BLUEBAY SUPPLIES PRODUCTS FOR THE HS2 COPTHALL GREEN TUNNEL
The Copthall Green Tunnel is an impressive 880-metre tunnel being constructed by Skanska Costain STRABAG Joint Venture (SCS JV) as part of HS2. Located within the London Borough of Hillingdon, the tunnel sits between the twin-bored Northolt Tunnel and the Colne Valley Viaduct. It is one of five green tunnels on the HS2 route – shallower tunnels that will be finished with trees, plants, and shrubs on top, helping them blend into the natural landscape. Building on our longstanding experience on HS2, we’re supplying Bluebay products here, as Lucy Furnival explains.
It’s amazing to think of the places our products end up, with projects all over the country, including on HS2.
This particular focus is on the Copthall Green Tunnel. As one of five shallower green tunnels on the HS2 route, its ‘cut and cover’ design significantly reduced the movement of soil, and approximately 1.21 million cubic metres of excavated material were kept on site for reuse within the tunnel surroundings – ensuring a greener and better visual integration of the railway into the surrounding landscape.
SCS’s role on the project was to construct a rigid concrete box structure within a 20-metre-deep cutting, which ultimately formed the green tunnel for the HS2 trains. This was constructed using steel reinforcement and in-situ concrete to form the base, walls and roof of the structure. Civil engineers on the project, Kilnbridge, installed two products from Mapei – the Mapeproof AL AP system and the Mapeproof AL 1200 AP system to the base and walls – each provided by our team at Bluebay.
This followed comprehensive compliance testing, design input, and commercial and technical site support throughout all phases, provided by Bluebay and Mapei’s UK and international teams. Particular attention to detailing was vital – taking into account requirements for buildability, piles, joints, continuity and compatibility at interfaces, changing environmental conditions, and the need for long design life and minimal maintenance.
The tunnel specification included the Mapeproof AL AP System, a pre-applied, fully bonded, self-adhering HDPE waterproofing membrane, selected as the primary external tanking waterproofing system to receive the poured concrete for the tunnel slab. Cold-applied and requiring no heat or naked flames, the membrane creates completely watertight seams prior to the installation of steel reinforcement and poured concrete. No protective layer is required, other than a temporary peel-off protection film which is removed before steel fixing. Once the concrete is poured, the system is fully bonded and prevents water from migrating laterally between the foundation structure and the membrane.
The post-applied self-adhering version, Mapeproof AL 1200 AP, was then lapped onto the pre-applied membrane and continued upwards for the cast tunnel and ventilation shaft walls. Mapei’s Polyfond Kit Drain – a robust, cuspated HDPE membrane laminated with a polypropylene needle-punched nonwoven geotextile – was also used to protect the membrane against backfilling works.
Tunnel joints were further protected against potential water ingress with the Idrostop Multi re-injectable hose system and Idrostop preformed hydrophilic acrylic polymer profile strips.
Mapeproof AL AP System provides a robust membrane is highly resistant to both puncturing and tearing. It can be applied underneath foundations, on formworks (precast), against diaphragms, soldier pile walls, pile walls or other excavation structures. Find out more about it, and all of our products, here.
