Tunnel vision: London’s Crossrail enters its final leg

Under 2km of tunnels remain of the 42km needed for the £14.8bn infrastructure project, due to be finished in 2017

 Crossrail breakthrough into the east-end of Crossrail's Liverpool Street station in London.

Crossrail breakthrough into the east-end of Crossrail’s Liverpool Street station in London.

Elizabeth, one of the last tag team of Crossrail tunnelling machines, has made the first breakthrough into the City of London, 40 metres below ground under Liverpool Street. The moment when the 6.2 metre-wide drill head cut through the wall into the hollowed-out future station marked the start of the final phase of excavation for the £14.8bn project, with just under 2km remaining of the 42km of tunnels to be dug under the capital. The final link-up of all the tunnels will be achieved in the spring, fittingly, by sister machine Victoria at Farringdon: the destination of the world’s very first underground train in the last queen’s reign, 152 years ago.

Tunnelling technology has moved on somewhat since then, but the crew of 20 on each tunnel-boring machine still have an uncomfortable, difficult task, working 12-hour shifts around the clock. Their workplace is essentially a mobile, underground factory, located claustrophobically at what was, until the breakthrough, a 7km-long dead end. Behind the slowly turning cutter head is a 148-metre-long train of hydraulic rams, control rooms, conveyors, piping and steel walkways, creating a tunnel and laying tracks while spewing out the Londonclay behind. Seated at a computer console near the front, a controller monitors an array of panels to guide the machine forward, a 1,000-tonne monster that must not deviate inches from its precise path through a subterranean warren.

Its journey, of around 100 metres a week on average, takes place in 1.6 metre steps: the width of the concrete tunnel segments that are funnelled to the front when the drill has eaten out enough space. In the noisiest, dirtiest and trickiest part of the job, the teams ensure that the 3.5 tonne blocks are swung cleanly into place by Elizabeth’s hydraulic arms, to be grouted and bolted to create a new ring of tunnel, from which the machine can push on again.

A tunnelling breakthrough is always a moment of celebration for the crew, as well as one of relief for Crossrail’s engineers and architects. But for the machines, they can often mean the end: like male bees, climaxing and perishing. Elizabeth will have one last push to Farringdon, 750m further west, where her steel shell will be subsumed into the tunnel lining, although much of her innards will be stripped out and live to drill another day. Some of the other seven boring machines have reached their final resting place underground. Phyllis, having made it to the same destination from Paddington in the west, was steered irreversibly into the earth, her shell and cutter head encased in concrete and buried with a time capsule in Charterhouse Square for future archaeologists to uncover.

The chief executive of Crossrail, Andrew Wolstenholme, said: “We are now on the final countdown to the big east-west breakthrough at Farringdon, which will link all of Crossrail’s tunnels for the first time. This is a phenomenal feat of civil engineering that London can be justifiably proud of. The next challenge is to implement railway systems across the route, keeping the project on time and within budget.”

After tunnelling is complete, around three more years of work will remain before Crossrail’s trains run under the heart of London. These great empty spaces, running from Paddington to Canary Wharf and beyond, will be fitted out for 200 metre-long trains carrying 1,500 passengers every five minutes. The first new Crossrail trains will start arriving in Liverpool Street on existing overground tracks in the east from 2017. When the new railway does, properly, cross the capital in 2019, it will boost capacity by 10% and bring an extra 1.5 million people within a 45-minute commute of central London.

An academy set up as part of Crossrail is expected to feed a new generation of skill British tunnelling workers into projects such as HS2 – and, in London’s next big ambitious project being increasingly championed by transport planners, Crossrail 2.


Source: http://www.theguardian.com/uk-news/2015/jan/29/crossrail-london-enters-final-stage-drilling-breakthrough

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