HS2 Chiltern tunnel hits halfway mark

Progress on Colne Valley viaduct continues

On Phase 1 of HS2, boring of the 10-mile-long Chiltern tunnels has reached the halfway stage, with Tunnel Boring Machines Florence and Cecilia passing the halfway mark on their drives.

Excavation of the five ventilation shafts on the tunnels has now been completed: these are sited at Chalfont St Peter, Chalfont St Giles, Amersham, Little Missenden and Chesham Road. In excess of 56,000 fibre reinforced tunnel lining segments have been installed, with each made on site in a temporary factory.

So far, more than 1.3 million cubic metres of chalk and flint have been excavated. This will be used to help create 127 hectares of new landscaping, wildlife habitat and chalk grassland.

Halfway there: HS2's Chiltern tunnel
Halfway there: HS2's Chiltern tunnel HS2 Ltd

The final piles on the 2.1-mile-long Colne Valley viaduct have now been installed to support 56 piers on the structure, which will be one of the longest railway bridges in Britain. To support piles in lakes, temporary jetties with cofferdams were installed. These jetties are used to transport materials and equipment during construction of the piers and viaduct deck. When the piles are completed, a concrete pile cap is installed to support the structure. The piles were bored into the ground before being backfilled with concrete.

On Phase 2b from Crewe to Manchester, alterations have been made around the proposed station at Manchester Airport, which would also serve Northern Powerhouse Rail. Under revised proposals, the M56 motorway would be realigned to the south with Junction 6 converted to a roundabout junction with HS2 running in a shallow tunnel underneath. A direct road link would be provided to the station with a flyover crossing Hale Road and running parallel to the M56. Community engagement sessions are to take place in the area in early March on the proposed changes.