Engineers examine a piled secant wall adjacent to existing railway forming a ventilation shaft on Channel Tunnel Rail Link
A secant wall is a special kind of piled foundation where two adjacent piles have another bored between them. The piles form a water resistant interlocking structure which is important in areas with a high water table or unstable ground. They are formed by auger piling and, due to low noise and vibration, secant walls structures are often constructed near to roads, railways and sensitive buildings - as here, where the ventilation shaft is adjacent to a domestic rail line. The £ billion Channel Tunnel Rail Link (now High Speed One) was built between 1998-2007 and partly funded by the European Union, it forms a section of the Trans European Rail Network. It is basically a French-style high-speed rail line linking London with the Channel Tunnel, the Eurostar trains were developed on proven technology from the French TGV high-speed system. Stations on the CTRL are the existing Ashford International and new stations at Ebbsfleet and Stratford. The line ends at the rebuilt St. Pancras. Fourteen new tunnels were constructed, the longest being the London Tunnel which is long from Ripple Lane to Stratford, after which the line briefly comes to the surface at Stratford Station. Five huge shafts of diameter ventilate the twin bore, single-track tunnels and provide emergency access and evacuation points. The line passes in tunnel under the River Thames and crosses the M25 at Thurrock. For the Thames crossing (a 3km twin-bore tunnel), the line drops 1 in 40 down under the river and then climbs 1 in 40 up, curving at the same time. The CTRL then negotiates the M25 motorway, going under the southbound and over the northbound carriageway. Lengthy loops at two places along the route allow trains to be overtaken so freight and faster domestic trains can be mixed with 300 kph Eurostar high-speed services.
Size: 3310px × 3310px
Location: Dagenham, London, UK.
Photo credit: © qaphotos.com / Alamy / Afripics
License: Licensed
Model Released: No
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