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TBM on schedule for Crossrail tunnels

Herrenknecht delivers for Crossrail, Alcontrol advances analysis, Sandvik improves reliability and Bauer adds to slurry technology.

Crossrail’s tunnels will start to become a reality this year with four tunnel boring machines (TBMs) set to start work on the underground parts of the long-awaited new rail network. Parts for the first Crossrail TBM have now arrived on site near Paddington from Herrenknecht’s German factory for assembly ahead of its scheduled March launch date.

The first 1,100t earth pressure balance (EPB) machine will be used to drive the 6.16km from Royal Oak eastwards to Farringdon and will be followed shortly after by a second machine boring the parallel twin tunnel. In total six EPB and two mixshield machines - all from Herrenknecht - will be used for the 21km of twin-bore tunnels on the new 118km rail link from Maidenhead to Shenfield in Essex and Abbey Wood in Kent.

The 140m long TBM will use the 7.1m diameter cutter head and 7.08m shield to drive the tunnel, which will be lined with precast concrete segments, grouted into position, to form the 6.2m internal diameter tunnel.

Power for the machine’s 1.9MW main drive will come from 11kVA connections into the national grid along the route. They will rotate the cutter head at up to 3.19rpm to achieve the 100m per week target. Crossrail’s EPB machines will operate at pressures of up to 300kPa and will mainly be tunnelling through London Clay, although the eastern end will move into the sands and clays of the Lambeth Group and Thanet Sand before the mixshield TBMs take over to drive the north Kent tunnels through chalk.

According to Herrenknecht division manager for traffic tunnels, Gerhard Wehrmeyer, Crossrail set a very clear specification for the TBM design: “All the EPB machines are very similar, although there are a few minor differences between what each contractor has ordered. Crossrail agreed a common specification to ease the parts and maintenance issues.”

This common procurement route has helped to cut the delivery time for the machines from the normal 12 months to 10. “Each machine has 2,000 drawings and 500 assembly drawings so being able to duplicate these between the machines has helped reduce the design work needed,” adds Wehrmeyer. One area where Crossrail’s specification went beyond what is normally expected was in terms of the belt scales fitted to the conveyors.

“Only one manufacturer - Australia’s CST - could match the high specification,” says Wehrmeyer. Crossrail chief engineer Chris Dulake explains that this demand was placed on Herrenknecht to help avoid collapses such as those in Lavender Street in east London, when TBMs for the High Speed 1 line to the Channel Tunnel passed through previously unrecorded well shafts.

“The high accuracy of the belt scales will help ensure that the material being extracted at the face as the TBM advances exactly matches the expected volume,” he says. “If there is any difference between the two, then we know there is a problem.”

Material from the face will be transported over the belt scales and back through the tunnel via a conveyor system built by Herrenknecht subsidiary H+E Logistik.

The TBM is controlled from an operator’s cab just behind the tunnel shield. Displays show the earth and advance pressure, material transport and shield articulation, as well as viewing work from five CCTV cameras located around the machine. Guidance information from the VMP laser system is also displayed.

Work to produce the 70,000 precast concrete segments for the scheme is also gearing up in two factories - at Old Oak Common for the western tunnel and Chatham, Kent for the eastern tunnels. The factories are producing two types of segment to enable them to line left and right-hand bends. A mix of the two will be used for straight sections of the route.

The first TBM is set to start work in March and is expected to reach Farringdon in summer 2013. The second EPB machine will also soon arrive at Royal Oak for assembly while work on the remaining four EPB machines and two mixshield TBMs continues in Germany.

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