SCS Completes 14km HS2 Tunnel Breakthrough into Old Oak Common 2026

Key Points

• Skanska Costain Strabag (SCS) joint venture has successfully broken through into the Old Oak Common station box, completing a crucial 14km tunnel section.
• The breakthrough connects London’s future High Speed 2 (HS2) hub at Old Oak Common with the wider HS2 route extending to the West Ruislip portal on the capital’s north-western edge.
• Construction required the excavation of approximately 100,000 tonnes of London clay, which HS2 Ltd confirmed has been reused across other UK infrastructure projects.
• Traditional tunnel boring machines (TBMs) were impractical due to the narrowing track configuration, prompting engineers to use tunnel excavators for the 360-metre mined sections.
• The excavation process utilized a sprayed-concrete lining followed by cast-in-situ concrete finishing with travelling formwork.
• Engineers employed a unique breakthrough technique not previously used on HS2, cutting the tunnel’s dividing wall into blocks and pushing them out into the completed tunnel.
• Tunnelling works for this specific link originally commenced in May 2024 from the Victoria Road crossover box in north-west London.

Old Oak (North London News) November 4, 2026 — Engineers from the Skanska Costain Strabag (SCS) joint venture have achieved a major engineering breakthrough at Old Oak Common, completing the final stretch of a 14km tunnel network connecting the major station box to the northern HS2 mainline route.

How Was the Breakthrough at Old Oak Common Station Achieved?

The joint venture SCS successfully breached the concrete-lined station box at Old Oak Common following extensive underground works. The excavation process generated approximately 100,000 tonnes of London clay. According to official project details released by HS2 Ltd, the entirety of this excavated material was repurposed for environmental and construction schemes elsewhere across the United Kingdom.

The completion of this segment links what will serve as London’s central HS2 super-hub at Old Oak Common directly to the remainder of the high-speed line. This establishes a continuous subterranean route running directly to the West Ruislip tunnel portal situated on the capital’s north-western boundary.

Works on this specific tunnel segment originally initiated in May 2024, originating from a dedicated crossover box constructed at Victoria Road in north-west London.

Why Were Traditional Tunnel Boring Machines Not Used for This Section?

Engineers faced specific technical constraints that precluded the deployment of standard tunnel boring machines (TBMs) typically used across the HS2 project.

The primary challenge stemmed from a significant structural change in tunnel width along this specific passage. In this section, the high-speed rail line narrows from a two-track alignment down to a single track between the crossover area and the main station structure. This geometrical variation rendered giant TBMs impractical for the geometry of the dig.

Instead, the project team relied on specialized tunnel excavators to navigate the approximately 360-metre-long mined sections. To secure the subterranean structures, excavations were stabilized using a primary sprayed-concrete lining (SCL), which was subsequently reinforced with a permanent cast-in-situ concrete finish applied via heavy travelling formwork.

What Unique Engineering Methods Were Implemented During Construction?

The final breakthrough into the Old Oak Common station box—alongside the breakthrough of the corresponding northbound tunnel on 13 October—marked the first operational implementation of a novel construction process on the HS2 network.

To connect the mined tunnel to the station structure without compromising structural stability, engineers systematically cut the station tunnel’s dividing wall into massive individual blocks. Using specialist hydraulic equipment, the team pushed these blocks out from the station side back into the completed tunnel behind in a controlled manner described by project team members as a “Jenga-style” extraction method.

Background of the Old Oak Common and HS2 Development

The Old Oak Common site in West London is designed to be one of the largest and best-connected transport hubs in the United Kingdom. Serving as a crucial interchange, the station box itself spans over 850 metres in length and acts as the central hub connecting HS2 services with the Elizabeth Line, Great Western Railway national services, and local public transport infrastructure.

The SCS joint venture—comprising Skanska, Costain, and Strabag—is responsible for the primary civil engineering works along the southern section of the HS2 main line, including the complex 21km of tunnelling between West Ruislip and Euston. The subterranean works between Victoria Road Crossover Box and Old Oak Common represent a key logistical link within this civil engineering framework.

Throughout the excavation phases, project managers have focused on soil management and circular economy practices, diverting hundreds of thousands of tonnes of London clay away from landfills to support habitat restoration, land remediation, and structural fills across nationwide infrastructure projects.

Predictions: How Will This Breakthrough Affect Passengers and Transport Operators?

The completion of this continuous 14km tunnel link directly influences several key operational and commercial stakeholders across the UK transport sector:

1. HS2 Project Timeline and Civil Engineering Milestones

The structural connection into the station box enables rail systems teams to access the tunnel network earlier than previously scheduled. Track laying, overhead line electrification (OLE), and signalling installations can now proceed from the Victoria Road crossover box directly into the station site without logistical bottlenecks. This reduces potential delays for the commissioning phase of the London-to-West Midlands segment.

2. West London Regional Connectivity and Local Communities

With major heavy civil underground excavation wrapping up on this stretch, surface-level construction traffic, soil transport logistics, and localized environmental disturbances around North London and Ealing are expected to decline. For regional commuters, the structural progress brings Old Oak Common closer to becoming an operational interchange, which will eventually ease pressure on central London terminal stations like Paddington and Euston.

3. Rail Operators and Network Planning

For national rail operators—including Great Western Railway and Elizabeth Line services—the technical verification of Old Oak Common’s subterranean interfaces provides clarity for future timetable planning. The interchange will handle tens of thousands of transferring passengers daily once operational, altering passenger flow models across the capital’s existing rail network.