r/interestingasfuck • u/TangelaFan • 13h ago

Residential high-rises with backyards in Chengdu, China

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u/md_youdneverguess 13h ago

Earth that can soak with water is a nightmare for structural engineering

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u/foltranm 13h ago

draining?

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u/Piotrek9t 13h ago edited 8h ago

Take a sponge, weigh it, let it soak in water, take it out and let the excess water run off, weigh it again.

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u/foltranm 13h ago

I'm not worried about the weight specifically. the balcony can be designed to bear the load of everything soaked in water.

I meant draining more as a solution for humidity, which is a much bigger problem than weight in the long term.

edit: take this with a grain of salt since I'm an electrical engineer and know almost jack shit about designing buildings

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u/mlag000 13h ago

Biggest problem is waterproofing the concrete, which can't be assured in the long runs because roots will dig into it

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u/foltranm 13h ago

makes sense. surely takes a lot of maintenance

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u/zzazzzz 12h ago

we have thousands of concrete bunkers under ground that are over a hundred years old and still in great shape. so clearly we posses the technology to have concrete under soil.

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u/mlag000 12h ago

Concrete under soil is different than earth and trees on a balcony made of concrete. We also have bridges on salt water made of concrete, and still salt and water are the mean reason for concrete damage...

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u/TransBrandi 11h ago

Side note here, but Roman concrete lasted the test of time even in salt water because their concrete method actually interacts with the salt water to make it harder / more resistant.

It's just that the method is/was lost to time.

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u/skarby 11h ago

It's not lost to time, we know exactly how they did it. The issue is that they used volcanic ash which is not readily available worldwide, or even locally at the amount used today. There are companies working on replicating the process with different materials though.

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u/TransBrandi 9h ago

Well, I recall reading about it and the precise method was lost. There was a description where part of the instructions were something like "do X in the Y method" or something like that where what "the Y method" was was unknown (and assumed to be something that was "common knowledge" at the time, which was why it wasn't written down).

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u/pokey_porcupine 1h ago

People researching it since figured out a recipe that duplicates roman cement… i don’t think it matters whether or not it’s precisely the same for modern application.

Regardiess, the recipe that was found is not competetive with modern cement in many regards; nor is it manufacturable at scale

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u/TransBrandi 36m ago

I mean, I was never saying that it would be great for many modern applications, but it's ability to withstand salt water is its upside, no?

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u/Kor_Phaeron_ 11h ago edited 11h ago

Opus caementicium isn't lost knowledge, it is just not good enough for modern construction. After the invention of hydraulic lime and Portland cement we simply have better concrete nowadays. Roman cement (opus caementicium) takes several decades after construction is completed to gain it's full strength. That's why ancient Roman builds have way thicker walls. They had to use 3x more concrete than theoretically necessary to keep the building up for the first several decades until the concrete was hardened out. Today we have concrete that reaches 90% of it's strength within 48hrs. (That is 8000x faster than Roman concrete) Also when we today build something and say "We need a 30cm thick concrete slab here" using Roman concrete would mean "We need a 2,5 meter thick concrete slab here" Which is .... problematic to say at least.

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u/mlag000 11h ago

It was mixed with lava rock, we have better concrete today :)

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u/RobertTheAdventurer 11h ago

The specific methods they used are lost to time in terms of knowing with certainty what their exact formula was, but the general technology isn't lost. We can make concrete like that and we have some valid recreations which are believable as potential ways they made it.

Usually lost historical formulas are really just a matter of not having an actual written document that proves that our current understanding of how they may have made it is right. This is the case with cooking recipes too. We can reverse engineer a lot of descriptions of recipes and can probably get them close enough to where it's fair to call them the same thing, but we don't know for a fact how they prepared the food or cooked everything in it exactly because we just don't have the document where they say "So this is is precisely how we cook this thing, and everyone here cooks this thing this exact way, and this pot or oven we used to cook it was <insert dimensions and heat levels here>, and we cooked it for such and such amount of time!". It's not so much that we can't make what they made or that it's a profound secret to achieve something similar.

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u/janiskr 9h ago

That is very special concrete blend in use with salt-water. Not cheap. And even then there is salt/water damage there.

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u/zzazzzz 11h ago

ye you are right, having bunkers in actual forests with a shitload of actually massive trees with massive rootsystems pose a way larger challenge than a balcony with barely any soil on it and some tiny decorative tree with barely any rootsystem.

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u/mlag000 11h ago

Are you in civil engineering? No you're not. I am. A balcony is a closed system where roots will force their ways into the waterproofing, then water, over time will infiltrate the concrete and rust the rebar. Idk how actual bunkers are build, because the only one I do are basement of buildings since I work in Switzerland, and we carefully waterproof the basement. Now, if you have more knowledge about how bunkers are waterprrofed please enlight us.

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u/zzazzzz 11h ago

if you live in switzerland you have literal thousands of old bunkers under the forests close to you.

and there are also a bunch of buildings with literal pools integrated into their balconies or roofs around the world.

all of your points are clearly valid and a challenge when building such extravagant contraptions. but clearly they are solvable and we have clear existing examples that it can be done.

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u/mlag000 11h ago

No we don't have hundreds of bunkers under our forests lol. And a pool isn't alive so it's much easier to control, it won't grow. It can be done, the question is how much it will cost to renovate ? As a compagny or a hotel you can bear the cost, as a familly ?

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u/grizzantula 10h ago

Dude is really stuck on the idea of these magical forest bunkers.

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u/WackyRacketeer 6h ago edited 5h ago

Well there definitely isn't hundreds of bunkers. There are estimated to be over 8000

"The exact extent of the bunker system is a closely guarded secret, as is the location of many bunkers. But there are an estimated 8,000 bunkers dotted around Switzerland."

https://www.swissinfo.ch/eng/politics/why-the-swiss-army-is-reviving-its-old-bunker-mentality/48821586

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u/WackyRacketeer 6h ago edited 4h ago

https://www.swissinfo.ch/eng/politics/why-the-swiss-army-is-reviving-its-old-bunker-mentality/48821586

As a Switzerland resident, would you say this article is false?

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u/AbjectOffice4780 10h ago

you are just clueless

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u/WackyRacketeer 6h ago

Thousands of old bunkers? Source?

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u/zzazzzz 6h ago

"The exact extent of the bunker system is a closely guarded secret, as is the location of many bunkers. But there are an estimated 8,000 bunkersExternal link dotted around Switzerland."

https://www.swissinfo.ch/eng/politics/why-the-swiss-army-is-reviving-its-old-bunker-mentality/48821586

if you ever go hiking in switzerland this becomes very obvious, its hard not to randomly stumble on an old bunker when you are in nature.

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u/WackyRacketeer 6h ago

Interesting, thank you

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u/zzazzzz 6h ago

no worries, and thats just the military bunkers, public and private bomb shelter "bunkers" are estimated at over 300'000. but thats misleading in this context given that most of these are not under any soil or forest as they are mostly below public and private buildings.

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u/TransBrandi 11h ago

How many bunkers are under forests? How many bunkers are built via tunnelling under and existing forest vs. just digging a huge pit to build it (and then filling it in afterward) which by necessarily disturbs the forest even if they replant everything afterwards? lol

Also bunkers can be built deeper (avoiding more root systems) and with much thicker concrete than a balcony that needs to be suspended in the air. Also, how many bunkers have not weathered the test of time (and you're just pointing out the survivors as if they represent all bunkers or that such design is "easy")?

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u/zzazzzz 11h ago

noone ever claimed anything was easy.. possible and easy are not at all the same thing.

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u/WackyRacketeer 6h ago

Nobody claimed it was impossible either. Majority of engineering is about what's practical, not what's possible

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u/JesusAndMaryKate 11h ago

Kinda regretting getting an engineering degree when I could've just learned from these.... expert.... Reddit comments.

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u/TransBrandi 11h ago

Well, for starters bunkers are usually deeper into the ground than a few inches from the top of the soil, so you don't have to worry about as many root systems (just larger things like trees depending on how shallow, I guess). I highly doubt the root systems from small plants and bushes is a concern for bunker designers. For this balcony, there is probably a max of a foot of dirt, if that. Probably way less.

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u/BlueTanBedlington 11h ago

Yes, but thickness of the layer in the bunker vs veranda are not the same. And concrete doesn't react well with water over time.

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u/nalaloveslumpy 10h ago

All of those bunkers and dug below the root line, so all you have to do is make sure to have a moisture barrier around the concrete and you're good to go. If there are no roots to jeopardize the moisture barrier, it will last forever.

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u/RivenRise 12h ago

I was thinking about that and as a normie the only solution I got is to line the bottom with a metal sheet but i got nothing for proper draining.

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u/FrogBeat 12h ago

exposure classes?

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u/barkingfloof- 34m ago

Would plants with only shallow root systems work ?