by Roma Agrawal
Marc Brunel was born in Normandy, France, in 1769. As a second son he was expected to become a priest, but he showed more interest in drawing and mathematics than in scripture, and entered the navy instead. Fleeing France in 1793 during the French Revolution, he went to America, where he eventually became Chief Engineer of the city of New York. He then moved to London in 1799, to try and persuade the Admiralty to purchase a new system he had invented for producing pulley blocks. He worked on various projects for the armed forces, developing apparatus for mass-producing soldiers’ boots, and sawmill machinery at the Chatham and Woolwich dockyards. But he came to the attention of the Thames Tunnel Company (after vigorously lobbying its bosses) because of the tunnelling machinery he had invented.
Brunel carried a magnifying glass in his pocket. While working at Chatham Dockyard, he picked up a damaged piece of timber that had been removed from the hull of a warship, and scrutinised the actions of Teredo navalis (the naval shipworm) at close quarters. The worm had two razor-sharp, shell-like ‘horns’ on top of its head, and as it moved, wriggling and rotating its horns, the wood directly in its path was ground into a powder. The little shipworm ate the powdered wood and wriggled a few millimetres forwards into the space it had just created. The powdered wood travelled through the worm’s digestive system and mixed with enzymes and chemicals in its body. The worm then excreted this mixture, creating a thin paste that lined the small tunnel left behind. When exposed to the air inside the cavity, the excretion hardened, shoring up the tunnel. Slowly but surely the worm moved forwards again and again, munching through the wood while creating a strong, lined passageway behind it.
Fully aware of the previous attempts to create a tunnel under the river, Brunel put his genius to work, and came up with a new plan. He realised he could succeed where everyone else had failed by adapting the process he had just observed. He would build his own shipworm: a machine that could tunnel forward and line the hole behind it. But his ‘worm’ would be made from iron. And it would be colossal.
Brunel’s idea was that the device would have two blades, just like Teredo navalis – but that these would be twice as tall as a person. The blades would sit at one end of an iron cylinder lying on its side (and looking a little like a fan we might use in the summer to keep cool, but without the cage). A team of men would push the blades round so that they ate at the ground. Hydraulic jacks would push the cylinder forward. The soil which had been cut away by the blades would be transported backwards manually, like the shipworm excreting wood powder. As the cylinder moved forward, it would expose a ring of ground. To shore this up, bricklayers would lay bricks in a ring using quick-drying mortar to glue them together, creating a cylindrical shaft behind the blades, much like the worm’s waste lining its tunnel. This process – turn fan, remove soil, lay bricks – would be repeated to gradually fashion a strong cylindrical tunnel.
Brunel’s shipworm.
Having sorted out his worm, Brunel now had to find a suitable material for it to burrow into. Obviously, some substances are easier to dig into than others. Take dry sand, for instance. Fill a circular cake-tin with sand, then try to scoop out half of it to create a semicircle. You won’t be able to, because the particles of sand simply collapse into the space you’ve just emptied. Similarly, if you try doing the same thing with very wet sand, the liquid nature of the material causes it to flow into and fill the space you’re emptying. London sits on clay that’s 50 million years old. If this clay is nicely compressed under layers of soil, and not too wet, it forms a fairly stable layer of ground. From an engineer’s point of view this is good to work with, because you can slice into it quite easily, and it’s unlikely to collapse. Put good clay – nicely compressed and not too wet – in a circular cake-tin and remove half of it, and you’ll be left with a perfect semicircle of material. On the other hand, London’s clay can vary considerably: it can be sandy, weak, watery and inconsistent. For Brunel’s invention to work, he had to find good clay.
He hired two civil engineers to investigate in detail what the ground was made of. Paddling around in a boat, they plunged a 50mm-diameter iron pipe deep into the riverbed, then hauled it back out. They then studied the substances that had become trapped in it, looking to identify the different soils inside, and the thickness of each layer. After months of investigating they submitted their findings to Brunel, who decided that the ground was good enough for his plan to proceed without major problems. Before his shipworm could be let loose, however, he needed to burrow deep into the ground.
On 2 March 1825, the bells of St Mary’s Church in Rotherhithe pealed as throngs of people made their way to Cow Court, ready to witness a very unusual sight. In the middle of the yard lay a huge iron ring 15m in diameter and weighing 25 tonnes. A brass band began to play as well-dressed ladies and gentlemen appeared, looking out of place in this rather squalid part of London. Amid cheers from the crowd, Marc Brunel arrived with his entire family, and was presented with a silver trowel, with which he laid the first brick on top of the iron ring. Brunel turned to his son, Isambard, who laid the second. Then followed speeches, drinking and toasts to the arts and sciences to mark the inauguration of the Thames Tunnel. But the joyful crowd had no idea just how much the sciences would be challenged in the months ahead.
The iron ring the crowds could see was like the sharp end of a cookie cutter. Two rings of brick separated by a layer of cement and rubble were laid on top of the iron ring, creating a cylindrical tower just under 13m high. On top of this the builders placed another iron ring, which was linked to the bottom one using iron rods sandwiched between the two brick walls. A steam engine was attached to the top of the 1,000 ton structure to pump away water and remove the excavated soil.
Tunnelling under the river Thames, London.
To use a cookie cutter, we apply the strength in our arm muscles to push it down into the dough. But Brunel’s idea was to allow his brick cutter to sink into the ground under its own weight: it was so heavy that it would naturally move through the soft soil. Slowly but surely, the shaft began to sink a few centimetres a day. As it sank, diggers removed soil from the middle of the cylinder, much as you would remove dough from the middle of a cookie cutter.
After getting stuck once, the brick shaft arrived at its final destination. To create foundations, the diggers dug another 6m below the bottom iron ring. In this space, bricklayers filled in three sides of the shaft and the floor, leaving one face open to the ground. This is where Brunel’s ‘worm’ would be deployed to burrow the tunnel.
While all this was happening, Brunel realised that – unlike a shipworm, which could easily turn its blades – humans didn’t have enough strength to rotate the blades of his tunnelling machine. He couldn’t think of a way to attach a steam engine to provide the power, so instead he came up with a new idea. His solution was to divide the device into smaller sections – 36, in fact – with a single person working in each. He called this enormous machine ‘The Shield’.
Working The Shield, the enormous machine used by Brunel and his men to excavate underground.
It had 12 iron frames, each 6.5m tall, 910mm wide and 1.8m deep. Each frame was divided into three ‘cells’, one on top of the other. The twelve frames were placed side by side to create a big grillage of 36 cells, each housing one worker, and these workers would operate The Shield. At either side of each man in his cell was a set of long rods, spaced at regular intervals from floor to ceiling. These held in place 15 or so planks of wood, stacked one above the other directly in front of the worker, and shoring up the ground in front of The Shield.
Operators in alternating frames (say frame numbers 1, 3, 5, 7, 9 and 11) worked simultaneously. Their task was to remove one wooden board by drawing back the two iron rods holding it in place, and dig out exactly 4.5 inches of earth and put the board at the rear of this new, slightly deeper cavity. They would then push the rods into place to support the board. The next step was to remove the subsequent plank and repeat the process, continuin
g like that until all the wooden planks in all the 18 cells had been fixed into their new positions. Now that these miners had excavated the section of ground in front of them, jacks at the rear of The Shield propelled their cells forward by 4.5 inches.
At this stage, the odd-numbered frames would be 4.5 inches ahead of the even-numbered ones. It was now the turn of the workers in the even frames to go through the whole process of adjusting rods, removing boards, digging into the earth and repositioning the boards. When they had finished, the even frames were pushed forward. The entire shield had progressed by 4.5 inches – the exact distance needed to fit one layer of bricks.
Behind The Shield was another flurry of activity. ‘Navvies’ (as the labourers who built the canals, roads and railways were known, after the word ‘navigator’) removed the excavated soil in wheelbarrows. Bricklayers stood on wooden planks and carefully laid bricks in the 4.5 inch gaps created as The Shield moved forwards. They used pure Roman cement, which dried very quickly and was incredibly strong – so strong, in fact, that when Brunel tested it by building a block of bricks and dropping it from a height, the cement didn’t crack. He even had his workmen attack the block of bricks with hammers and chisels; while the bricks cracked, the cement stood unyielding. Brunel then decided to use this cement throughout the tunnel, despite its great cost (remember that a lot of energy goes into producing pure cement powder, which can be lessened by adding aggregate).
I try to imagine what it must have been like working in the tunnel. Before I’m allowed to set foot on a construction site, I have to pass exams, be trained in health and safety, and put on protective clothing. I walk around doing my job without worrying that I might not leave alive. Conditions in the Victorian tunnel were starkly different: the smell of the workers’ sweat, the tallow smoke and the gas fumes made breathing very difficult – workers often emerged from the tunnel with a ring of black deposit around their nostrils. Flammable gases trapped in the soil were suddenly released and, if lamps were inadvertently brought near them, could catch fire and explode. The air was damp and the temperature rose and fell by thirty degrees, sometimes in the space of a few hours. It was also incredibly noisy – bricklayers shouting for more bricks, iron rods clanging, wooden boards thudding and hobnailed boots echoing through the tunnel. Brunel himself became very ill from over-exhaustion, and was prescribed the only treatment that would work: being bled by leeches on his forehead.
Brunel’s son, Isambard, who was only in his early twenties at the time, became indispensable on the project as the main engineer running the site. (Sophia, Brunel’s elder daughter, was nicknamed ‘Brunel in petticoats’ by the industrialist Lord Armstrong because Marc Brunel, unconventionally, taught his daughter about engineering. When they were children, Sophia showed more aptitude than her brother in all things mathematical and technical – and in engineering – but it was her misfortune to be born at a time when women had no such career possibilities. She is the great engineer we never had.) But Isambard, like his father, was often taken ill. And things were getting worse: the soil conditions were unexpectedly deteriorating, and funds were running out. At one point the whole operation was shut down and the tunnel bricked shut with The Shield inside it. It took six years for the Brunels to convince the Treasury to put more money into the project. The company directors meddled with Brunel’s methods, refusing to obtain equipment he wanted to make the work safer, and pressuring him to work faster despite the risks. The biggest problem, however, was the flooding. The ‘good’ clay that Marc had been hoping to tunnel through was not consistent, and sometimes it disappeared completely, especially as the workers dug directly below the river.
The Thames was basically a huge sewer; all of London’s waste (and many of the city’s corpses) were deposited into it. The soil at the base of the river was very wet and of terrible quality, and the tunnel was being dug only a few feet below the river, right into this base. As The Shield moved forward, digging away at the ground, the soil was often displaced more than it should have been. There was also a weak point in the riverbed between The Shield and the brick tunnel, and if the soil was particularly bad it simply collapsed, sending river water coursing through the passageway.
The first time this happened, Isambard fixed the problem by contacting the East India Company and borrowing a diving bell (a chamber containing a couple of people that could be lowered underwater). In it he went to the bottom of the river, found the leak, and laid a bed of iron rods across the gap, with bags of clay piled on top to seal the hole. Once the water had been pumped away, the digging work could restart.
Innundation of the tunnel and the use of a diving bell to seal the breach.
This, though, was only the first of four major floods in which many men died. Isambard himself only narrowly escaped drowning, suffering his first (but not last) haemorrhage as a result, and being forced to leave the site for a few months’ convalescence.
Despite the setbacks, however, in 1843, after 19 years’ work, the tunnel was finished. Penny-paying pedestrians descended the spiral staircase in the shaft to the tunnel, which in its finished form was spectacular. A line of pillars down the centre supported immense brick arches. Gas lamps lit the passageway and an Italian organ powered by a steam engine played music. Hawkers sold refreshments and souvenirs from little alcoves in the brick walls. In 1852 the first Thames Tunnel Fancy Fair was held, featuring artists, fire-eaters, Indian dancers and Chinese singers.
But only a decade later, as the railways entered everyday life, the tunnel had fallen into disrepute. People no longer wanted to walk through its damp interior, choosing instead to take the flashy new trains. The tunnel became seedy and desolate, the haunt of drunks. In 1865 it was handed over to the East London Railway Company, and by 1869 rail tracks had been installed on the floor and steam trains began chugging through. Today, the London Overground line runs through it. The Rotherhithe shaft, which Marc Brunel managed to excavate so imaginatively, was recently opened to the public and has become a popular tourist attraction. Enter the stumpy circular tower and you find yourself in a cavernous underground chamber containing the remains of spiral staircases, and blotchy, scarred and weathered walls with mysterious black pipes feeding into and out of them. It’s an incredibly atmospheric backdrop to the concerts and theatre performances that take place there.
Taking nearly 20 years to build, and then becoming obsolete just over 20 years after it was finished, the Thames Tunnel might not seem like a success. But thanks to Marc Brunel’s imaginative engineering, we gained access to the underground parts of our cities. The London Underground – the first underground train network in the world – was made possible because of the work of Marc and Isambard Brunel, who showed us how to build structures in very fluid soil.
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To dig their tunnels, the engineers building Crossrail (London’s new train line) have been using a modern version of Marc Brunel’s first and unsuccessful idea. Brunel couldn’t get enough power to rotate giant blades, but electricity has made this simple for us. Instead of a manually operated machine, we use ‘tunnel boring machines’ (TBMs) – which are, of course, anything but boring.
Each of Crossrail’s TBMs – described as ‘giant underground factories on wheels’ – is as long as 14 London buses end-to-end. The front has a huge circular cutter that spins, eating into the ground in front of it. An intricate jacking system pushes the machine forwards. Conveyor belts transport the excavated soil to the back of the TBM and out of the tunnel. A laser guidance system makes sure that the tunnel stays on course. Behind the TBM, a complex array of arm-like devices fix concrete rings in a circle (steel could also be used) to create the tunnel lining.
There’s an endearing tunnelling tradition which proclaims that the TBMs must be named – with female names – before work can start. Crossrail ran a competition to name its TBMs in pairs, since the machines work in twos, radiating in opposite directions, starting from a point. One pair is named after the monarchs of the great railway a
ges: Victoria and Elizabeth. Another after Olympic athletes: Jessica and Ellie; another after the women who wrote the first computer program and drew the beloved London A–Z maps: Ada and Phyllis. Perhaps most fitting of all, though, are the names of the final two TBMs: Mary and Sophia, after the wives of the great tunnel builders themselves, Isambard and Marc Brunel.
PURE
It thrills me to see tourists taking pictures of buildings in a city, because it means that they love engineering – even if they don’t realise it. They admire and respond to the ambition and the imagination that have gone into the design – curved canopies, tall silhouettes and unique facades are carefully selected, framed and frozen in time as the dramatic backdrop to countless photographs taken on phones mounted on selfie sticks. This architectural drama is the romantic side of engineering, and not to be underestimated. Nevertheless engineering is ultimately a response to very practical considerations; often it is less immediately exciting things like soil, materials or the law that are the driving force. A building or bridge might look spectacular; in fact, much of what shapes it can be decidedly unaesthetic.
One of the most influential of these considerations is water, which is such a fundamental requirement for humans that we can’t survive much longer than three days without it. The structures I design are skeletons: until they have water, they are merely uninhabitable shells. I work with other engineers (mechanical, electrical, public health) to make provisions for the skeleton to support its circulatory system: creating pathways through it and making sure that its foundations, core walls and floors are strong enough to carry the weight of pumps and pipes. It’s only when the arteries of water come to life that we create a building fit for the living.
