A Robbins TBM

History of the Tunnel Boring Machine

Fred Hapgood

By the middle of the 19th century Western civilization was at the peak of its intoxication with railroads. Everywhere dreamers were bent over maps, drawing lines. As Walt Whitman wrote ...

Lo, soul! seest thou not God’s purpose from the first?
The earth to be spann’d, connected by net-work,
The people to become brothers and sisters,
The races, neighbors, to marry and be given in marriage,
The oceans to be cross’d, the distant brought near,
The lands to be welded together.

Alas, over and over these lines, and therefore these dreams, would bump into a mountain, or worse, a mountain chain, such as the Alps. Building over or around these obstacles was expensive and time- consuming. Logical minds yearned to poke straight through. Alas again, that meant tunneling, and the bill for tunneling was even higher. Tunneling by its nature offered only a tiny working area, not much larger than a bed sheet. Only a handful of people could labor within it at any one time, and much of every shift was wasted wrestling tools and work product out of each other's way. A project in Massachusetts at this time took twenty years to go five miles, and while that was worse than average, the famous formula T(ime) = M(oney) made tunneling costs appalling everywhere.

Bright engineers on two continents had the same thought: maybe their grandfathers would have had to tolerate such frustrations, but this was the 19th century, the acme of human progress, when science and engineering could be counted on to triumph over every sort of obstacle. The fix was obvious: just build a big machine. Amplify the power of labor. Bring the industrial revolution underground. How hard could it be?

The first to step up was a Belgian engineer named Henri- Joseph Maus, who in 1845 got the King of Sardinia to approve construction of the first railroad connecting France and Italy. Maus had an international reputation in mining engineering and the self- confidence to match. He shrugged off the idea of running a line up and over a pass, insisting that the right idea was to go straight through, specifically, through Mt. Frejus, near the famous pass at Mt. Cenis.

This must have raised eyebrows. A tunnel following the route Maus had in mind would have stretched for 40,000 feet, a highly implausible distance given the technology of the time. In this era the tunneling cycle ran as follows: drill holes in the face, pack them with gunpowder, light the fuse, run around a corner, wait for the explosion, run back carrying bracing timbers, hope you could hammer them into place before you got killed in a roof collapse, and shovel or toss the rock fragments into carts for removal.

The problem was that detonating gunpowder in a confined space saturated it with toxic fumes, so all this activity depended upon sucking the air polluted by the previous blast out of the tunnel in a reasonable length of time. Maus' tunnel was way too long for the ventilating technology of the time to deal with. Maus had of course thought of this: he planned to dispense with blasting altogether with the world's first tunnel boring machine,

Maus' "mountain-slicer," as it was dubbed, took shape in an arms factory near Turin in 1846. It was big and complex, larger than a locomotive, bristling with over a hundred percussion drills, all set in a forest of cams and shafts and gears and springs. Functional or not, it was enormously satisfying to contemplate, and tourists came from near and far to admire it as a monument to the age, more as a piece of art than a tool.

Of course some of those visitors appraised the machine more as a tool than as art, and some of those carried away nagging doubts. The enormous levels of power required to drive the Mountain Slicer were generated outside the tunnel and carried to the working face via mechanical linkages. The deeper the tunnel proceeded, the more of these linkages would be needed; the more linkages, the more power would be lost to transmission inefficiencies. It seemed as though eventually the Slicer would stall out. The ever- confident Maus felt he could fix on the fly whatever problems cropped up, but the doubters were not convinced. After the political convulsions of 1848, which left Europe feeling less optimistic and expansive in every sphere, Maus' funding was pulled. (Ten years later a tunnel was built close to Maus' route, but it was done with drill and blast, and relied on vastly improved ventilating technology.)

With variations this story was repeated around the globe year after year: an enormously challenging project, a brilliant engineer, an awe-inspiring piece of machinery, admiring throngs, enthusiastic speeches about the inevitability of human progress, and finally, disappointment. In 1851 Richard Munn & Company of South Boston built a huge machine (for its time; 75 tons) for a tunnel through Hoosac Mountain in northwestern Massachusetts. It jammed before it had gone ten feet. The Hoosac project itself, which had been sold partly on the promise of the machine, bogged down and became something of a scandal. (This was the 20-year project referred to above.) In 1856 one of the most famous engineers in the country, Herman Haupt, announced his intention of rescuing the Hoosac project with another tunneling machine. Haupt was so confident he funded development out of his own pocket. Alas, his machine died before it had penetrated even a foot, leaving Haupt an unhappy bankrupt.

Yet the engineers kept at it. Year after year the Patent Office was peppered with inventions purporting to revolutionize the art. Engineers ransacked the vocabulary of mechanical design: drums, arms, pistons, steam, compressed air. Perhaps it seemed impossible that the industrial revolution could go from strength to strength on the surface while remaining stuck at zero underground. Still, nothing worked.

There were several reasons for this sorry record -- the underground is terrifically hostile to machines -- but one of the more important was conceptual. Many designs were based on the idea of taking a rock drill and scaling it up. Admittedly, there is some surface logic to that: a hole made by a drill does look like a little tunnel. It seems to follow that all you need to do make a functioning tunneling machine is to build a big rock drill. (Edgar Rice Burroughs relied on this idea in his hollow earth series)

As attractive as this is, there is a subtle problem. The amount of energy it takes to cut rock is in part a function of how small the resulting fragments are. The smaller the pieces, the more surface area you create; the more surface area, the more energy required. Drills grind small, which means that a drill competent to hollow out a cylinder ten or twenty feet in diameter would be a real hog, power-wise. Even assuming you could generate and carry such high levels of energy to where it was needed, the forces involved would almost certainly stress your equipment to its breaking or at least bending points. And if you backed off, hoping to protect your machine by exerting a little less power, the machine would seize up against the rock. In the locution of the trade, it would become "muckbound".

By 1930 or so, the message had sunk in. The engineers gave up. According to Barbara Stack, the pre- eminent historian of this technology, "For the next twenty years ... few, if any, patents for rock machines were submitted by engineers, nor were any units built."

Coincidentally, 1930 was also the year that James S. Robbins got his degree from what was then the Michigan School of Mines (now Michigan Technological University). Robbins would have been surprised to be told he was going to have a role in this history. According to his son Richard, he knew nothing about the history of tunnel boring machines, and of course would have had no reason to know it, since by then TBMs were generally assumed to be a dead end. For the next fifteen years he punched his ticket around the industry, doing hard rock mining in California and gold placer mining (i.e., washing or dredging river sediments) in Alaska, and so on. After the war he set up in Illinois as a consulting engineer for the coal industry.

In 1952 Robbins welcomed a tunneling contractor named F. K. Mittry to his office. It is an integral part of this story that the people who dig tunnels were and are a different breed than the contractors who throw up hotels and office buildings. First, tunnel construction is highly stressful, both physically and mentally. The working area is tiny, the lighting is usually terrible, there is water everywhere, and the constrained dimensions mean you are generally about two inches from having your arm torn off by some enormously powerful machines. The medium, the ground, might switch phases instantly to anything from anything, from tough limestone to water- saturated gravel to sand to granite to mud, and any of those changes can plunge an excavation into disaster, either by flooding out or collapsing. While the money was excellent, the risks of bankruptcy or injury or death were higher than normal people like to bear (which was why the money was excellent). Tunneling selected for risk- tolerant, larger- than- life characters who liked long odds and big bets and could endure serious physical stress for long periods.

Mittry was just such a character (and for that matter, according to Richard, James Robbins was a bet-the-company, dam-the- torpedoes, guy himself). He had just won a bid to dig a water diversion tunnel for a dam just outside Pierre, South Dakota. As it happens, the bedrock around Pierre was so riddled with cracks that geologists had a specific label for it: Pierre shale. The fragility of Pierre shale made it very scary stuff to blast in, since you never knew what would end up falling on your head when the charges went off. In any other profession people figure out solutions to problems like these before they sign the papers, but this was tunneling. Mittry had just gone ahead and bid, figuring there would be plenty of time to worry about Pierre shale if he won. Now he had won, and was visiting consultants, shopping for ideas. It is a measure of how intently he was scanning the ground that he had come knocking on the door of an expert in coal mining machinery.

Still, Robbins had an idea for him. The mining industry had just begun working with a technique for cutting coal that used no blasting. The idea was to push a group of metal fingers or picks, like the tines of a fork, into the coal face and then rotate the group, scoring deep circular cuts into the coal. Freely rotating "wedging wheels" or "bursting wheels" were suspended between the tines; these shattered the weakened mineral off the face. The head carrying this pick and wheel assembly would rotate once, then retract, the coal would be shoveled up, and the process would repeat.

Of course the application contexts were very different. Just to begin with, tunnels have to be dug to a much higher degree of path precision than a mine, and the dimensions were totally different. However Mittry was low on alternatives and commissioned Robbins to build a machine based on the pick and wheel idea. He took delivery in 1953.

Like all such machines, Mittry's Mole (as it was called) was impressive to look at: 125 tons, 90 feet long, with a diameter of almost 26 feet. Unlike its predecessors, it was impressive in performance as well. The rotating plate shattered the rock like so much peanut brittle, pushing the tunnel out at rates of up to 160 feet in 24 hours. This was a breath-taking number, almost ten times faster than most contemporary drill and blast projects. Robbins might not have built the world's first TBM but he had done better: He had built the first one that worked. He had beaten ten decades of the profession's most famous minds, and done so emphatically.

Such a feat begs for a moral. Perhaps the lesson is that important innovation is not just a matter of ambitious vision or engineering research in academic institutes; perhaps sometimes advances are made when good engineers are tightly focussed on the specific problems of a specific client. That's a plausible inference and soon it was tested. The success of the machines on the Pierre project (Mittry ordered several more and they all performed wonders) led to a small flurry of contracts. When those machines went into the field, they died in all but the softest rock.

It turned out that Robbins had been lucky: the same properties of Pierre shale that had made Mittry reluctant to blast, that had made him so open to alternatives, also made the rock a perfect medium for Robbins' technology. The rotating head had shattered the rock so effortlessly because, from a geomechanical point of view, it might as well have been glass. Few contractors were lucky enough to find such accommodating material on their jobs.

In a sense the curse of the TBM had returned, but this time there was a big difference: a number of engineers: Robbins, his crew, Mittry's crew, the visitors to the Pierre site, had seen a tunnel boring machine work the way it was supposed to. It was one thing to look at blueprints or listen to inspirational speeches or gaze at a machine sitting quietly on a factory floor, and another to see a radical new idea -- basically a prototype -- go buzzing through the ground like a terrier after a rabbit. Robbins now knew in his bones that TBMs were a very big deal, for all the problems that no doubt lay ahead. He started James S.Robbins and Associates (later, The Robbins Company), the first company dedicated exclusively to the manufacture of tunnel boring machines.

One of his early projects was for a sewer in Toronto. The headache here (there was always a headache) was that the drag picks kept hitting hard rock and snapping off, which meant shutting the machine down for maintenance, over and over, wasting time (Not to mention that the drag picks themselves were not cheap). Robbins kept searching for the open door his gut told him was there. One day he decided to strip the picks off the rotating head altogether. That was counter- intuitive, since the theory was that the picks were primarily responsible for the cutting, with the discs basically just cleaning up. But the engineer's intuition proved out: the TBM ran just as fast as before, only without the pit stops. It turned out that the bursting wheels, which now started to be called "cutter" discs or wheels, had been doing the real work all along.

In retrospect it is easy to see why. Every natural rock is riddled with cracks and flaws on several scales. When the cutter wheels pushed down on the rock the compressive tension introduced thereby concentrated around these weaknesses, with most of the compression organized around the worst flaws. Exert enough pressure and the cracks will extend into the medium. When the wheels roll on, the cracks spring open, splitting the rock yet further. All this happened in order of weakness: making the bigger flaws even bigger. The difference between cutter wheels and drills was like the old story about a skilled jeweler and an amateur: the professional knows how to find and exploit the natural flaws in the gem, and so can make his cuts with a few taps. The amateur has to hammer away all day. Cutter discs enormously improved the efficiency with which energy could be channeled into cutting rock.

Progress tends to be made quickly in the early years of a technology and the Toronto project was important in a second respect. The most taxing and time-consuming part of tunneling is not breaking the rock, but shoveling the fragments into railroad carts and pulling the carts away from the face. For the Toronto machine Robbins set up an ingenious system of buckets that rotated with the cutter plate, scooping the "muck" up off the floor and dropping it on a conveyor that carried it back for disposal. With this bucket-and-conveyor system Robbins had extended the automation challenge another step: the tunnel boring machine had become a tunnel-boring- and- muck- extraction machine.

By the late 50's the TBM had developed to a point where Maus or Haupt would have recognized it as the embodiment of their dreams. When the machines worked, which granted was by no means all the time, they tunneled at two to three times the rate of drill and blast through the same ground. Such speeds represented huge savings. In theory, at this point the contracting and client community would have recognized that the day of the revolution was at hand. A better mousetrap had been invented, and the world should have beaten a path, etc.

In reality nothing of the sort happened. Most of the contractors stuck with drill and blast. They had several reasons for holding back. Up till then tunneling had been a pay- as-you go operation, with low capital and high operating costs. TBMs had to be paid for up front and were not cheap (about a million and change). In the terms of the trade, they imposed very high mobilization costs. That needed some serious adjustments financially.

Most important, the machines were not reliable. Humans may have been slow, but if you put a crew underground you could pretty much bank on getting at least some footage every day. A TBM went faster when it was going, but when it broke down you might have to waste days waiting for Robbins to fly in a part or an engineer. Or you might need to disassemble it and pull it out of the tunnel to do the repairs. If it hit the wrong ground it could literally shake itself to pieces. In the very worst case, where the TBM had to be abandoned altogether, the tunnel would have to be completely rebuilt to accommodate human crews. This would be disastrous for a contractor working under a serious penalty clause. True, tunnelers were gamblers, but even gamblers have their preferred ways of risking their money.

Finally, in 1958 James Robbins died in an airplane accident. This was the worst possible time for the struggling new technology to lose its Moses. Contractors might not have known anything about TBMs, but they knew, liked, and trusted Robbins, who was skilled, ingenious and knew the business. When he died contractors had no one to turn to. Richard took over the company, but he was a young man, only out of Michigan Tech for a couple of years, and an unknown face in a community that valued experience above all.

The company swung from client to client until the late 60's, when the technology got lucky again. At that time Chicago announced a humongous tunneling project, the biggest in history, amounting to billions of dollars and decades of steady work. (As of today, the project is scheduled to wrap up by 2012 at the earliest.) Every tunneling contractor in the country scrambled for the details. And down there in the fine print they found something hair- raising: no contractor was going to be allowed to bid on the project unless he brought a TBM to work with him.

Chicago's problem was that every time a rainstorm passed over, which if you know Chicago you know is not rare, its waste treatment plants would overflow, dumping Chicago-sized volumes of untreated sewage into Lake Michigan. That effluent would then travel through the rest of the Great Lakes, entertaining communities in two countries.

Eventually the level of outrage mounted to such a pitch that the city was persuaded to build a vast system of holding tanks large enough (fifteen billion gallons) to hold the rain runoff until the treatment plants could catch up. More than a hundred miles of tunnels were going to be needed to connect the sewers to these tanks. With drill and blast a project this size would take forever, plus it could not be overlooked that some of those tunnels were going to located under politically sensitive communities, who tend not to like the process much.

On the one hand the tough bedrock that ran under the city was right at the edge of what the TBMs of the day could handle. On the other, a technology that held out any chance of getting the work done in a working man's lifetime was just irresistible. Public works is a famously risk- aversive profession, but this time the city engineers decided to throw the dice. To overstate slightly, from a contractor's point of view they imposed a requirement that no one could meet for a job that no one could afford to sit out.

All across the world the big construction equipment companies, like Hughes Tool and Krupp of Germany and Ingersoll Rand, set up their own R&D operations, competing with each other to make the biggest improvements fastest. "When the project began, the hardrock tunneling record was about 600 feet/month," recalls Howard Handewith, who worked in Chicago and is now a tunneling consultant based in Seattle. "Whenever we had a month of more than a thousand feet we had a party. We had some humdinger parties." (Tunnelers are famous for their parties.) Gradually the machines grew tougher and faster. 1500 ft/month became routine, then 2,000. "This is where the TBM industry grew up and cut its boring teeth," Handewith says. "So to speak."

Today a serious TBM often turns in a production rate of 4,000 ft/month. The newer models come with automatic lining installers, with a robot arm that picks up pre-cast lining segments and clicks them into place around the freshly created interior walls like so many Lego bricks. Such machines integrate all the functions of tunneling into a single device. They can cut through almost any kind of rock and often carry high-tech imaging devices that allow them look ahead. Some are more than forty feet in diameter.

There are now probably around 120 of these splendid machines working at any one time around the world. This number reflects not only the domination of tunneling by TBMs but the increasing reliance of the society on the underground's virtues: primarily the huge amount of space down there. Almost every conflict between surface uses (for instance, between widening a highway and open space) can be dissolved by putting one of the proposed uses underground. You never run out.

The development of TBMs is nowhere near to plateauing. Right now TBMs are all hand-made to specific project specs and geologies. At some point in the near future the industry expects to achieve the holy grail of TBM design -- a universal machine, powerful and versatile enough to handle any job. This will lower costs both by standardizing manufacturing design and improving the market for used machines. Improvements in materials science will soon allow cutter wheels and their bearings to be built of a supertough and microscopically flawless material that will allow the machines to run for hundreds of miles between pit stops. Finally, it should soon be possible to control the machines from the surface, eliminating all the expensive features and procedures now needed to keep humans safe. Small tunnels are already dug this way.

These improvements will open a new era of big dreams -- a Korea- Japan tunnel, a Taiwan-Chinese mainland tunnel -- but the biggest dream of all is the world subway. A maglev in an evacuated tunnel can crank to any speed you like: thousands of miles of hour or more. You can't do this in an airplane; the costs of fighting all that air resistance would be intolerable, and even if they weren't, surface communities would not accept a daily bombardment of dozens of sonic booms. (Underground trains are a lot harder to hit with a shoulder-fired missile, too.) In a hundred years we might have built a system in which every major city in the world would not be more than an hour's trip from any other. Nothing would be more appropriate at its dedication than a stirring delivery of Whitman's poem.