Northolt tunnel

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Northolt tunnel
Overview
StatusUnder construction
SystemHigh Speed 2
CrossesWest London
StartOld Oak Common railway station
EndRuislip
Operation
TrafficRail
Technical
Length8.4 miles (13.5 km)
No. of tracks2
Track gauge1,435 mm (4 ft 8+1⁄2 in)
Electrified25 kV 50 Hz AC
Width9.1 metres (30 ft)

The Northolt tunnel will carry the High Speed 2 (HS2) railway line under West London, England. The twin-bore tunnels will run between Old Oak Common railway station and Ruislip.

Plans for the construction of a tunnel were first unveiled in early 2013; it was hailed as being less disruptive and quicker to construct that a surface-based alignment. An option for the tunnel's extension along the Colne Valley to replace the proposed Colne Valley Viaduct was studied but rejected as unnecessarily costly during 2015. Extensive ground surveys along the intended route were conducted during the 2010s in advance of construction work. During April 2020, it was announced that a contract worth approximately £3.3 billion had been awarded to a joint venture company, Skanska Costain Strabag, for the tunnel's construction.

History[]

The construction of the High Speed 2 (HS2) railway is to involve numerous major civil engineering works along its intended route; it has been anticipated that around the 102 km (63 miles) of tunnels that are to be bored along various parts of its route in order to accommodate it.[1] During early 2013, it was confirmed that this section of HS2 would be constructed in a tunnel, rather than above ground.[2] At the time, HS2 Ltd, the delivery company behind the line, stated that the use of a tunnel was the optimum solution, reducing the disruption caused by the railway's construction upon the local community while also accelerating the timetable for that portion of the route.[3][4]

Prior to any construction activity commencing, numerous surveys and ground investigations were conducted along the intended route; the effort was described by Steve Reynolds, HS2’s ground investigation programme manager, as "the largest ground investigation programme that the UK has ever seen".[5] During early 2018, a layer of black clay was discovered, which has been dubbed the "Ruislip Bed"; this material dates back 56 million years and was formed from densely wooded marshes at the coast of a sub-tropical sea.[6]

During the early-to-mid 2010s, the possibility of extending the tunnel to traverse the Colne Valley, as an alternative to the proposed Colne Valley Viaduct, was examined in detail. However, this option was formally dismissed in a report released in February 2015, primarily due to the increased costs and construction time that such a change would predicted to involve.[7]

During April 2020, it was announced that a contract had been awarded to a joint venture company, Skanska Costain Strabag, for the tunnel's construction.[8] In October 2020, it was revealed that Herrenknecht would be supplying the two tunnel boring machines (TBMs) that will be used in the boring of the western section.[9]

Construction[]

It is planned for the tunnel to be bored in two sections; the western section shall have a length of 5 miles (8.0 km) and the eastern section will be 3.4 miles (5.5 km)[9] Of these, 13.7 km (8.5 miles) has been designed as a twin bored tunnel, which shall be excavated using a total of four TBMs. Following the completion of boring, all four TBMs are to be retrieved at the point where the two sections meet; this site shall subsequently become the Green Park Way ventilation shaft.[9][10]

In advance of the tunnel's boring, a smaller logistics tunnel is to be bored using a separate TBM that'll facilitate access between the primary construction compound at Atlas Road and Old Oak Common Station, the launch site for the Northolt East and Euston TBMs, through which construction materials such as the precast concrete lining segments shall be brought into the site and spoil shall be removed.[10] Delivery of the first TBMs has been scheduled to occur some time prior to the end of 2021, while boring work is set to commence during mid-2022.[9]

The first two TBMs arrived at the West Ruslip launch site to dig the western section of the tunnel in December 2020.[11]

References[]

  1. ^ Horgan, Rob (14 June 2021). "The reality of working on HS2's biggest construction site". newcivilengineer.com.
  2. ^ "The Government response to the design refinement consultation: Decisions and Safeguarding Directions for Northolt and Bromford" (PDF). gov.uk. October 2013.
  3. ^ "HS2 tunnel confirmed for Ealing and Northolt". BBC News. 24 October 2013. Retrieved 3 July 2021.
  4. ^ Watts, Joe; Beard, Matthew (25 April 2013). "HS2 tunnel extended under west London to cut chaos". Evening Standard. Retrieved 3 July 2021.
  5. ^ Croxford, Rianna (16 March 2018). "HS2 builders find ancient sub-tropical coastline in west London". Financial Times.
  6. ^ "Workers discover ancient coastline in West London". HeritageDaily. 16 March 2018. Retrieved 3 July 2021.
  7. ^ "Proposal for Northern Extension of Northolt Tunnel SIFT Report" (PDF). High Speed 2. 27 February 2015. Retrieved 3 July 2020.
  8. ^ "HS2's contracts awarded – includes £3.3 billion London tunnels". IanVisits. 15 April 2020. Retrieved 3 July 2021.
  9. ^ a b c d "Order goes in for Northolt tunnels TBMs". The Construction Index. 12 October 2020. Retrieved 3 July 2021.
  10. ^ a b Long Branch, Mike (22 February 2021). "HS2 Prepares for 21km tunnels under London (Tunneltalk)". londonreconnections.com.
  11. ^ Menteth, Thames (20 December 2021). "HS2: First London TBMs arrive at site for 2022 launch". Ground Engineering (GE). Retrieved 23 December 2021.


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