Trains will emerge from the Chiltern Tunnel into South Heath cutting which will be 16 metres deep. The portal is on farmland just north of Frith Hill. The construction compound will be approximately 1.5ha in size and be in place for eight years. Access to the compound will be via a newly constructed temporary haul road from the Link Road roundabout on the A413 at great Missenden. Realignment of one PRoW (Public Right of Way) will be required. Footpath GMI 13 will be closed during construction and then be permanently diverted to the south of the tunnel portal.
The former Weights & Measures Gym (previously the Black Horse public house) was demolished to allow permanent access to the portal from Frith Hill. A series of 96 piles (barrettes) were installed to the north of Frith Hill to support the last 200 metres of the tunnel through soft clay. There will be an ancillary building and an area of hard standing alongside the track within the South Heath cutting.
The tunnel boring machines reached here in February and March 2024. They were then be dismantled and removed.
North of the tunnel portal The contractors change from Align JV who are building the Colne Valley viaduct and the Chiltern tunnel to EKFB who will construct the railway across Buckinghamshire.
In July 2024 the contract to construct the line from the north portal to Leather Lane was passed from EKFB to Align.
Please note the tunnel portal is the tunnel’s entrance. The tunnels will have porous portals made from concrete and designed to allow the passage of air from the tunnel to reduce both air pressure changes and the noise generated when trains enter and leave the tunnel.