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Why Bridges Don't Sink

bell-cot
35 replies
1d8h

Favorite bit:

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!
etrautmann
11 replies
1d3h

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.

kurthr
8 replies
1d3h

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.

leeter
7 replies
1d3h

It depends. Fully soaked ground will actually preserve wooden piles (wood decay is aerobic and requires oxygen). This is why Venice and New Orleans are both built on them (sinking issues aside because they have other issues). The piles in both cases are quite stable because the ground is completely soaked. Where you run into issues is where water and air meet. I would imagine wooden piles in just water would have issues with shipworm (in appropriate venues). But the ones in fully soaked soil seem to last just fine.

I suspect, but don't have data on, that wooden piles may actually last longer in those exact circumstances due to galvanic issues with concrete and rebar or metal pilings.

throw0101c
3 replies
1d2h

Fully soaked ground will actually preserve wooden piles (wood decay is aerobic and requires oxygen).

When building fences, the ground-air interface is often where rot occurs, and there are products to protect that area:

* https://www.postsaver.com/en-gb/products/pro-sleeve-fence-po...

bonestamp2
2 replies
1d

Any idea how well those stand up to lawn trimmers?

gknoy
1 replies
22h42m

It looks like a layer of plastics, so I would expect not well. Though, the part you'd hit would be above the ground, so it might still protect pretty decently for all the below ground stuff. You might consider putting a small set of stones around it so that the trimmer cord hits those instead of the wrapped wood.

throw0101c
0 replies
6h17m

You might consider putting a small set of stones around it so that the trimmer cord hits those instead of the wrapped wood.

Stones could help with drainage and drying as well.

eep_social
1 replies
1d2h

Venice and New Orleans are both built on them

Parts of Amsterdam as well.

Cthulhu_
0 replies
23h41m

But they don't last forever, so a lot of them are being replaced at the moment. Expensive operation as they have to be replaced in-place, but Amsterdam canal front houses are prime real estate.

Arrath
0 replies
21h38m

Not to mention that wooden piles were often treated with an absolutely massive amount of creosote, to the point that a number of timber pile treatment yards are superfund sites.

matt-attack
0 replies
4h25m

“the slow blade penetrates the shield“

gosub100
0 replies
1d

Especially for trains. For one, they are much more susceptible to sinking, but also likely produce all kinds of resonance.

SideburnsOfDoom
11 replies
1d7h

in most cases, you can just keep driving downward until you do!

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?

pas
0 replies
22h17m

Days after the disaster, once the water pressure equalized, nine of the eleven sunken barges popped out of the whirlpool and refloated on the lake's surface.

wow.

there were no human deaths, three dogs were reported killed. All 55 employees in the mine at the time of the accident escaped

omF...g the mine was active!? and folks were just drilling on top of it!???

huh. good old 1980s.

pixl97
0 replies
1d4h

Another one to watch out for is mud diapirs. In coastal deltas where thousands of feet of infill has occurred over time the interaction between hydrocarbon formation and organic silts can create mud volcanoes.

https://www.researchgate.net/figure/Comparison-of-signatures...

These can be anywhere things that shoot liquid mud out of the ground to areas of very deep low seismic velocities where you could drive a pile thousands of feet to the bottom of hell and barely get any resistance.

Much the same, one should be careful when drilling into mud layers

https://en.wikipedia.org/wiki/Sidoarjo_mud_flow

orls
0 replies
1d4h

This is fascinating, thankyou!

crazygringo
0 replies
1d4h

Wow. I knew drilling could cause land to sink. I never imagined it could cause land to rise.

Fascinating, thanks!

bell-cot
2 replies
1d6h

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.

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/

beerandt
0 replies
23h5m

Then there's the case of "we think we finally hit bedrock...but what if it's just a big boulder?"

Doesn't matter.

There's two types of pile support: noncohesive and cohesive. Which can be thought of as end (bearing) resistance and side (friction) resistance.

Most people only think of end resistance.

Most end resistance piles aren't driven to bedrock or even a boulder, but a strata of soil with sufficient strength. Usually a layer of sand under silt or clay, but a boulder could do it.

Here's the catch- if it's a one-off, then adjacent piles won't hit it, and you'll see the anomaly. Mitigation may or may not be required. If it's not, then you've hit a strong (noncohesive) layer of boulders.

Either way- it goes back to the point: each pile is resistance tested. And you know now not only the insitu soil strength, but also that of each layer to reach that depth.

Also side note- the act of driving and then post-drive settling both build addl strength. Eg, The force used to drive the pile, applied a few months later, usually won't be sufficient to drive it any further.

adolph
0 replies
1d5h

I can imagine cases of pilings running into large underground caverns

Example being the Lake Peigneur disaster.

https://64parishes.org/entry/lake-peigneur-drilling-accident

On the morning of November 20, 1980, the crew drilling near the salt mining operations reported that the tip of their drill shaft was stuck. After the crew removed the tip, they heard strange noises and abandoned the platform in the nick of time. A giant mud crater began sucking down barges, rigs, and almost some fishermen who escaped with moments to spare.

0xTJ
0 replies
1d7h

Satan, far below some very deep, soft, and slippery soil where an overpass needs to go:

What the heck?
steveBK123
8 replies
1d7h

Many have said similar about their code

CyberDildonics
6 replies
1d4h

What does this mean exactly?

steveBK123
1 replies
1d4h

works on my box

CyberDildonics
0 replies
1d3h

"if you’re not seeing enough resistance, in most cases, you can just keep driving downward until you do" -> "Many have said similar about their code" -> "works on my box"

How does this make sense or have any coherency?

marcosdumay
1 replies
1d3h

User-side tests are the only tests that really matter.

Everything else you do is there just to reduce the odds of users tests catching anything. But you don't get any certainty before that step... that happens after your software is on production and people depend on it.

(Of course, that's a worldview that can be either very beneficial or incredibly harmful depending on what you are creating. It's not good to see it applied to bridges, but I believe the OP did it in jest.)

gonzo41
0 replies
1d3h

That's why we call it big test, not production.

samtho
0 replies
1d4h

Utilizing “Brute Force” as a testing and verification strategy.

mardifoufs
0 replies
1d4h

Maybe it's a parallel to "if it runs, it works" :)

duped
0 replies
1d2h

Unless you are talking about fancy dependent typing you might misunderstand the quip. Writing code does not test it.

yencabulator
0 replies
1d1h

Tested at the moment of installation != test valid 30 years later

Log_out_
0 replies
1d1h

how does that hold up to quake liquification?

jtbayly
20 replies
1d3h

"The last tolls were collected on 31 December 2005.”

Let that sink in. They paid for the project and then stopped taking everybody’s money.

That was the plan in Chicago, too...

rootusrootus
14 replies
1d2h

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.

jppittma
6 replies
1d1h

To me, the way they've done it seems correct. In your mind, where does the interest come from on the money saved for the bridge? The government has to be collecting interest from somebody no?

rootusrootus
4 replies
1d

I assume the state can buy shares in index funds like the rest of us.

jppittma
3 replies
23h56m

So, lets expand that idea a bit. Why doesn't the government just buy a lot of shares in index funds, kind of like an endowment, and then never collect any taxes? I can see a world where a large portion of private enterprise is held/managed by the government, and the proceeds of that is used to fund public works.

rootusrootus
1 replies
22h49m

Well, the first reason is that most state governments[0] do not have anywhere near enough money in their accounts to get a return that will replace the revenue stream they get today through taxes. You might be able to build it over time by reinvesting budget surpluses.

The other problem I foresee is that the market is fickle. The S&P 500 reached a level in the second half of 2000 that it would not see again for over 14 years[1]. Any investment that needs to generate consistent revenue isn't going to have nearly the growth rate over the long haul that an index fund would provide. That makes the initial investment requirement significantly larger.

But otherwise, I am okay with the government owning a lot of private enterprise via index funds, so long as it has exactly the same voting power that I have. Which is to say, none.

[0] In case anyone needed the clarification, this whole discussion is about state governments; it does not really apply to the federal government for obvious reasons.

[1] Adjusted for inflation. The index did recover to the same number in 2007 just before dropping 50% in 2008.

jppittma
0 replies
6h38m

Well, for the sake of argument, let’s say the federal government prints all of the money the state would need for an endowment and hands it to the state. There is inflation, but the state never has to collect taxes again.

I think there are some small optimizations we can make to this flow though, like what if the feds who printed the money held the endowment for the state and just distributed payments, instead of letting each state manage its own endowment.

Pretty much the same? Inflation, but no taxes.

wdh505
0 replies
19h33m

There is a principle of governance that "you are taxing too much" is soo easy to build a platform off of that you will be DOA in elections if you manage any government that tries to invest like you say.

Investment restricted to "government responsibility foresight" infrastructure gets enough flac already. It only takes one down turn for the "golden goose" of the investment to be spent on the buddies of who just got into office

kortilla
0 replies
1d

Local governments use banks. What are you getting at?

pavon
4 replies
23h19m

On the other hand it is more fair for the people using the new bridge to pay for it than for previous generations to pay for the old bridge and then keep paying for the new one which they will never see.

rootusrootus
3 replies
23h1m

I consider infrastructure like bridges to be fundamental constructs of society, something we should build to promote the general welfare. I willingly pay for infrastructure today that will get more use by my children than I will ever see, and I think that is fair. My parents contributed to much of the infrastructure I am using.

pavon
1 replies
19h28m

There is a huge difference in being taxed to create and maintain infrastructure that you and your children will both use, and being taxed to fund future hypothetical infrastructure that you will never use.

I don't like that we as a country put off the costs of maintenance as long as possible thus creating debt for future generations, but asking the current generation to create a savings fund to pay the future generation's (non emergency) expenses is a bridge too far.

sethammons
0 replies
4h58m

"A society grows great when old men plant trees whose shade they know they shall never sit in"

rty32
0 replies
20h42m

willingly pay for infrastructure today that will get more use by my children than I will ever see

Well, not many voters think that way...

gosub100
1 replies
1d

You can't trust politicians to just save money for the future. It will be abused by both sides. One side will gain votes by diverting it to something that has nothing to do with transportation, the other side will gain votes by repealing it and taking credit for lowering taxes.

rootusrootus
0 replies
22h39m

I agree, it would be tough to implement, and I do not have an easy answer. Maybe something like a deposit-only account with a binding agreement on the earliest date the money can be withdrawn. No, I do not know how such a thing could be created in practice :). If it were possible, that would address the first issue, but not the second.

renewiltord
0 replies
1d1h

Man in Year 10: See, this is how you do it. No tolls.

Man in Year 50: We need funding for much needed maintenance that has been neglected through sheer incompetence

marssaxman
0 replies
1d1h

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.

duped
0 replies
1d2h

Still is the plan, they just keep building and rebuilding the roads.

amclennon
0 replies
1d2h

Tolls were reinstated on the bridge in 2019 to finance other road projects in the area

:-\

BobaFloutist
0 replies
22h0m

How do they pay for maintenance?

knute
2 replies
1d5h

I'm not an expert but I have seen Titanic (1997) and I would think a floating bridge is most vulnerable to sinking.

RajT88
1 replies
1d

Nah. You see the floating bridge is compartmentalized, so that it is impossible for an entire segment to flood at once and sink.

They are virtually unsinkable!

cyberax
0 replies
21h58m

Seattle: hold my beer.

wiredfool
0 replies
1d5h

And one on the bottom, no longer floating.

(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. )

tamimio
1 replies
1d3h

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.

IncreasePosts
0 replies
1d2h

And here in NY we've had 4 generations working on the 2nd ave subway line and only 3 of planned 15 stations have been opened so far.

rob74
8 replies
1d8h

Quote-unquote “bedrock” is a simple idea, but in practice, geology is more complicated than that.

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)

EdwardDiego
7 replies
1d8h

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]

[0]: https://teara.govt.nz/files/p-8788-gns.jpg

[1]: https://www.stuff.co.nz/national/117150792/awardwinning-otir...

quibono
5 replies
1d5h

TIL New Zealand have their own Alps!

stonemetal12
2 replies
1d4h

Technically "Alps" is the plural of "alp", which means a very high mountain.

wongarsu
1 replies
1d2h

However "alp" comes from Latin "Alpes", which is the mountain range in Western Europe we now call the Alps.

The word has become genericized to a degree. One the other hand Alps used to be one very specific mountain range, and alp a mountain in that mountain range, so surprise at some other place calling their mountain range Alps is understandable.

fsckboy
0 replies
1d

surprise at some other place calling their mountain range Alps is understandable

yes, if you come from Wellington in Suffolk and you fly to Wellington in NZ, and then encounter that the nearby mountains are called Alps, you would be shocked, shocked

munificent
0 replies
1d

The North Cascade Mountains in the Pacific Northwest are also sometimes called the "American Alps".

(Personally, I think it's a silly name. The Cascades are majestic enough in their own right and need no comparison to any other mountains.)

rob74
0 replies
10h48m

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...

cyberge99
7 replies
1d5h

I have a guess to why H Pile i stead of I Pile: pronunciation. The initial I seems almost silent when saying I Pile. Whereas with H there’s a more distinct sound.

dpcx
6 replies
1d5h

Isn't that the same with I-Beam as well?

me_me_me
5 replies
1d3h

I-Beam rolls of the tongue H-Beam doesnt, I guess thats the reason for adopting I term over H term

gosub100
2 replies
1d

My pet peeve along this line is O-ring. Is there any other conceivable shape for a ring?

gosub100
0 replies
4h22m

good call, thank you

dpcx
1 replies
1d3h

The context was the silent-ness of I vs H, not what rolls off the tongue. I agree that I Pyle rolls better, though.

zardo
0 replies
1d

Too close to Apple's trademarked iPile

quaintdev
3 replies
1d

Shame that website does not have RSS

jimbobthrowawy
1 replies
23h27m

I think all of the blogposts are just transcripts of videos from his youtube channel. You could use the feed from youtube to tell when there's a new release.

Wait, I just checked the page source after writing the above to confirm and it looks like it does have one: https://practical.engineering/blog?format=rss

quaintdev
0 replies
15h23m

Thanks. Miniflux could not find it. I did not know that this can happen.

Even authors are probably not aware of this.

chmaynard
0 replies
0m

[delayed]

Terr_
3 replies
1d10h

But, what if you just keep loading it and causing it to sink deeper and deeper?

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

bityard
1 replies
1d5h

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.

Animats
0 replies
23h48m

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.

[1] https://utahrails.net/pdf/UP_Great-Salt-Lake-Causeway_2007.p...

jonplackett
0 replies
1d9h

One day son, this will be all yours!

What, the curtains?

abduhl
2 replies
1d6h

> 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.”

chasd00
0 replies
1d5h

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.

VWWHFSfQ
2 replies
1d5h

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.

]0] https://kenburns.com/films/brooklyn-bridge/

VWWHFSfQ
0 replies
1d

Oh yes McCullough narrated the Burns doc. Brilliant historian

mdrzn
1 replies
1d4h

TIL that "Piledriver" wasn't invented by WWE.

samf
0 replies
1d3h

The WWE didn't invent it, they perfected it.

lacoolj
1 replies
1d1h

this was such a great way to spend 17 minutes thank you for posting! I feel like I learned so much about foundations that I never would have otherwise on my own lol

bloaf
0 replies
20h49m

This guy’s videos are consistently great, they get a lot more technical than most other edutainment without getting bogged down.

relwin
0 replies
1d2h

The bridge in the thumbnail is the Coronado bridge, rumored to have a floating hollow-box mid-section so that in the event of a collapse Navy ships can easily push debris and clear a channel. I remember hearing this "fact" on a San Diego harbor cruise long ago. Alas Wikipedia says it's a myth...

nanomonkey
0 replies
3h24m

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

KolmogorovComp
0 replies
1d3h

Tangential but does someone know the animation software used to display extract of the FHWA report, starting from 1:45? It seems to be used a lot by journalists and looks fantastic.