4 Wednesday July 10, 2013

Beneath our streets giant ‘moles’ will be munching away at the earth to carve out 26 miles of tunnels for Eu-rope’s largest construction project worth £16billion.

After being kitted out with orange clothing complete with hard hat, glasses and gloves, and sitting in on a safety briefing, I stay close to construction manager Rob Gordon as we enter a big lift lowering us 40-metres down a shaft at Stepney Green.

Above ground, the location of this Crossrail construc-tion site could not be more peaceful with animals graz-ing at Stepney City Farm and children playing at nearby Sir John Cass School.

Rob emphasises that they have only had one noise complaint from nearby resi-dents and that all the activ-ity is underground. Lorry movements to and from the site are restricted to outside school hours.

As we step out from the lift below we are faced with immense activity as I find

myself inside one of the larg-est mined caverns ever con-structed in Europe.

Flashing red lights warn of moving vehicles, cranes, and skips unloading cement and carrying excavated earth as we stand between the eastbound and westbound caverns. About 7,500 cubic metres of soil was dug to create the eastbound cavern and 9,000 cubic metres for the westbound cavern.

TechniqueStepney Green will not be a stop on the Crossrail network but it is unique among the construction sites as this is where the line coming from Whitechapel will branch out in two directions – one head-ing to Shenfield via Stratford and the other towards Abbey Wood via Canary Wharf, Cus-tom House and Woolwich.

Tunnelling machines Eliz-abeth and Victoria are ex-pected to break through here in October – one into the east-bound cavern and one into the westbound cavern.

Two other twin machines, which will be named in a competition, will be coming from Pudding Mile Lane and are expected to arrive here in August.

The caverns are five metres apart – 35 and 40 metres deep – allowing the tunnel to Strat-ford to run under the route to Canary Wharf as they cross each other.

The tunnels are being made using a technique called sprayed concrete lin-ing rather than letting the giant boring machines carve their way through.

Rob explained that it took two months to get the texture of the concrete right.

“Normal concrete is a bit like scrambled egg whereas this stuff is a bit like a souf-fle – it is very sensitive, you need to get all the constituen-cies right. It’s got additives, microsilica and steel fibres.

“Normal concrete takes longer to settle, which is fine if you have got a supported building, but we need to achieve an inner strength or

the cement won’t stick to the tunnel walls.

“The mix is made off site because of the school and residential homes nearby and dispatched over. It then goes through a special pumping unit, which sprays the concrete out with an ac-celerator at the nozzle.

“The reasons these tech-niques are employed here are because of the geology of the cavern itself. It’s a bit

of a trumpet that gets larger and larger. London clay is soft like cheese and ideal for tunnelling.”

While the cement is being sprayed on the walls of the westbound cavern, a water-proof lining is being fitted to the floor of the eastbound tunnel, allowing water to drain away.

The £500,000 contract to build the Crossrail caverns was awarded to a Span-ish-Irish venture, Draga-dos/Sisk JV, and the highly skilled workforce, which includes civil engineers and miners, has come from across the world.

Rob says: “Most of the guys here have been doing this type of work for at least 20-odd years.

“They may have worked on the new stations at Tot-tenham Court Road, King’s Cross and Heathrow, and before that the Jubilee Line and Channel Tunnel or else-

where in the world. Cur-rently we have about 30 peo-ple on site but at one point we had about 40.”

The site operates 24/7 with 12-hour shift. A longer weekend allows workers from places such as Wales to return home to see their families while others have settled within commuting distance.

A £13m Tunnelling and Underground Construction Academy, part-funded by Crossrail, was set up in Il-ford after it was recognised that there was a skill short-age for future projects in this country.

Once I have surfaced from underground, I’m taken with our photographer on a minibus to the nearby Pud-ding Mill Lane Portal.

As we are lowered in a basket, offering a view across to the Olympic Park at Stratford, a very different construction site is unveil-

My journey into a subterranean world of activityReporter Else Kvist pays a visit to Crossrail sites at Stepney Green and Pudding Mill Lane to discover the work going on underground

Tunnelling in Stepney Green that will form the Crossrail link

Crossrail

London clay is soft like cheese and ideal for tunnelling

Huge machinery at the Pudding Mill Lane site Pictures: Isabel Infantes

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Wednesday July 10, 2013 5

Tunnelling machines

Eight boring machines will be used to construct the new tunnels.

Each is manned by a 20-person ‘tunnel gang’ working in shifts.

As the machines move forward, precast concrete segments are built in rings behind – 250,000 tunnel segments will be used to line Crossrail’s tunnels.

4.5 million tonnes of excavated material from the tunnels will be shipped to Wallasea Island in Essex to create a 1,500-acre RSPB nature reserve.

ing itself before our eyes. Inside a box-shaped hole,

16 metres deep, one of the giant boring machines is al-ready in place underground waiting for take-off to the cavern at Stepney Green.

Its twin machine is cur-rently going through final factory testing in Germany before it will be dismantled and shipped over.

It is expected to arrive on site in about two months when it will be put together.

Construction manager Frank Jenkins explains that each of these beasts costs £10million.

Each machine is about 150 metres long and weighs 1,000 tonnes and on average creates 100 metres of tunnel-ling a week.

He said: “Whereas the construction method at the Stepney Green cavern is more traditional mining – using traditional excava-tors to dig away against

the ground before spraying on the supportive concrete – here we use the tunnel bor-ing machines.

“It’s basically like a huge mole. At the front of it there is a cutter disk which rotates about three times a minute and grinds away at the clay and the chalk and it gradu-ally gets pushed forward by hydraulic rams creating rings in the earth.”

Though computerised, a driver sits inside a control panel at the front of the ma-chines to monitor progress.

Their route has been care-fully planned to avoid any obstacles such as water pipes and to stay clear of build-ings that may not withstand movement in the ground.

Once the machines reach Stepney Green they will be lifted out and taken by police convoy to the Limo site at Canning Town before being put to work again as Cross-rail takes shape.

Else Kvist is lowered into the construction site at Pudding Mill Lane

Frank Jenkins

The Crossrail site at Pudding Mill Lane

The Crossrail project A 73-mile (118km) railway will link

Berkshire and Buckinghamshire via Greater London to Essex with 26 miles (42km) of new tunnels.

The estimated cost stands at £16billion.

Work started in 2009 and there are 8,000 people working across 40 construction sites.

There will be 37 Crossrail stations – the line will bring an extra 1.5

million people to within 45 minutes of central London.

The first services will start through the tunnels in late 2018.

An estimated 200 million annual passengers will use Crossrail.

Crossrail will replace the trains run by Greater Anglia through stations such as Forest Gate and Manor Park. These trains will remain on the surface before branching off on to a new track and entering the tunnel at Pudding Mill Lane.