Before the Brooklyn Bridge (begun in 1870 and opened 1883) became its incredible self, there was a lot of King-Hell work to be done before the recognizably visible bridgey part could be started. Amidst all of the thousands of bits that had to be figured out before a stone or cable could be moved, before the bridge-builder John A. Roebling (1806-1869) could begin to build, he had to construct the gigantic towers which were the great heart of the bridge on solid footing in the East River, and in order to that you had to get to the bottom of the river and then dig from there. Roebling found the solid that he needed, but it was 80 and 40 feet below the river (on the NY and Brooklyn sides), and so it came to pass that Roebling became one of the few U.S. experts in building the apparatus that would allow you to dig down under the bottom of a river. (Roebling became an engineer at a time when there really weren’t very many of them, and the profession was quite small–according to the U.S. census there were only 512 in the U.S.; in 1880, when the bridge was nearly completed, there were 8,600. This number expanded to 45,000 in 1900 and then 230,000 by 19301.)
He created what was basically an upended box, an enormous, 180’x120′ (with a 9′ ceiling that would be 6.5′ at the end) half-city-block/half acre open-bottom box, called a caisson2. The idea was that as it was sunk to bedrock the entire structure would be braced with hundreds of thousands of bricks and then filled completely with cement. That would be the base for the 30,000 tons of masonry blocks (each about 4-7 tons) that rested on top of the 15 layers of massive timber ceiling that rested upon the brick and cement that sat on bedrock.
In the course of excavation the caisson would be filled with pressurized air, and then with its various modes of entry it would accommodate three shifts of about 80 men inside it, shoveling away at the muck and picking away at boulders, digging their way into the river bottom. (Soon enough they would be blasting the boulders in the pressurized air compartments of the caisson, encapsulated by timbers waterproofed with highly combustible materials that were covered by pitch and protective layers of this and that, but that is another of the very many engineering stories that could be told in depth and not to be included in this short note.)
The conditions for work were oppressive, and the pressurized air was difficult to work in and had long-term ill-effects on the body for some, the contrast between light and dark was very stark and difficult with hard shadows, the workspace demanded an immediate body-soaking sweat, the noise of the general work (excepting the blasting and boulder-breaking) was “very considerable”, the muck and water was occasionally a foot high, and the work itself was very physically demanding. There were over 2500 men who worked in the caissons over the 10 months that they were in use, which according to David McCullough in his excellent The Great Bridge3 meant there was an enormous turnover, 100 men a week…and no small wonder. All for $2/day, which was a little better than standard pay for laborers (and equal to about $60/day in 2017 dollars so far as I can reckon, which is sorta/kinda minimum wage for 2008.)
- [Image Source; Engineering, 1873]
So here they are, the guy on the right is hauling the muck to an elevator shaft at right (more visible in the full version of the woodcut, following), while another fellow shovels, and a third man strands there surveying the scene with arms folded in a pose recognized world-wide at construction scenes. The little squares above them show the cross sections of one row 12″-thick lengths of cut lumber (laid on top of another layer of the same running at a right angle, making 15 layers in all) on top of which stone would be placed.
It should be noted in fairness that the supervisors hardly leaned on a shovel or struck an heroic pose in the Brooklyn Bridge construction. Washington Roebling, the son of John A. Roebling and who inherited the project after his father’s very untimely death in 1869 and who was one of the best-suited men in the country to take on the job, spent many weeks in the caissons doing whatever he saw fit to be done. He was one of the relatively few workers there who was overtaken by the demands of the pressurized air, and spent the rest of his life (he died in 1929) dealing with the aftereffects of it.
There were air shafts and elevators and pneumatic tubing to pull out excavated earth, and as the workers dug down, the caisson would sink, and with each movement enormous blocks of granite would be placed on the top of the caisson to help it sink further. And so this would be the process, digging down through a silty river bottom, pulling out the very heavy muck, the caisson moving down as the earth was removed, continuing the process until bedrock was reached. The caisson movement though proved to be a lot more involved than the initial design, where the edges of the thing were supposed to eat and push their way into the earth as ground was removed from around the base, with the enormous tonnage above providing the weight to push the whole thing. But it really didn’t work out that way, and the caisson(s) for the most part didn’t work their way into the riverbed. What happened was that numerous chock blocks were place and large hewn timbers place on top of them to the caisson’s ceiling. And then, once the river material was removed from the perimeter to a certain depth, the blocks would be knocked out from underneath the support, and with practice, the entire structure would set into place, moving down. And then the process would begin again, over and over.
This is another cross section of the caisson, followed by a detail showing the blocks:
- [Image source, for the images immediately above and below: W.A. Roebling, Pneumatic Tower Foundations of the East River Suspension, [the caissons of the Brooklyn Bridge] New York, Averell & Peckett, 1873. The full text is available from Lehigh University http://cdm.lib.lehigh.edu/cdm/ref/collection/bridges/id/1406]
And the blocks and supports, the blocks being knocked out once all of the mud and stone had been removed from the circumference of the caisson:
And then, it was all filled in, more weight was added to the top of the caisson, until that special engineering sweet spot was reached that allowed you to start building the bridge’s towers from which the bridge span would be suspended.
This was a very difficult job and absolutely vital job, not the least of which was the problem of decompression sickness, which affected many dozens of workers, and which was not well understood.
Another image, this from The American Cyclopedia, showing the caisson at a more developed stage, and feeling that much more suffocating, and I think communicates the idea of extreme weight a little better than the others:
- [Woodcut/drawing illustrating caisson used by W. A. Roebling in the construction of the Brooklyn Bridge. The American Cyclopædia, v. 3, 1879, p. 557 (Fig. 2).]
I really haven’t gotten to the most difficult jobs on the bridge. Almost at the very end of the work on the Brooklyn side there was a fire in the caisson. Up until this point there had been a number of small fire that were quickly extinguished. But nearly at completion a worker managed to ignite one of the combustible materials used to sheath the ceiling, and a small section caught fire. Given the pressurized oxygen and other factors the fire progressed to An Enormous Situation. Long story much shortened, the fire was thought to be put out until after one of the continuing series of investigation in making sure that the fire was out revealed that in fact it was not–to make matters worse, it was mostly invisible and smokeless. Many complications and complex solutions later, the fire definitely extinguished, the time had come to finally repair the damage. The fire had eaten its way through several of the 15 layers of the wooden beamed ceiling, and those damaged parts needed to have the crystalized carbon scraped away so that the then-vacant area of wood could be filled with cement. And here it comes: it fell to 18 carpenters to pull their way as far as possible through the burned-out sections of the ceiling to scrape and chip away the burned parts. That means they were underwater, underground, in a cavernous submerged room with pressurized air, and crawling through wormholes in a 15′-thick wooden ceiling on top of which rested 30,000 tons of stone. That, I think, was the toughest job done on the bridge.
30 workers were killed in various accidents during the construction of the bridge. Many considered that a bridge wouldn’t be safe unless there was some fatal blood spilled over it…and many considered that first victim to be John Roebling himself. He met his end before the physical work had been started on the bridge, killed because of a rookie situation he let himself into, he toes crushed by a ferry which led to tetanus and lockjaw, the old man dying a miserable death. He made notes and suggestions on the building of the bridge right up until the end, through the horrible stiffening of limbs and muscles as a result of the lockjaw. I guess he could’ve been considered the bridge’s first martyr.
And to balance things out a bit, here’s the transverse section of the caisson:
- [Image source: W.A. Roebling, Pneumatic Tower Foundations of the East River Suspension, [the caissons of the Brooklyn Bridge] New York, Averell & Peckett, 1873. The full text is available from Lehigh University http://cdm.lib.lehigh.edu/cdm/ref/collection/bridges/id/1406]
Notes:
I can’t help but include another image of a hard place to work, this one for the Thames Tunnel (from my post here: https://historyofideasblog.com/thesciencebookstore/2012/08/beautiful-technical-illustration.html)
1. Cecelia Tichi, Shifting Gears, Technology, Literature, Culture in Modern America. Chapel Hill, 1987, p 104.
2. “Caisson: in architecture, a panel sunk below the surface in soffits or ceilings. In civil engineering, the term is applied, first, to a hollow floating box, usually of iron, which serves to close the entrances of. docks and basins; and second, to a box-like structure used in constructing or sinking the foundation of piers under water. Of the latter there are at least three different varieties: the ordinary, the bottomless or open, and the inverted, which includes the pneumatic. 1. The ordinary caisson is a large box with bottom and sides, made of timbers or planks, in which masonry is built and sunk to its desired position under water.”–The American Cyclopædia, v. 3, 1879, p. 557
3. David McCullough, The Great Bridge, the Epic Story of the Building of the Brooklyn Bridge, Simon & Schuster, 1972.
For excellent source material see: W.A. Roebling, Pneumatic Tower Foundations of the East River Suspension, [the caissons of the Brooklyn Bridge] New York, Averell & Peckett, 1873.
