HS2 | BTS
Tunnel configuration at Old Oak Common Station
in November 2023. This tunnel connects the SCS logistics hub with the very eastern end of the OOC station box and will be instrumental in the delivery of the Euston Tunnels. There are further SCL tunnels, 370m-long, at the
west end of the station box. These connect to a cross over box outside the station and are up to 13m in diameter to allow for diverging tracks. These tunnels were driven with a full-face pilot tunnel circa 5m-diameter then enlarged to full face. Typical lining thickness are 300mm-400mm for the primary lining and 275mm to 400mm for the secondary. At the time of the BTS presentation, the primary lining here was 75% complete and on hold awaiting a utility diversion. West of the crossover box are some further short SCL tunnels and a shaft making up the launch arrangements for the Northolt Tunnel East.
Northolt Tunnel East (NTE) The NTE tunnels are 5.6km-long, 8.1m ID and were driven by an EPBM machine in semi open mode for a majority of the drive. They passed through one ventilation shaft at Westgate and terminated at a reception shaft at Greenpark Way. There are 14 CPs up to 30m in length, comprising
of a primary lining, circa 250mm-thick, a sheet waterproofing membrane and a cast insitu secondary lining of 250mm thickness. With the exception of the last CP no ground treatment was required. Greenpark Way shaft is the reception shaft for both
the NTE tunnels – driven west, and also the NTW tunnels driven east. The TBMs were received, in turn, into a reception can and then removed from the shaft. All have been successfully received.
Northolt Tunnel West (NTW) The NTW tunnels were launched from a portal structure 250m-long at West Ruislip. A shallow launch methodology was used with additional temporary kentledge incorporated at the portal. The tunnel is 8.8m in diameter and was driven by an EPBM in closed mode for 7.8km to Greenpark Way shaft, via intermediate shafts at South Ruislip and Manderville Road. There are 20 CPs of similar construction to the NTE ones. Due to the ground conditions a mixture of dewatering and ground freezing was employed.
Copthall Tunnel The final section of tunnelling for SCS is the Copthall Tunnel, a cut-and-cover tunnel approximately 1km in length, west of the Northolt tunnel portal. This is a twin-track, bi-directional, cast insitu cut-and-cover tunnel with a maximum overburden of about 16m. Originally this was to be a cutting, but the tunnel
was introduced partly to assist with the re-use of the spoil from NTW.
It is the only twin-track bi-
directional tunnel on the project and consequently has several permanently open air-shafts for ventilation and aerodynamic considerations.
The Chiltern Tunnels The Chiltern Tunnels are the longest rail tunnels in the UK at 16km in length, and 9.1m ID. These were driven by Variable Density slurry TBMs, at a depth of up to 90m, though chalk with the added pressure of crossing under the M25 within 300m of the launch. The tunnel passes through five shafts up to 63m deep at Chalfont St Peter, Chalfont St Giles,
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