Northolt tunnel
 HS2 route running west from London Euston, through Old Oak Common towards Ruislip | |
| Overview | |
|---|---|
| Coordinates | 51°32′10″N 0°19′08″W / 51.536°N 0.319°W |
| Status | Under construction |
| System | High Speed 2 |
| Crosses | West London |
| Start | Old Oak Common railway station |
| End | Ruislip |
| Operation | |
| Traffic | Rail |
| Technical | |
| Length | 8.4 miles (13.5 km) |
| No. of tracks | 2 |
| Track gauge | 1,435 mm (4 ft 8+1⁄2 in) |
| Electrified | 25 kV 50 Hz AC |
| Operating speed | 320 km/h (200 mph) |
| Width | West - 8.8 metres (29 ft) East - 8.1 metres (27 ft) |
The Northolt Tunnel is a high-speed railway tunnel currently under construction in Greater London, England, and will upon completion carry the High Speed 2 (HS2) railway line under the West London suburbs. The twin-bore tunnels will run for 8.4 miles (13.5 km) between Old Oak Common 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 102 km (63 miles) of tunnels 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 will be 5 miles (8.0 km) long 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 will 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 will then become the Green Park Way ventilation shaft.[9][10]
In advance of the tunnel's boring, a smaller logistics tunnel will be bored using a separate TBM that will 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 will be brought into the site and spoil 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, named Caroline (after astronomer Caroline Herschel) and Sushila (after a local teacher), arrived at the West Ruislip launch site to dig the western section of the tunnel in December 2021;[11] with TBM Sushila launching on 6 October 2022 [12] and Caroline following suit on 27 October.[13] Completion is currently scheduled for August 2024.[14][15]
Progress
As of 23 November 2022[update], TBM Sushila, the first machine to be launched from the West Ruislip portal, had progressed a distance of 0.218 km (0.14 miles) from the north portal, with a remaining distance of 7.622 km (4.74 miles), [16] while TBM Caroline, the second machine to be launched, had completed 0.027 km (0.02 miles), with 7.813 km (4.85 miles) remaining.[16]
References
- ^ Horgan, Rob (14 June 2021). "The reality of working on HS2's biggest construction site". newcivilengineer.com.
- ^ "The Government response to the design refinement consultation: Decisions and Safeguarding Directions for Northolt and Bromford" (PDF). gov.uk. October 2013.
- ^ "HS2 tunnel confirmed for Ealing and Northolt". BBC News. 24 October 2013. Retrieved 3 July 2021.
- ^ Watts, Joe; Beard, Matthew (25 April 2013). "HS2 tunnel extended under west London to cut chaos". Evening Standard. Retrieved 3 July 2021.
{{cite web}}: CS1 maint: url-status (link) - ^ Croxford, Rianna (16 March 2018). "HS2 builders find ancient sub-tropical coastline in west London". Financial Times.
- ^ "Workers discover ancient coastline in West London". HeritageDaily. 16 March 2018. Retrieved 3 July 2021.
{{cite web}}: CS1 maint: url-status (link) - ^ "Proposal for Northern Extension of Northolt Tunnel SIFT Report" (PDF). High Speed 2. 27 February 2015. Retrieved 3 July 2020.
{{cite web}}: CS1 maint: url-status (link) - ^ "HS2's contracts awarded – includes £3.3 billion London tunnels". IanVisits. 15 April 2020. Retrieved 3 July 2021.
{{cite web}}: CS1 maint: url-status (link) - ^ a b c d "Order goes in for Northolt tunnels TBMs". The Construction Index. 12 October 2020. Retrieved 3 July 2021.
- ^ a b Long Branch, Mike (22 February 2021). "HS2 Prepares for 21km tunnels under London (Tunneltalk)". londonreconnections.com.
- ^ Menteth, Thames (20 December 2021). "HS2: First London TBMs arrive at site for 2022 launch". Ground Engineering (GE). Retrieved 23 December 2021.
- ^ Mansfield, Ian (6 October 2022). "HS2 starts digging 26 miles of tunnel under London". IanVisits. Retrieved 6 October 2022.
- ^ "HS2 construction in London gathers pace as second tunnelling machine sets off underneath the capital". High Speed 2. 27 October 2022. Retrieved 13 November 2022.
- ^ Hakimian, Rob (15 July 2022). "HS2 timeline of major events to 2025 revealed". New Civil Engineer. Retrieved 16 July 2022.
- ^ "'HS2 drill switch-on is milestone for the ambitious project'". BBC News. 6 October 2022. Retrieved 6 October 2022.
- ^ a b "HS2: In your area map". HS2 Ltd. Retrieved 13 November 2022.