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New 9km tunnel for UK high speed rail 23 Apr 2013
Peter Kenyon, TunnelTalk
A study commissioned by HS2 is recommending an additional 9km of 8.7m diameter twin-running TBM-bored tunnel be added to the Phase 1 alignment between London and Birmingham.
The revised alignment, which will run on to the existing Ruislip tunnel to create a single 14km-long tunnel, is almost certain to be implemented by the UK Department of Transport. The new recommendation follows an engineering study that was commissioned to investigate objections spearheaded by the local council in the London Borough of Ealing.
The alignment change results in an almost continuous 22km-long tunnel under north and northwest London. Starting from just west of the terminus at the new Euston Station the amended alignment runs 8km through to the Old Oak Common station box and then, continuing eastwards, for a further 14km to the Ickenham Portal at West Ruislip.
New tunnel runs from Old Oak Common Station box, eastwards...

New tunnel runs from Old Oak Common Station box, eastwards...

...where it joins existing 5km tunnel, removing the need for tunnel portals at Northolt and North Acton

...where it joins existing 5km tunnel, removing the need for tunnel portals at Northolt and North Acton

The decision cuts out the 9km-long overground part of the route between Old Oak Common Station and Northolt. Objectors led by the local council in Ealing pointed out that the existing plan would have required replacement or demolition of 20 bridges and a complete redesign of the busy Hanger Lane traffic intersection, one of the main choking points for commuter traffic from the west into central London.
HS2 spokesman Adam Joyce told TunnelTalk: "We are recommending to the Department of Transport the addition of 9km of TBM-bored tunnel to create a 14km-long single continuous tunnel between Old Oak Common and West Ruislip. Our recommendation will now be subject to a new consultation period, but we expect the latest proposal will be acceptable because the consensus of local opinion is likely to be strongly in favour of the change." He added: "A more precise study of the cost of relocating and replacing bridges and utilities along the surface route revealed that they were similar to simply allowing the TBMs to continue from west of Old Oak Common Station through to Northolt and on to the planned portal at West Ruislip." According to the study the tunnel option will take 15 months less to construct, and will require an additional three vertical shafts though this will be compensated for by there now being no need for a tunnel portal at Northolt.
Complex Hanger Lane traffic gyratory system

Complex Hanger Lane traffic gyratory system

The recommendation announced today (23 April 2013) follows the addition last year of a further 5km of twin running tunnel alignment under the neighbouring London Borough of Ruislip, and the linking of two separate tunnels of 1.25km and 9.5km in rural Buckinghamshire to create a continuous 13.5km-long tunnel. Since the UK Government launched its consultation process for High Speed Rail 2 in 2010, an additional 16.5km of twin-running TBM bored tunnel and a further 8km of so-called 'green' cut-and-cover tunnels have been added.
Initial scope for approximately 20km of TBM bored twin-running tunnels in four separate sections along the 224km route between London and Birmingham is now increased to 37km, plus an additional 8km of 'green' tunnels for a total underground alignment of 46.2km, or nearly 20%. Phase 2, between Birmingham and Manchester and Birmingham and Leeds, calls for a further 20.77km of TBM-bored twin running tunnels plus 1,560m of cut-and-cover tunnel.
The HS2 spokesman said the decision to extend tunnelling as far west as Ickenham did not affect possible future plans for a high speed rail spur to Heathrow Airport, details of which have been delayed until after the Davies Commission on future airport capacity reports back to Parliament in Summer 2015. This additional planned route is expected to include a large element of tunnelling.
Joyce said: "There will be an interchange at Old Oak Common for onward (non-high speed service) access to Heathrow. Any future (high speed) spur would start on a surface section from Ickenham out of London."
Table 1. Underground alignments proposed for HS2 London-Birmingham
Location Distance from Euston Station Tunnel Length Tunnel type
Euston Station - Old Oak Common Station box 500m - 8,500m 8,000m TBM
Old Oak Common Station box 8,500m - 9,500m 1,000m Station box
Portal west of Old Oak Common Station box - Ickenham Portal (West Ruislip)** 9,500m - 23,500m 14,000m TBM
Chalfont St Peter - Little Missenden* 31,500m - 45,000m 13,500m TBM
South Heath 46,500m - 47,600m 1,100m Green
Wendover 53,500m - 54,600m 1,300m Green
Turweston 95,000m - 95,100m 100m Green
Greatworth 102,000m - 104,100m 2,100m Green tunnel
Chipping Warden 110,000m - 112,500m 2,500m Green
Ulton Woods 127,000m - 127,400m 400m Green
Ulton Woods 127,400m - 128,900m 1,500m TBM
Burton Green 146,000m - 146,520m 520m Green
TOTAL n/a 46,020m 11+Stn. box

*   2,400m tunnel section added January 2012
** 5,000m section (Northolt-Ickenham added January 2012), 9,000m section
    (Old Oak Common Station box-Northolt added April 2013)

References
UK High Speed 2 needs 56km of twin tunnels - TunnelTalk, January 2013
Extra tunnels seal UK high speed rail approval - TunnelTalk, January 2012

           

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