[HN Gopher] Why Bridges Don't Sink
___________________________________________________________________
Why Bridges Don't Sink
Author : chmaynard
Score : 270 points
Date : 2024-07-02 23:43 UTC (23 hours ago)
(HTM) web link (practical.engineering)
(TXT) w3m dump (practical.engineering)
| Terr_ wrote:
| > 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
| jonplackett wrote:
| One day son, this will be all yours!
|
| What, the curtains?
| bityard wrote:
| 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 wrote:
| 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...
| srott wrote:
| Some of them wont sink because they float...
|
| https://en.wikipedia.org/wiki/Nordhordland_Bridge
| voxadam wrote:
| 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]
|
| [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...
| wiredfool wrote:
| 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. )
| knute wrote:
| I'm not an expert but I have seen Titanic (1997) and I would
| think a floating bridge is most vulnerable to sinking.
| RajT88 wrote:
| 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 wrote:
| Seattle: hold my beer.
| tamimio wrote:
| > 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 wrote:
| 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.
| jtbayly wrote:
| "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...
| amclennon wrote:
| > Tolls were reinstated on the bridge in 2019 to finance
| other road projects in the area
|
| :-\
| rootusrootus wrote:
| 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 wrote:
| 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?
| kortilla wrote:
| Local governments use banks. What are you getting at?
| rootusrootus wrote:
| I assume the state can buy shares in index funds like the
| rest of us.
| jppittma wrote:
| 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 wrote:
| 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.
| wdh505 wrote:
| 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
| gosub100 wrote:
| 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 wrote:
| 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.
| pavon wrote:
| 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 wrote:
| 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.
| rty32 wrote:
| > 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...
| duped wrote:
| Still is the plan, they just keep building and rebuilding the
| roads.
| renewiltord wrote:
| 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 wrote:
| 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.
| BobaFloutist wrote:
| How do they pay for maintenance?
| cyberax wrote:
| I live in Seattle. _Our_ bridges sink!
|
| See: https://www.youtube.com/watch?v=gm0YQ3vuyyY
| rob74 wrote:
| > _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 wrote:
| 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 wrote:
| TIL New Zealand have their own Alps!
| stonemetal12 wrote:
| Technically "Alps" is the plural of "alp", which means a
| very high mountain.
| wongarsu wrote:
| 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 wrote:
| > _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 wrote:
| 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.)
| pimlottc wrote:
| Australia, too: The Victorian Alps [0]
|
| 0: https://en.wikipedia.org/wiki/Victorian_Alps
| bell-cot wrote:
| 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!
| SideburnsOfDoom wrote:
| > 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?
| 0xTJ wrote:
| Satan, far below some very deep, soft, and slippery soil
| where an overpass needs to go:
|
| > What the heck?
| bell-cot wrote:
| 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/
| adolph wrote:
| > 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._
| beerandt wrote:
| >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.
| moffkalast wrote:
| https://en.wikipedia.org/wiki/Kola_Superdeep_Borehole
| lqet wrote:
| Well, whatever you do, do _not_ perforate an anhydrite layer!
|
| https://en.wikipedia.org/wiki/Staufen_im_Breisgau#Geothermal.
| ..
| orls wrote:
| This is fascinating, thankyou!
| pixl97 wrote:
| 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
| crazygringo wrote:
| Wow. I knew drilling could cause land to sink. I never
| imagined it could cause land to _rise_.
|
| Fascinating, thanks!
| Terr_ wrote:
| Also don't accidentally let a lake--and the boats in it--
| start filling your tunnels through salt.
|
| https://en.wikipedia.org/wiki/Lake_Peigneur
| pas wrote:
| > 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.
| steveBK123 wrote:
| Many have said similar about their code
| CyberDildonics wrote:
| What does this mean exactly?
| samtho wrote:
| Utilizing "Brute Force" as a testing and verification
| strategy.
| mardifoufs wrote:
| Maybe it's a parallel to "if it runs, it works" :)
| steveBK123 wrote:
| works on my box
| CyberDildonics wrote:
| _" 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 wrote:
| 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 wrote:
| That's why we call it big test, not production.
| duped wrote:
| Unless you are talking about fancy dependent typing you might
| misunderstand the quip. Writing code does not test it.
| etrautmann wrote:
| 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 wrote:
| 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 wrote:
| 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.
| eep_social wrote:
| > Venice and New Orleans are both built on them
|
| Parts of Amsterdam as well.
| Cthulhu_ wrote:
| 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.
| throw0101c wrote:
| > _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 wrote:
| Any idea how well those stand up to lawn trimmers?
| gknoy wrote:
| 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.
| Arrath wrote:
| 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.
| gosub100 wrote:
| Especially for trains. For one, they are much more
| susceptible to sinking, but also likely produce all kinds of
| resonance.
| Log_out_ wrote:
| how does that hold up to quake liquification?
| yencabulator wrote:
| Tested at the moment of installation != test valid 30 years
| later
| abduhl wrote:
| >> 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 wrote:
| 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.
| pimlottc wrote:
| Important bit of background knowledge: "The horizontal elements
| of the I are called flanges, and the vertical element is known
| as the "web"."
|
| Useful graphic:
| https://en.wikipedia.org/wiki/File:I-BeamCrossSection.svg
| VWWHFSfQ wrote:
| 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/
| HNDen21 wrote:
| Read this a few years back.. highly recommended
|
| 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/...
| VWWHFSfQ wrote:
| Oh yes McCullough narrated the Burns doc. Brilliant historian
| cyberge99 wrote:
| 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 wrote:
| Isn't that the same with I-Beam as well?
| me_me_me wrote:
| I-Beam rolls of the tongue H-Beam doesnt, I guess thats the
| reason for adopting I term over H term
| dpcx wrote:
| 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 wrote:
| Too close to Apple's trademarked iPile
| gosub100 wrote:
| My pet peeve along this line is O-ring. Is there any other
| conceivable shape for a ring?
| zardo wrote:
| Doesn't that refer to the cross-section?
| https://www.allorings.com/x-ring-seals
| mdrzn wrote:
| TIL that "Piledriver" wasn't invented by WWE.
| samf wrote:
| The WWE didn't invent it, they _perfected_ it.
| KolmogorovComp wrote:
| 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.
| relwin wrote:
| 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...
| surfingdino wrote:
| Some do sink, on purpose
| https://en.wikipedia.org/wiki/Submersible_bridge, and some are
| mis-designed
| https://en.wikipedia.org/wiki/Lacey_V._Murrow_Memorial_Bridg...
| lacoolj wrote:
| 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 wrote:
| This guy's videos are consistently great, they get a lot more
| technical than most other edutainment without getting bogged
| down.
| quaintdev wrote:
| Shame that website does not have RSS
| jimbobthrowawy wrote:
| 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
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(page generated 2024-07-03 23:01 UTC)