders.

What to watch

Copthall is described by HS2 as its first completed green tunnel, with others still to follow elsewhere on the route; their pace will show whether the travelling-formwork method delivers repeatable productivity gains. The planting programme runs for two years, and the ecological performance of the restored surface will determine how persuasive the "green" label proves.

The larger question is institutional: whether HS2's spoil-reuse accounting — 1.2 million cubic metres retained, 100,000 lorry movements avoided, becomes a standard benchmark in UK and Irish environmental statements, turning what was an HS2 mitigation into a baseline expectation for the next generation of projects. One caveat: HS2's published material describes the completed structure and its material reuse; claims elsewhere that the tunnel replaced an originally planned open cutting are not detailed in the release itself.