> The tagline of the Pile Driving Contractors Association is “A Driven Pile is a Tested Pile” because, just by installing them, you’ve verified that they can withstand a certain amount of force. After all, you had to overcome that force to get them in the ground. And if you’re not seeing enough resistance, in most cases, you can just keep driving downward until you do!
I can imagine that slow static loading could allow sinking whereas dynamic force would not. Soil liquification is a weird thing, analogous to silly putty where it can be soft when manipulated slowly but hard when impacted quickly.
Yeah, it also assume that the pile you're driving can be arbitrarily long and will last forever. They used to be made with trees, for which this is obviously false.
IANAE (No An Engineer), but I think he mentions both the issues of piles wandering off-course, and of unanticipated piling problems causing major budget & scheduling issues.
From a structural PoV, an extremely long piling in soft-ish soil will start having problems with lateral deflection - which it is too thin (relative to length) to resist. Then there's the case of "we think we finally hit bedrock...but what if it's just a big boulder?".
I can imagine cases of pilings running into large underground caverns, or penetrating strata containing water / gas / petroleum under pressure.
Edit: From a quick search...
In some locations, bedrock may not start until >1000' below the surface.
>> Your guess is as good as mine why the same steel shape is an I-beam but an H-pile.
This is because the shapes are different. I beams are typically more slender through the web because the goal is to concentrate mass at the flange for moment capacity because they’re beams and geared towards bending. H piles are thicker in the web with the web thickness usually similar to the flange because the use case requires axial capacity and various constructability considerations. I beams turned into W (wide flange) and S sections in the standard shapes and H beams are called HP sections.
You’ll often see them cross-specified for foundation work but it’s rare that you’d choose an HP section over a more efficient section like a W or S for something “out of the ground.”
Thank you for this. In college, for some reason, i hung out with architecture majors instead of my fellow computer science people. They would talk about "w flanges" when, to me, they meant I-Beams. I never cared enough to ask but knew better than to try and correct them because that's pretty annoying heh.
It's good you didn't correct them because they aren't the same thing. Wide flange beams have wider flanges that don't taper or taper less than I beams. Your architecture friends were probably using the right lingo.
When I started here, all there was was swamp. All the kings said I was daft to build a castle on a swamp, but I built it all the same, just to show 'em. It sank into the swamp. So I built a second one. That sank into the swamp. So I built a third one. That burned down, fell over, then sank into the swamp. But the fourth one stayed up. And that's what you're going to get, Lad, the strongest castle in these islands.
The real world version of that: The causeway for the Lucin Cutoff across the Great Salt Lake.[1]
The Southern Pacific dumped in fill rock starting in 1902, and the rock sank into the sediment. But they didn't give up. They kept dumping in more rock. They still couldn't get above the water line. So they built wooden trestles on the foundation thus created.
That worked, but the trestle was too weak and limited to slow trains. So eventually, the Union Pacific dumped in far more rock and built a solid rock causeway all the way across the lake. The causeway had to be raised in 1986 and strengthened.
Today, it carries long UP freight trains, part of the transcontinental main line.
The Otira Gorge Viaduct in New Zealand, that carries a highway that crosses the Southern Alps, has its foundations in a deep layer of talus that has fallen off Hills Peak over centuries - that movement of rock being why they built the viaduct to replace the road - as the slope eroded the road had to be moved higher up the slope, adding more switchbacks to the infamous Zig Zag [0]. Plus the falling rock that made the road dangerous.
They were determined to hit bedrock, but yeah, was buried too deep. [1]
The fascinating thing about the Munich gravel plain is that it's really just a (very slightly inclined) plain - it's almost 100% flat, and the gravel is covered by a (relatively thin) layer of soil, so you could easily mistake it for the typical "lowlands" alluvial plain, and you'll probably be surprised to learn that it's at a height of ~400-700 m. So you don't really have to worry about the gravel moving - but it's still there...
There are three floating bridges on Lake Washington in the Seattle area as well. The Lacey V. Murrow Memorial Bridge[0], the Homer M. Hadley Memorial Bridge,[1] and the world's longest floating bridge the Evergreen Point Floating Bridge.[2]
(note -- was a bridge engineer in Seattle and did work on the old 520 bridge when we designed the retrofitted post-tensioning it in the late 90's. Among other tasks, I supervised a guy drilling holes in the bottom of the bridge with a concrete corer. )
IMO it's probably a better idea to just keep on collecting them, and putting it away for the future. E.g. the I-5 bridge(s) across the Columbia River had tolls which stopped when Oregon & Washington bought the bridge, and now look where we are at. We have a 110 year old bridge needing replacement and no funds set aside for it. So what they will undoubtedly do is add tolls after spending a few billion to build a new bridge, and eventually it will get paid off. We could have been saving up for the cost and getting interest on it instead of the other way around. Even with a fairly modest toll, when you have a century to save.
This does require some legislative fortitude, however, to set aside the money for real and not just spend it on other things.
We did that here in Seattle, where we have the longest floating bridge in the world, SR 520 across Lake Washington: tolls stopped in 1979 after construction was paid off.
Alas, tolling resumed in 2011, to pay for the complete reconstruction of the bridge. This time we are probably stuck with it, since WSDOT has grown inordinately fond of tolling as a traffic-management tool.
> Plans for a bridge had existed since the 1960s, and after the decision to construct the bridge was passed by the Parliament of Norway in 1989, construction started in 1991. The bridge opened on 22 September 1994
Pretty impressive timeline for an innovative idea.
Ken Burns' documentary [0] about the construction of the Brooklyn Bridge was really fascinating discussing the innovative (at the time, late 19th century) engineering methods and challenges. It's pretty short, only 1 hour. Highly recommended.
The Japanese Pile driving company, Giken, has some great engineering videos of their silent pile driving technology and some novel use cases, such as stopping a lava flow, or making underground bike storage in cities: https://www.youtube.com/@GikenGroup/videos
Readit News
> The tagline of the Pile Driving Contractors Association is “A Driven Pile is a Tested Pile” because, just by installing them, you’ve verified that they can withstand a certain amount of force. After all, you had to overcome that force to get them in the ground. And if you’re not seeing enough resistance, in most cases, you can just keep driving downward until you do!
Deleted Comment
I feel that the cases in which that technique doesn't work are stories to be told. Do you just keep driving downward for a very long time? How long?
https://en.wikipedia.org/wiki/Staufen_im_Breisgau#Geothermal...
From a structural PoV, an extremely long piling in soft-ish soil will start having problems with lateral deflection - which it is too thin (relative to length) to resist. Then there's the case of "we think we finally hit bedrock...but what if it's just a big boulder?".
I can imagine cases of pilings running into large underground caverns, or penetrating strata containing water / gas / petroleum under pressure.
Edit: From a quick search...
In some locations, bedrock may not start until >1000' below the surface.
And here's a very quick & simple intro to the fact that "bedrock starts at depth D" is usually too simplistic: https://education.nationalgeographic.org/resource/bedrock/
> What the heck?
This is because the shapes are different. I beams are typically more slender through the web because the goal is to concentrate mass at the flange for moment capacity because they’re beams and geared towards bending. H piles are thicker in the web with the web thickness usually similar to the flange because the use case requires axial capacity and various constructability considerations. I beams turned into W (wide flange) and S sections in the standard shapes and H beams are called HP sections.
You’ll often see them cross-specified for foundation work but it’s rare that you’d choose an HP section over a more efficient section like a W or S for something “out of the ground.”
Useful graphic: https://en.wikipedia.org/wiki/File:I-BeamCrossSection.svg
I believe this is the same fundamental engineering method used in a swamp by Herbert's father in Monty Python and the Holy Grail. [0]
[0] https://m.youtube.com/watch?v=w82CqjaDKmA
The Southern Pacific dumped in fill rock starting in 1902, and the rock sank into the sediment. But they didn't give up. They kept dumping in more rock. They still couldn't get above the water line. So they built wooden trestles on the foundation thus created. That worked, but the trestle was too weak and limited to slow trains. So eventually, the Union Pacific dumped in far more rock and built a solid rock causeway all the way across the lake. The causeway had to be raised in 1986 and strengthened.
Today, it carries long UP freight trains, part of the transcontinental main line.
[1] https://utahrails.net/pdf/UP_Great-Salt-Lake-Causeway_2007.p...
What, the curtains?
There is always bedrock, but in some places your pile would have to be really long to reach it:
> The gravel deposits of 100 m (330 ft) are the deepest in the south of Munich and decrease towards the north.
(from https://en.wikipedia.org/wiki/Munich_gravel_plain - not saying this is anything really extraordinary, but it's the area I'm most familiar with)
They were determined to hit bedrock, but yeah, was buried too deep. [1]
[0]: https://teara.govt.nz/files/p-8788-gns.jpg
[1]: https://www.stuff.co.nz/national/117150792/awardwinning-otir...
https://en.wikipedia.org/wiki/Nordhordland_Bridge
[0] https://en.wikipedia.org/wiki/Lacey_V._Murrow_Memorial_Bridg...
[1] https://en.wikipedia.org/wiki/Homer_M._Hadley_Memorial_Bridg...
[2] https://en.wikipedia.org/wiki/Evergreen_Point_Floating_Bridg...
(note -- was a bridge engineer in Seattle and did work on the old 520 bridge when we designed the retrofitted post-tensioning it in the late 90's. Among other tasks, I supervised a guy drilling holes in the bottom of the bridge with a concrete corer. )
Let that sink in. They paid for the project and then stopped taking everybody’s money.
That was the plan in Chicago, too...
This does require some legislative fortitude, however, to set aside the money for real and not just spend it on other things.
Alas, tolling resumed in 2011, to pay for the complete reconstruction of the bridge. This time we are probably stuck with it, since WSDOT has grown inordinately fond of tolling as a traffic-management tool.
Man in Year 50: We need funding for much needed maintenance that has been neglected through sheer incompetence
:-\
Pretty impressive timeline for an innovative idea.
See: https://www.youtube.com/watch?v=gm0YQ3vuyyY
They are virtually unsinkable!
]0] https://kenburns.com/films/brooklyn-bridge/
The Great Bridge: The Epic Story of the Building of the Brooklyn Bridge by David McCullough
https://www.amazon.com/Great-Bridge-Story-Building-Brooklyn/...