Working inside a gargantuan underground factory driving a tunnel through the heart of London on the biggest construction project in Europe ought to be fun, but the workers digging the tunnels for Crossrail are used to jokes about their “boring” job titles. Inside the deafening noise and the energy of this 24-hour operation, however, tunnel boring is anything but.
"It's like being in Stargate," says safety co-ordinator Jason Meadows as he prepares us for our trip inside Phyllis, the 148m-long tunnel boring machine (TBM) currently 30m beneath Hyde Park, churning out clay from the end of a tunnel so far stretching 1.5 miles.
It sounds like a ridiculous description while sitting in the plain-walled site office at Westbourne Park, but when you reach the front of the machine it seems the perfect comparison.
Red lasers cut through the air, guiding giant segments of concrete on to the tunnel wall as they are turned and moved by grunting machinery using a vacuum to hold them in place.
In front of that, a giant drill begins to turn, crunching through the ground. We are inching through mud at 25 metres a day rather than being transported through space to another galaxy, and there are old-fashioned white plastic rulers alongside the lasers. But the scale and complexity of the machinery is of sci-fi proportions.
It will be five years before the first passengers travel on Crossrail tracks. When complete, there will be 24 air-conditioned trains an hour, each capable of carrying 1,500 passengers, rumbling under the capital.
And "under" is the operative word; 150 years after the first London Underground train crept through an embryonic Tube system, the city's netherworld is so full of criss-crossing sewers, train tracks, skyscraper foundations, telecoms cables and secret government burrowings that Crossrail is having to go deep to avoid them.
Keith Sibley, the 62-year-old American director of the western tunnels, has overseen the building of nuclear power plants in his home country. But he says cutting a new train line through a "living, breathing city" is the biggest and most exciting venture he has undertaken.
Trying to carry out the project while causing as little disruption as possible to the city and its people is like a complex medical procedure, he says. "When you do open-heart surgery, you can't kill the patient, do the operation and then bring them back to life again."
The London Mayor, Boris Johnson, has been keen to underline the benefits of spending £14.8bn on Crossrail: it will increase the capacity of the city's rail network by 10 per cent, linking Maidenhead and Heathrow in the west with Shenfield and Abbey Wood in the east. Only 15 miles of the 74-mile line will be underground, but with twin tunnels needed to carry trains both ways, that's 30 miles of boring.
Eight boring machines will be used to complete the digging. Five are already under way – there's Ada alongside Phyllis in the west, Elizabeth and Victoria in the east, and Sophia which has started digging out the Thames Tunnel. A few of the workers call them "boys' toys", but there are a smattering of female engineers too.
Unlike the Mole of Thunderbirds fame, Phyllis and her comrades – each costing £10m and manned by a maximum of 20 people working eight-hour shifts –have flat-headed drills that rotate just over three times a minute while scything through the clay. The damp earth is then funnelled away on a conveyer belt that carries it all the way out of the tunnel, dumping it at Wesbourne Park to be taken by train to Essex – where it is being used to build a new nature reserve.
It's amazing to think, as 52-year-old western tunnels construction manager Steve Parker says: "That mud probably hasn't seen the light of day for 900 million years."
The tunnel is lined by 1.6m-wide rings of concrete, each made of eight segments, which take about 20 minutes to fit before the boring machine moves forward on wheels rolling along the concrete it has just laid.
Catching a ride on one of the trains – or "locos" in the parlance of the tunnellers – that lumber the segments and all the equipment needed to fit them down the 6.2m-wide tunnel, it takes us 15 minutes to reach the machine. There, we're met by a mass of metal gantries and barrels of grease for the drill, as well as the cables carrying electricity and pipes filled with coolant water that Mr Sibley calls the TBM's "umbilical cords". The control room, full of buttons and screens, is more akin to a hunter-killer submarine than a mining operation.
As well as a small canteen, the TBM also thankfully contains a toilet – a welcome change from tunnelling jobs of the past. "Twenty or 30 years ago, if a skip came out of a tunnel steaming you knew not to go near it," smiles Mr Parker. The tunnel is not classed as a confined space – which is convenient, as under Health and Safety laws that would mean anyone going underground, from the Prime Minister to The Independent, would have to undertake days of training.
Safety concerns are both serious and copious, nonetheless. Mr Meadows enjoys seeing how wide our eyes become when he teases us that the reason for wearing copper number tags around our necks is so that in the event of a fire our charred bodies can be identified – and fire in a tunnel, he smiles, would rush past us "like Usain Bolt".
In truth, however, the chances of a fire breaking out are extremely low, due, not least, to virtually every material used having been coated in fire retardant. Should there be an emergency, the TBMs used for Crossrail are the first to contain a rescue chamber where workers could shelter. Each person is fitted with a gas mask that explodes out of a pack carried around the waist at the touch of a button.
Nevertheless, it's only after emerging from the noise and the low light that it becomes obvious how intense the working environment is down there. Seeing the light and breathing in the cool air of Westbourne Park is quite a release. But it's easy to see why Mr Parker says he is "passionate" about his 25-year tunnelling career. It's a truly impressive spectacle.
For years, the trade joke has been that if you look up "boring" in the Yellow Pages, the entry would say: "See civil engineering." Looking inside Phyllis and meeting her crew, many a civil engineer thinking about starting a career underground should feel pleased to be given that label.
The boring machine: How it works
1. Rotating cutter-head loosens the earth. Trimay/Hardox-plated and tungsten-carbide-tipped picks and disc-cutters make the tools stiffer than steel and denser than titanium.
2. Screw conveyor moves earth from the cutter head.
3. Rotating arm places segments with millimetre precision to form a ring.
4. Hydraulic cylinders brace themselves on the newly positioned rings to push the machine forward at a force of up to 58,000kN. This is the equivalent to the force needed to lift over 2,900 London taxis.
5. Each ring is made up of eight segments and weighs 22 tonnes.
6. Belt conveyor system removes earth from the machine.
7. Pre-cast concrete segments delivered to the segment feeder. Over 250,000 segments will be used to construct the tunnel walls.
8. Conveyors move earth to the tunnel portal.