Project Overview

Joseph Gallagher Ltd was appointed as Shaft Sinking Contractor on the Mandeville Road Ventilation and Intervention Shaft, a key part of the HS2 Northolt Tunnels programme in northwest London. Working as a specialist subcontractor to the Skanska Costain STRABAG Joint Venture (SCS JV), the project formed a critical element of the high-speed rail network’s safety, ventilation and emergency access infrastructure.

The Mandeville Road shaft is one of four major ventilation and intervention shafts constructed at approximately 3km intervals along the Northolt Tunnel alignment. These shafts play a vital role in regulating air quality and temperature within the tunnels, while also providing permanent emergency access points.

At 20 metres in diameter, the Mandeville Road shaft was the final precast concrete segmental shaft delivered as part of this phase of the HS2 works.

Project Challenges

The project presented several engineering and logistical challenges, including:

Constrained site conditions on a steep embankment adjacent to the London Underground Central Line
A residential urban environment, requiring careful control of noise, traffic and deliveries
The former use of the site as an old Affinity Water pumping station
The need to minimise environmental impact and overall construction footprint

Given these constraints, a range of shaft construction options were considered during the design stage. The requirement for a compact footprint and efficient construction programme ultimately led to the selection of a precast concrete segmental shaft sunk using the underpinning method.

Our Solution

Joseph Gallagher Ltd successfully delivered the shaft using the underpinning method of construction, a technique in which shaft rings are sequentially installed as excavation progresses beneath them. This approach is widely recognised as structurally robust, highly efficient and well-suited to restricted urban environments.

The Mandeville Road shaft comprised 12 precast concrete rings, each forming part of a 20m-diameter structure supplied by FP McCann. From installation of the first ring, the shaft sinking operation progressed uninterrupted, demonstrating the reliability of both the design and the construction process.

Our team worked closely with the SCS JV and supply chain partners to coordinate just-in-time delivery of the precast segments. This approach significantly reduced on-site storage requirements and helped to limit traffic disruption in the surrounding residential area.

Environmental and Community Considerations

Environmental performance was a key consideration throughout the project. The selected shaft construction method offered several sustainability benefits, including:

Reduced excavation volumes compared with alternative shaft solutions
Lower associated material handling and spoil removal, helping to reduce the project’s carbon footprint
A smaller site footprint, minimising disruption to the local environment

Careful logistics planning and sequencing ensured minimal impact on local residents, while maintaining safety and programme certainty.

Engineering Excellence

The precast shaft segments were manufactured with integrated EPDM rubber gaskets, providing an immediate watertight seal upon installation. Segment connections were designed to ensure full gasket compression, delivering long-term durability and performance in demanding ground conditions. By combining high-quality precast components with proven shaft sinking techniques, Joseph Gallagher Ltd delivered a solution that met the project’s structural, environmental and operational requirements.

Project Outcome

Shaft sinking at Mandeville Road progressed efficiently and safely, meeting programme expectations and maintaining excellent standards of quality throughout. On completion, the shaft will be topped with an integrated above-ground headhouse, housing fire control and tunnel ventilation systems to support the safe operation of HS2.