Copthall tunnel and Sustainable Placement Area
The design for the Copthall Tunnel and the Northern Sustainable Placement Area (NSPA) has been developed with consideration for the technical and structural requirements as well as the impact on their surroundings. This has involved reviews with Hillingdon Council.
The Copthall Tunnel will be located within the London Borough of Hillingdon, between Harvil Road in the west and Breakspear Road South in the east. The site is north of the existing Chiltern Line railway and south of Newyears Green Lane.
The proposed Copthall Tunnel will include two portal entrances at either end, a single-track siding, and five natural ventilation openings at 200 metre intervals along the top of the tunnel. The tunnel will be constructed using a cut and cover technique, with material being excavated to facilitate the construction of the tunnel concrete box structure. This will then be covered using excavated material, and a new a landscape constructed on top.
The designs for the Copthall Tunnel differ from the designs that were included within the HS2 Environmental Statement, which showed a cutting (Copthall Cutting) as opposed to a tunnel. Following a review of the Copthall Cutting design the decision was made to change the design to a cut and cover tunnel instead. This new design provides two main benefits:
- The reuse of material on site (approximately 1.1 million cubic metres) resulting in a substantial reduction in the number of lorries required to take the material away from site whilst using the local highway network.
- The cut and cover tunnel ensures a better, greener integration of the railway within the surrounding landscape, reducing its visual impact.
Northern Sustainable Placement Area
The proposed Northern Sustainable Placement Area will be located to the north of Newyears Green Lane, west of Breakspear Road South and south of Bayhurst Woods. Within the NSPA, mounds will be formed using excavated material arising from nearby HS2 work sites, specifically the excavations required for the construction of the Copthall Tunnel.
There will be two separate sites where the mounds will be located:
- Western mounds – Situated on land immediately to the north of Newyears Green Lane. The mounds will rise to 18 metres in height above existing ground level at its highest point. The mound will consist of approximately 209,000 cubic metres of material.
- Eastern mounds – Situated on land immediately to the north of Newyears Green Lane and west of Breakspear Road. The mounds will rise to 18 metres in height above existing ground level at its highest point. The mound will consist of approximately 468,000 cubic metres of material.
The excavated material that will be used to form the mounds, will be transported to the NSPA sites internally within the HS2 work compounds. Internal movements of the material will negate the need to use the local highway network. An overhead conveyor will also be constructed across Newyears Green Lane and will connect the HS2 sites that are to the north and south of Newyears Green Lane.