Canal Tunnels

The Canal Tunnels were constructed as part of the wider Thameslink Programme; a £6 billion project to upgrade and expand the Thameslink rail service crossing the capital. These tunnels were the first major element of Thameslink's infrastructure to commence construction.[3][4] One primary purpose of the tunnels was to facilitate the integration of services running on the East Coast Main Line (ECML) into the Thameslink network; a junction connecting the tunnels to the ECML is positioned barely 100 metres from the northern portals.[3][4]

The tunnels were designed by Halcrow Group, part of the Rail Link Engineering consortium, with safety and resilience in mind. The construction process itself took roughly two years, with civil works commencing in 2004 and completed in 2006. Design and construction of the tunnels were planned to integrate with the adjacent railway engineering works for the Channel Tunnel Rail Link High Speed 1 and redevelopment of the Railway Lands and St Pancras railway station.[4][2] The tunnels were driven using tunnel boring machines (TBMs). Each bore is 6 metres (20 ft) in diameter and lined with pre-cast concrete segmental rings. The northbound tunnel is 860 m (2,820 ft) in length, while the southbound tunnel is 820 m (2,690 ft) long; this length discrepancy is due to curvature.[3] The tunnels feature relatively steep inclines, at some point as high as 1 in 34; the lowest point of these gradients was deliberately positioned in line with the incorporated flood control measures.[2][5]

While power is normally directed from infrastructure built for the nearby Midland Main Line, provisions to use the ECML's power supply have been made.[3] For safety reasons, emergency service radio systems have been installed, along with a walkway and automated LED lighting at four-metre intervals to provide an escape route in the event of a passenger evacuation within the tunnel. On account of the Regent Canal's close proximity, flood management measures were also built, including a drainage system with a sizable sump beneath the tunnel, which is pumped into the ECML's existing drainage network.[3][2] The infrastructure has been designed to facilitate bi-directional working for greater operational flexibility.[4][3]

Despite their problem-free completion, the Canal Tunnels remained unused for several years. This was largely due to the tunnels having been completed well in advance of numerous other Thameslink elements, such as delivery of the new British Rail Class 700 multiple units ordered for the service and other infrastructure works.[4][2] During this interval, the installation of track, power supply, and signalling systems were performed ahead of the commencement of passenger services. In August 2012, railway infrastructure owner Network Rail announced that the construction company Carillion had been appointed as the principal contractor for the fitting-out of the Canal Tunnels.[2]

The fitting-out process commenced during 2013 and was completed during the following year, despite this milestone occurring several years ahead of services running; this was reportedly to facilitate stock movements and to take advantage of available land to facilitate such work.[4] The signalling systems installed were integrated with Thameslink's High Capacity Infrastructure; in addition to conventional colour light signalling, the European Train Control System is present; Thameslink officials claimed that this arrangement was the world's first implementation of such technology on a mainline 'heavy' railway.[3] Wherever possible, all wiring, mechanical, and electrical equipment was cleanly run within a pair of troughs built into the tunnel. Amongst the last elements of the work was the connection of the new track to the existing lines via the insertion of several new junctions.[2][6]

King's Cross & St Pancras approaches
Midland ML & Thameslink to Kentish Town ECML & Thameslink to Finsbury Park Copenhagen Junction North London line to Gospel Oak North London line to Highbury & Islington High Speed 1 to Stratford International Regent's Canal Canal Tunnels Gasworks Tunnel St Pancras King's Cross Thameslink to Blackfriars

On 26 February 2018, the first passenger service traversed the Canal Tunnels; numerous out-of-service trains traversed the section prior to this for testing purposes.[3][7] The tunnels were officially opened to traffic during May 2018, forming a part of the Thameslink core route from that month onwards.[4] Until then, capacity had been limited to 16 trains per hour from Bedford, Luton and St Albans southbound via the Midland Main Line; the presence of the Canal Tunnels added another 8 per hour from Cambridge and Peterborough, achieving the objective of a peak service of 24 trains per hour between St Pancras and Blackfriars.[3][8] Many of these movements are automated, making use of the route's sophisticated digital signalling.[3]

• Case Study on the Canal Tunnels via swordgroup.co.uk
• Thameslink 2000 tunnels via researchgate.net