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The one thing I don't understand is how the original posts were driven into the river bed. You have to deal with the current, deal with the fact that wood float

The one thing I don't understand is how the original posts were driven into the river bed. You have to deal with the current, deal with the fact that wood floats, deal with a long post, have to have a means of driving it down far enough, etc. I imagine that nowadays they'd use a pile driver on a huge barge with engines that can automatically compensate for the current, but I can't imagine what the equivalent was back then.

baq 6y ago
The thread mentions wooden piers and low tech pile drivers.
nyghtly 6y ago
Maybe the original posts didn't need to be that deep--just deep enough to be used as scaffolding for the wooden version of the pile driver to be set up. They may have also taken advantage of fair weather and seasonal changes. During the dry season, the river would be lower and easier to work with.
- m4rtink 6y ago
  IIRC the water under the bringe is actually behind a weir (to aid river navigation). If the weir was already there back then, they could temporarily open it up and significantly lower the water level.
sradman 6y ago
Good question. The video shows the first posts floating in air across the river and dropping magically in-place. These posts are then connected into a kind of scaffolding for the caisson [1]. A pile driver is built on top of the scaffolding that is used to drive the remaining posts that make up the caisson wall but they don't show what powers the pile driver (men?) nor how it is moved post to post along the scaffolding. A water wheel is used to lift the water out of the caisson. The posts are small compared to modern piles so they will not be overly buoyant. Modern piles are core structural components that are used instead of a caisson so they are quite big. [1] https://en.wikipedia.org/wiki/Caisson_(engineering) https://en.wikipedia.org/wiki/Caisson_(engineering)
01100011 6y ago
You could pre-soak the wood so it's less buoyant, and hold a barge in place with ropes to the riverbanks. I'm not saying that's how they did it, but that's what I would try if I were them. You'd also want to pick the right season when the water flow was the least. You might even be able to dredge a channel so that the water is directed away from the position of the supports. I doubt they had a means of controlling the river flow back then, so I doubt they could have redirected the river into a temporary side channel, but that could also help if possible.
deleted 6y ago
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baq 6y ago

The thread mentions wooden piers and low tech pile drivers.

nyghtly 6y ago

Maybe the original posts didn't need to be that deep--just deep enough to be used as scaffolding for the wooden version of the pile driver to be set up. They may have also taken advantage of fair weather and seasonal changes. During the dry season, the river would be lower and easier to work with.

m4rtink 6y ago
IIRC the water under the bringe is actually behind a weir (to aid river navigation). If the weir was already there back then, they could temporarily open it up and significantly lower the water level.

sradman 6y ago

Good question. The video shows the first posts floating in air across the river and dropping magically in-place. These posts are then connected into a kind of scaffolding for the caisson [1]. A pile driver is built on top of the scaffolding that is used to drive the remaining posts that make up the caisson wall but they don't show what powers the pile driver (men?) nor how it is moved post to post along the scaffolding. A water wheel is used to lift the water out of the caisson. The posts are small compared to modern piles so they will not be overly buoyant. Modern piles are core structural components that are used instead of a caisson so they are quite big. [1] https://en.wikipedia.org/wiki/Caisson_(engineering) https://en.wikipedia.org/wiki/Caisson_(engineering)

01100011 6y ago

You could pre-soak the wood so it's less buoyant, and hold a barge in place with ropes to the riverbanks. I'm not saying that's how they did it, but that's what I would try if I were them. You'd also want to pick the right season when the water flow was the least. You might even be able to dredge a channel so that the water is directed away from the position of the supports. I doubt they had a means of controlling the river flow back then, so I doubt they could have redirected the river into a temporary side channel, but that could also help if possible.

deleted 6y ago

[deleted]