The project’s first two sprayed concrete tunnels have been constructed under Finsbury Circus in the City of London. The works are part of construction for Crossrail Liverpool Street station. The 4.5 metre diameter tunnels have been built from the main access shaft within the Finsbury Circus worksite.
The two tunnels are temporary structures and will be used for compensation grouting, one of the ways that Crossrail will control any ground movements that could result from tunnelling activity.
Small diameter tubes (Tubes a’ Manchette) will be drilled and installed from the temporary tunnels allowing the contractor to inject grout into the ground. This will stabilise the ground and limit surface settlement.
A Sprayed Concrete Lining (SCL) technique has been used to build these tunnels. This technique involves rapidly spraying the excavated ground with concrete to stabilise it and form the permanent tunnel lining. The first SCL tunnel measures 80 metres in length and the second (running east from the worksite) is 100 metres long.
The Spray Concrete Lining technique will be used to build 12 km of station platform tunnels, passages, access and grout tunnels along the Crossrail route where smaller, relatively short tunnels are needed.
Unlike bored tunnels which are built using a tunnel boring machine, SCL allows variation in the tunnel shape and diameter and 7.5 km of SCL tunnels will become permanent features of the project.
Colin Niccolls, Crossrail’s Whitechapel & Liverpool Street Platform Tunnels Project Manager said: “Crossrail will primarily use two different types of tunnelling technique to build the new rail tunnels and stations. While tunnel boring machines will create the new rail tunnels, work has commenced on creating the station tunnels using mining techniques to excavate the ground which is then sprayed with shotcrete to form the tunnel linings.”
Once Crossrail works are completed at Moorgate in 2017, Finsbury Circus will be re-instated to its pre-construction condition.
Gallery - Crossrail’s first spray concrete lined tunnels completed under Finsbury Circus
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Notes to Editors
The works are being undertaken by BBMV JV (Balfour Beatty Civil Engineering, Alpine BeMo Tunnelling, Morgan Sindall and VINCI Construction) as part of the C510 contract – Early Access Shafts and Spray Concrete Lining works for Whitechapel and Liverpool Street station tunnels.
The total funding envelope available to deliver Crossrail is £14.8bn.
The Crossrail route will pass through 37 stations and run 118 km (73 miles) from Maidenhead and Heathrow in the west, through new twin-bore 21 km (13 miles) tunnels below central London to Shenfield and Abbey Wood in the east.
When Crossrail opens it will increase London's rail-based transport network capacity by 10%, supporting regeneration and cutting journey times across the city. Crossrail services are due to commence through central London in 2018.
Crossrail is being delivered by Crossrail Limited (CRL). CRL is a wholly owned subsidiary of Transport for London. Crossrail is jointly sponsored by the Department for Transport and Transport for London.