Page 12 - Contractors World -UK & Ireland Vol 2 No 4 (May 2012)

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First spray concrete lined tunnels completed
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 m in length and the second (running east from the worksite) is 100 m 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, 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.”
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.
Works at Connaught Tunnel pick
up pace
Cros s ra i l ha s begun dr i l l i ng we l l s at
Connaught Tunnel to draw down the water
table ahead of works to deepen and widen
the 130 year old tunnel in east London.
Once the wells are completed, drawing
down of the water table wi l l begin next
Page 12
Contractors World - UK & Ireland Vol 2 No 4