It’s a pale grey February morning in Woolwich, east London, and in an enormous concrete hole in the ground, Mary is stirring.

It starts with an ominous rumble, audible over the ever-present thrum of ventilation shafts overhead. Then there’s the rushing of water in pipes, following by the rapidclink-clink-clink, like an umbrella tip striking a steel railing, of flint and chalk and sundry muck flushing down steel tubes and echoing down the tunnels behind us. “When they advance, it’s very noisy,” says Gus Scott over the din. “But in a couple of week’s time the people above it won’t even know it’s there. It’s amazing – most people don’t even realise that we’re right underneath them.”

Scott is project manager for the Plumstead-North Woolwich stretch of Crossrail, the vast new inter-London railway being built beneath the capital. If you live or work in London, or have even visited in the last couple of years, there’s a chance that Scott and his colleagues have been working away beneath your feet, excavating, laying concrete, collectively constructing what is currently the largest engineering project in Europe. Chances are you didn’t even notice.

We are standing in the husk of what will become Woolwich’s new Crossrail station. In 2018, an estimated 40,000 people per day will enter the station, taking escalators down to brand new platforms where Scott is right now, before embarking on shimmering new purple Bombadier trains across London and out as far as Heathrow and beyond, to Reading in Berkshire. At the moment though, it’s not much to look at: a 20m deep grey hole, the length of several football pitches, with a central covered section held up by vast wood-clad concrete pillars. Brown water pools in speckles beneath the slate grey sky, which itself is interrupted only by the copper-coloured support beams and, above that, half-finished Berkeley Homes apartment blocks, targeted at future commuters, going up around the site. The only human touch: a statue of St Barbara, the patron saint of tunneling and mining, in a glass case overlooking the entrance. “It doesn’t look like a station yet, but it will,” Scott says.

The focal point is Mary, the giant, state-of-the-art tunnel-boring machine (TBM) currently 10m deep and churning deeper into the London chalk. Custom-made by the German firm Herrenknecht and named for the wife of pioneering engineer Isambard Kingdom-Brunel, Mary is 110m long, measures 7.1m across, and weighs 1,000 tonnes. There are currently nine men on board, plus a mess room, toilet, a microwave and a fridge. She operates 24 hours a day, and looks like a cross between an anaconda and a freight train. “We’re about 200 metres from the Thames,” Scott explains, pointing a gloved hand North towards the river. “So she’ll be going down over the next couple of months, under the Thames, and coming up the other side at the end of April.”

Across London, eight tunnel-boring machines will be digging up over six million tonnes of earth during this tunneling phase. Crossrail is building 26miles of new tunnels and 37 stations, eight of which – including Woolwich – are being built from scratch. Gus Scott is in charge of just 1.6miles, but that key stretch is the only one that involves tunneling under the Thames. As such, where other sites use earth-pressure balance TBMs, Mary is what is called a mixed-shield slurry TBM.  At the front, the enormous cutter head rotates 3 times a minute, boring through chalk, sand and gravel. Fluids pumped in at the face help control pressure and remove the excavated chalk and clay, before carrying it away in barrel-thick pipes back to a treatment plant in nearby Plumstead. Once it has advanced 1.6m, Mary stops, and an internal factory builds the 6.2m-diameter tunnel around it: eight concrete segments, transported in on a dedicated rail system, are lifted into place by a vacuum-erector. Mary will get through 27,000 ring segments before she’s done. “You then push off that ring for the next advance. It’s a very repetitive process,” explains Scott.

Repetitive doesn’t mean easy. For example: when Gus’s team were digging the southbound tunnel (trains travel on the same sides as cars) with Sofia, another TBM, they had to tunnel only a couple of metres from the North Kent railway line, and directly under the sub-station that powers it, while it was fully operational. “People think tunnels go in a straight line, but they don’t,” says Scott. “You’ve got sewers, utilities, Docklands Light Railway, the Underground – so you’re going under and over. It’s fantastically complicated.” Tunneling under the river, 24m down, also comes with certain risks. “Risk-wise, the catastrophic risk of getting inundation [read: flooding] would be horrendous,” Scott says, matter-of-factly.  “But London’s a great city for tunneling, because so much has already been done. There’s a guy on our team, Peter Birmingham, who’s been in tunneling for 50 years. This will be his tenth crossing of the Thames.”

Scott is in his forties, and a blue gingham shirt collar peeks out from the ubiquitous orange high-vis suit that every worker on Crossrail wears. He has lively green eyes and a chirpy smile, and grey hair pokes out in tufts from his hard hat. Originally from Liverpool, he’s been in civil engineering for 22 years: oil and gas, chemical, biotech, rail. He’s worked on Crossrail since August 2011. Before that, like most engineers in this business, he travelled: the United States, Gabon, Algeria, Turkey.”When my three children were very young I used to work abroad, and I’d come home every couple of weeks,” he says. “It’s a way of life. It’s hard work, but it’s fairly well paid and you get to see the world.”

Now though, he’s delighted to be back in the UK working on such a prestigious project. This weekend there’s an open day at the Woolwich site, so Scott is taking his kids down to see Sofia. “My little boy is six, and he thinks I tunnel with a spade every day. I come home and it’s ‘Daddy! Daddy! Daddy! How much tunneling did you do today?’ And I say, ’10 metres, Joseph.'” He smiles. “It’ll be good for him to see what we’re doing down here.”

Later that afternoon, a group of men in orange jumpsuits cross a busy road in Whitechapel, a few miles away in central London. A bus is honking in the lunchtime traffic. Jules Boyd and Geoff Boyd head down a side road behind the library, before stopping beside a nondescript beige corrugated metal building surrounded by a low blue wall. It’s just over three storeys high and is nestled between the library and a branch of Sainsbury’s; if you didn’t know it was here, you’d probably never notice. “This is quite cool,” says Boyd, the project construction manager for Crossrail’s Whitechapel and Liverpool Street site, pausing between the pedestrians at a blue door. “This is a normal London street. Then you go through this little doorway, and the world changes.”

Boyd goes through the door, heads up a short flight of stairs, through the corridors of a pre-fab building attached to the white steel structure. Then he swings open another heavy metal door into “the shed”. At the centre is a vast circular hole in the earth, 35m deep (that’s about seven Routemaster buses stacked wheel-to-roof) and around half as wide. Scaffolding surrounds the opening, and two short-necked cranes, the type you might see at a ship yard (one for hauling dirt, the other for hauling heavy construction equipment) loom at opposite ends.  At the bottom of the shaft, 13 flights down, Boyd’s mining gang is working on what will become another Crossrail station, along with an array of cross-tunnels and vital chambers. The TBMs have already been through here, and now they are doing the all-important work of widening the chambers, waterproofing them and applying sprayed concrete lining before the next contractors come in and build the station itself.

“Don’t put your hands on this area – you’ll get punctures in them,” says Boyd at the bottom, leaning over to pick up a steel fibre from the wall. The concrete lining, called shotcrete, has the appearance of fire extinguisher fluid, layered in viscous charcoal-coloured ribbons. Tiny, hair-like fibres of carbon-rich steel mixed in make it incredibly strong – nine times the tensile strength of the concrete used in an average home. It’s called shotcrete because it’s fired onto the wall using a remote-controlled spraying robot. “That’s probably one of the big advances in modern-day tunneling,” Boyd explains. “Historically it used to be done with mesh and rebar, like you see on most construction sites. This stuff has an accelerator added in the nozzle, so it starts going hard in a couple of minutes.” With a robot, Boyd’s team can spray around 40 tonnes an hour of concrete onto the walls. “Once upon a time, there would have been a guy holding that, who could probably spray 10 tonnes by hand.”

The chamber that we’re standing in, wider than two trains, will eventually be the largest in the whole of Crossrail. Strip lighting gives the tunnel an orange-grey glow. Dust, sweat and diesel fumes hang thick in the air; the whir of the ventilation system is incessant. Men drive earth movers around the tunnel carrying excavated ground, or spoil. In an adjacent tunnel, two engineers are widening a hole where the TBM has already been through. One, in an enormous steel-armed excavating machine, is smashing through the pre-laid concrete rings, while a colleague guides the arms and measures depth with a laser. Rock and concrete tumbles from the ceiling.

“This will be the platform at about this level,” says Boyd, marking a height a few feet off the floor with his arm. “Then the trains will be lower down. The platforms will be hollow, and the ventilation system will suck out the air from underneath. And obviously you’ll have platform doors, so you’ve got a sealed train side and passenger side. I think all metros are going that way in the future. It’s just safer.”

Boyd, 47, is tall and lean, with an aquiline nose and neatly cut widow’s peak. He has always been in tunneling. His father’s family were carpenters, “chippies – men of wood”. Jules studied maths, physics and chemistry at school, and might have ended up a chippy too, if his chemistry teacher hadn’t suggested mining. “I thought: it’s quite tough, you can go anywhere in the world, you get to use explosives, all that exciting stuff,” he recalls. He applied and was accepted to the Cambourne School Of Mines at the University Of Exeter, and after graduating got a job on the Channel Tunnel at the age of 22. (“Mining engineers make better tunnelers than civil engineers, by the way. You can put that in your article.”) He still lives in Folkestone with his family. “There’s a lot of engineering people around where we live. It stems from the Tunnel.” He took a job in Denmark for a few years, before working on the Heathrow Express (“I was on the bit that didn’t collapse”) and some work in Bratislava, before moving back to the UK to start his own firms. They did odd jobs: sea tunnels, sewage works – until the recession hit and he took a job with BBMV, the contractor he’s now working for on Crossrail.  He’s a good manager, well liked, and proud of what he does. He’s particularly proud of the Tunnel, part of which he passes through on his way to work every morning.

“I still think we should have tunneled all the way to London. If we had a forward thinking government at the time, you could have put the TBMs back in the ground, sent them up to London – boom. Ten years we spent wasting money arguing about HS1 [high speed rail 1]. We could have tunneled it in that time.”

He is, unsurprisingly, a vocal advocate of tunneling schemes like Crossrail. “I think we should tunnel everything. Obviously I’m biased because I’m an engineer, but I’m an environmentalist foremost. Think about it: we don’t chop down any trees – we make land. The Channel Tunnel made a great promontory of land with all the muck that came out which is now a nature reserve. We’re making a bird sanctuary in Essex with the dirt from Crossrail. OK, so the process is quite rough, but you don’t get much visual impact – we’re invisible. It’s expensive, but there are 184 bridges on HS1. You could have done it with just two tunnels.”

Around 40 staff work on the Whitechapel site 24 hours a day, though not all down the shaft. The mining gangs work 12 hour shifts, seven days a week. (After that they have three days off, before seven days on the night shift – a pattern dubbed 7374, and voted in by a democratic process.) “Though usually you’d only spend maybe six or seven hours down,” says Moeen Uddin, a 20-year-old engineering technician. “You’re not stuck down here.” Many of the engineers on Crossrail are young guys like Uddin (the gang call him Mo) – apprentices, graduates. Uddin is working on Crossrail for BBMV while studying for his higher national diploma in Civil Engineering.

A typical day: Uddin gets up at 5am in his flat in Bow that he shares with his brother, a carpenter. He’s a fresh-faced: short black hair, goatee, and has the lean build of someone who’s young and uses their hands for a living. He’ll get into work about 6.30am, have a shift handover meeting with the guys just coming off the night shift, then head down the shaft: excavating, spraying, whatever needs to be done. A spray will take about three hours. Then he’ll take a break and head topside, complete the necessary paperwork, maybe get a bite to eat before heading back down for whatever needs doing that afternoon. On Thursdays Uddin goes to Southend College for lectures; he’s got two more years on his HND, then two more to get his degree, by which time Crossrail will be finished. He loves college “the theory aspect of it fascinates me. It’s interesting to know exactly how things work.” Once he’s got his masters he’ll probably do what the rest of the tunnelers have done and travel the world, working on huge infrastructure projects. The huge new metro – 22 TBMs – being built in Riyadh, maybe, or Qatar, where they’re preparing for the football World Cup. “It’s one of the things that attracts you to it. You do get to travel. I would love to explore different parts of the world. Wherever the work takes you, really.”

Working underground for long stretches with heavy machinery is hard, and traditionally dangerous. Crossrail works to Target Zero, meaning zero fatalities and serious injuries across the entire building phase. Unfortunately, that aim was broken in the early hours of Friday 7 March, a few weeks after GQ’s visit to the Whitecapel site, when a 43-year-old engineer working on one of the Holborn sites was killed by falling concrete during a shotcrete spray on a crossover tunnel.

Despite that tragedy, health and safety measures have transformed tunneling safety into something practically unrecognizable from when Geoff Wilks, the site manager for the Whitechapel dig, started tunneling over 40 years ago. “It has improved over the years, massively,” Wilks recalls. “It’s slowed down a bit, but you don’t want to be tearing away and people getting killed, which I’ve seen.” Wilks is 65 years old “and still raring to go.” He has a grey hair, a thick brush of a moustache and broad, tattooed forearms. (“These hands weren’t built for IT,” as he puts it.) He was born in Guisborough, on Teesside, and started as a miner on the Boulby potash mine in the Sixties, where they sunk shafts 1,600m deep.

“There was a lad who had started on the same day as me, a fitter who had been working in South Africa. A few weeks later he was stood on a stage watching the lads working. A skip cap down and practically took his head off.” Another day, on the same job, a new starter on the mine was stood in the wrong place, “and a skip swung over and smashed him against the side. Killed him. He was only down for 20 minutes, and he was gone. Unreal.” A few years later a good friend was killed when an object dropped 2,000 feet from the surface down a shaft, went straight through his helmet. “So it has got better, yeah.”

Wilks spent ten years in Boulby, before moving to Selby coal field in the Seventies, sinking shafts up to 1,000m. “Then after that it was just going where all the work was. All over England, basically.” In 1992 he took a job in Malaysia, working on a massive hydroelectric scheme – a 17mile hard-rock tunnel. Every six months his wife would bring his daughters over to visit. They loved it. “Most of the older boys worked different jobs all over. There are two or three of them down below now who I worked with in Malaysia,” says Wilks. (Gus Scott, the project manager back at Woolwich, says of tunnelers: “They hunt in packs.”)

These days he manages the Whitechapel site, looking out for the young guys like Mo. He lives nearby during the week, and on Fridays he takes the train back to Teeside to see his wife and daughters, who live nearby with his four grandchildren, who he takes to football practice on Saturday mornings. This is the first time he’s worked directly for a client, overseeing production. “To be honest, I think there’s a little too much paperwork involved in the work nowadays,” he says, carefully. “When I go down there and walk around there’s men stood, which is one of the things I used to hate seeing when there’s work to do. They’re waiting for paperwork to be signed off. But you can’t knock the health and safety side of it, because that has improved over the year.” He pauses at the open face of the one tunnel, where the engineers are widening the TBM tunnel with an excavator and laser guidance, stood several feet from opening. “In my day there would have been men in there with shovels,” he says, indicating the 6.2-metre opening extending into the darkness. Concrete and clay tumbles from the ceiling; dust fills the air and settles on our orange overalls.

Back on the surface, we head back to the Crossrail office across the street from the site. Boyd points out a series of small black plastic nodes on the sides of the surrounding buildings: sensors measuring for any ground settlement caused by the tunneling; grouting can be pumped in underground to compensate. In a few hours Boyd and Wilks will head home, but the tunneling will continue; the night shift will come in and take over. There’s still plenty to be done: putting in escalator shafts, extending the chamber. At the nearby Liverpool Street site, Boyd’s team are tunneling 600m underneath the private Post Office rail line. Down the road in Moorgate, Crossrail engineers are tunneling up between two Northern Line platforms, breaking in so that in future passengers will be able to transition from the underground straight into Crossrail. That work has to be done by hand on the night shift, not to disrupt thousands of commuters passing through every day.

“The guys down there, they work f***ing hard, and they do play hard,” Boyd says, back in civilian clothes. “Historically, it used to be a big hard-drinking industry – it’s not now. But there are some big characters. To put up with that every day for half your life, you need some pretty strong resolve.” Jules and Geoff are both still married, “that’s quite rare in this industry,” Boyd says. “Working away from home puts strains on relationships.”

The station building will be over by 2015, at which point a follow-on contractor will come in to build the station, lay the rail lines and signals. “I don’t want it to end,” says Boyd. “Because then you’ve got to go and find something else.” Not that it will be hard: thanks to recent investments in infrastructure. “You’ve got HS2, Bank station upgrade, the Northern Line extension, Tideways. Crossrail is leaving a legacy of trained engineers. You don’t have to go abroad to work on big projects any more. They’re happening right here in Britain. It’s a boom time for tunneling.”

From 30 metres below ground to thirty floors above it: Andy Mitchell, Crossrail programme director, sits in his office in Canary Wharf, looking out at the London skyline. Mitchell has greying hair, a high forehead, and wears a pin-stripe suit, pink shirt, half-rimmed glasses, and the furrowed brow of someone who has too much to do. “We’re about half way through,” he explains. “We’ve got about a year to go of the civil engineering. All these holes in the ground aren’t for their own sake. It’s all about creating space to build a railway. As of next year we’re a station builder, we’re a railway builder, we’re a train builder – so it’s a very different project.”

Mitchell’s office will oversee the transition between contractors like Gus, Jules and Geoff and the station-builders, the transportation engineers laying track and signaling, and so much more besides. “Soon it’ll be a different set of challenges: getting the train to talk to the signaling system, to talk to the station, to working with the existing rail network…” he smiles wearily. “There are a lot of operational challenges. I defy anyone to describe building 30 kilometres of tunnel under that lot” – he points out to the London skyline, over businesses and docklands, stretching east out towards the Thames estuary – “as easy. Because it bloody isn’t.”

Like most of the senior engineers on Crossrail, Mitchell spent half of his life overseas: petro-chem in Abu Dhabi, design training in France, gold mining in South Africa, six years in Hong Kong building the airport and rail system. So he’s delighted to see the impact on young people.”Through my 20s and 30s if you wanted to get big project experience on a wide range of engineering – civil or any other way – you had to go overseas. You went to the Middle East or Hong Kong. You can do that in London now. That’s just a huge change.”

He’s takes particular pride in what Crossrail is doing for young engineers like Moeen Uddin. “If you look at the age profile of a lot of senior folk – the general foremen, the site supervisors – they are in their fifties, if not older. We’ve got a bit of a time bomb in the industry. There’s almost a missing generation. So to see graduates, and apprenticeships coming in, it’s something the industry desperately needs.”

He still worries: about safety (“the ambition is that everybody gets home safe every day. It’s not easy to do, and not every day goes well”) and diversity (“the number of women in construction is just not representative as a whole of society, and we’ve got a lot of work to do there”). The tunneling may be almost over, but there’s a huge amount of work to go until the first trains hopefully pull away from the Woolwich and Whitechapel stations in 2018.

“You don’t want to make too much noise about it, because tomorrow is another day,” says Mitchell. “But I’m just one of 10,000 people working on this job. And what’s going on out there, what we’re doing between us, is astounding.”

In 2013, London Underground marked 150 years since it first opened in 1863. The target lifespan for Crossrail is a minimum of 120 years. It’s astonishing to think, walking through the tunnels at Whitechapel, or the standing in the vast concrete foundations in Woolwich, that what these men and women are building will still be standing and working in more than a century.  “That’s why we come to work. That’s why we love it,” says Mitchell. He puffs out his chest, and smiles, radiating pride.  “The ability to point at stuff and say, ‘I built that.'”

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