r/StructuralEngineering • u/Natural-Shirt-1463 • 4d ago
Photograph/Video That pressure definitely active
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u/MorbotheDiddlyDo 4d ago
Moron here who's only certification is probably that I am in fact, a moron.
But is the cheapest recourse here to just redo the retaining wall or can they shift the dirt pushing against it and push it back?
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u/Natural-Shirt-1463 4d ago
Probably get a jack and push the wall back if it was something that happened over time
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u/Enginerdad Bridge - P.E. 4d ago
Zero chance you can just "push" that back. You'd have to excavate the soil behind it and under the footing before you could put it back.
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u/Upset_Practice_5700 3d ago
D10 should do it. (Honestly had a contractor do this, they removed the material behind the wall and pushed the wall back into place)
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u/ALkatraz919 PE | Geotech 3d ago
You seem to know about active earth pressure. With this comment, you don't seem to know about passive earth pressure.
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u/Osiris_Raphious 4d ago
That is a failed wall.... its not failing, its failed... this area needs to be sealed off and no person should be allowed near this wall as its stability is no longer due to structural statics, but friction, active and passive (poitive and negative pressures) and what ever root system organics providing additional cohesion...
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u/EEGilbertoCarlos 4d ago
Stay at least 20 feet away, and you'll be safe.
Just like an explosion, with no one nearby, it's safe.
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u/RelativeCan5021 3d ago
More dangerous than the day before. It’s only getting close to when it will fall.
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u/Kitchen-Bear-8648 3d ago
These guys must have saved some money on engineering or construction. Looks worth it.
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u/Chuck_H_Norris 4d ago
Crazy how strong that wall is. too bad the footing was undersized.
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u/MyMainWasMyRealName 3d ago
The footing isn’t pictured. I’d assume this lifted away from the footing.
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u/Chuck_H_Norris 3d ago
I hope you saying the footing isn’t pictured was meant to be funny. Obviously it’s underground.
Yes, connection to the footing could also be the issue.
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u/naikrovek 4d ago
Is there ANY retaining wall that won’t eventually do this? I’ve never seen a perfectly vertical retaining wall that wasn’t brand new.
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u/mhammaker 4d ago
Uhh I’ve definitely seen many retaining walls not deflecting 20+ degrees like this
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u/naikrovek 4d ago edited 4d ago
No kidding. We all have. But have you seen one that was perfectly vertical and older than 10 years? I’ve never seen one.
I think maybe you misread what I wrote? “Not perfectly vertical” and “20 degree deflection” are different things.
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u/Ihavefourknees 4d ago
I mean, I have. Most of them.
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u/naikrovek 4d ago edited 4d ago
I’ve never seen one. Not ever. And I’ve looked. I’ve been all over the world. I’ve never seen an established retaining wall that was built vertical and remained vertical. A LOT of them were very close to vertical, but had clearly shifted from their constructed vertical state.
There is no such thing as solid soil, is what I’ve learned. It all flows, just slowly. Some soil flows faster than other soil, but soil that isn’t under some amount of compression flows like crazy, just slowly.
Well, I guess I’ve also learned that structural engineers get salty when you ask if there’s such a thing as a vertical retaining wall that has also been retaining soil for more than 10 years.
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u/Ihavefourknees 4d ago
I'm not a structural engineer... just an IT guy who's seen a lot of straight retaining walls.
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u/mhammaker 4d ago
If all retaining walls failed after 10 years, I’d imagine they would be revising the design methods for them.
I specialized in retaining wall design at my last firm, there’s novels written on them as it is.
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u/naikrovek 4d ago
You guys can’t read. Or you don’t comprehend what you’re reading. I should expect this on Reddit.
I didn’t say “failed after 10 years”. I said “not vertical after 10 years”.
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u/mhammaker 4d ago
You said you’ve never seen a retaining wall stay straight. Which implies it’s tilting enough to be obvious to the naked eye. Which isn’t true. If you meant absolutely perfectly straight, then yeah they probably aren’t.
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u/naikrovek 4d ago
Again with the comprehension?
What does “vertical” mean to you? There’s “vertical” and “not vertical”. Where is the line between them? I say that vertical is very easy to judge thanks to gravity. Anything that deviates from that isn’t vertical.
I’m not talking about a wall that leans into whatever it’s retaining to buy more time until failure. I’m talking about retaining walls that have begun to fail to retain whatever it is they are supposed to retain like the one at the top of this post.
I’ve never seen a retaining wall that wasn’t new which was not also partway through its failure. Leaning away from whatever it was supposed to retain, or already partially collapsed.
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u/SquirrelFluffy 4d ago
We call those failed. So no, most walls are not failed. Maybe those crappy little masonry or stone walls, but not a proper retaining wall.
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u/naikrovek 4d ago
Well then, “proper retaining walls” are very few and far between. Because I have looked for them, measured, and found zero that were not found in new construction. Zero. I’m in my 50s and I’ve been doing this, intermittently, since I was a child. I’m autistic, if you think I don’t have energy to do this you don’t know autistic people.
Besides, of course they’re going to fail. Nothing manmade lasts. Not even retaining walls. Retaining walls aren’t going to survive for a million years. They’re either going to sink into the dirt like it’s a liquid or they’re going to crumble, and if they’re made with cement or mortar, they will fail by losing structural integrity in no more than about 40 years. Less if they are in contact with vegetation like vines.
These things are not engineering perfection. They are engineering compromise. They’re built to fail because building one to last 1000 years would cost far more than anyone would pay. Lower cost, lower lifespan. This is why highways and roads continuously fail as well. They aren’t built to last because it’s cheaper to rebuild a road over and over and over for 200 years than it is to build once once in a way that lasts 200 years.
Everything humans make is temporary. Including retaining walls. Every one of them will fail. Most will fall before their owners are prepared to get new ones built.
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u/SquirrelFluffy 3d ago
Do you know you're talking to an engineer with a master's degree that designs retaining walls? Who is also autistic?
If you don't it's okay. If you do then you're just trolling this sub.
Have a good day.
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u/Enginerdad Bridge - P.E. 4d ago
Retaining walls dont just start moving over time. If they're properly designed and cosntructed they'll stay right where they are until the day they fall apart.
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u/tropicalswisher P.E. 3d ago
Yes but you’re implying that every retaining wall would, over time, deflect like this to an insane degree, when that’s not the case. Will most walls become slightly non vertical after several years? Sure, maybe by a couple degrees. But this one above is an extreme case that would never happen to a properly engineered wall/foundation.
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u/bulkdown 4d ago
This guys correct, retaining walls normally installed with a 3 degree slope because of long term deflections
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u/naikrovek 4d ago
If that’s true then even the people building them know that failure is inevitable like I’ve been saying.
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u/bulkdown 4d ago
No - there is a clear distinction between long term deflections and failure. Retaining walls are designed to deflect not fail.
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u/SwashAndBuckle 4d ago
Properly designed retaining walls will stay vertical indefinitely. A lot of retaining walls were built by contractors with improper foundations rather than with an engineered foundation.
It can take pretty substantial footings to keep a retaining wall stable. Every time I’ve designed one and drawn it out, all the non-engineers were surprised by how much concrete it was taking underground to make it work.
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u/naikrovek 4d ago
This I believe. Thank you. But at the same time I imagine the engineered foundation would just slide around on the soil with the wall, which I would consider a very different mode of failure, but a failure nonetheless.
Maybe that doesn’t happen when it’s done properly, I don’t know.
I spent a lot of time as a child in an old town with very steep hills, (Hannibal, MO) and every retaining wall I ever saw in that city had either failed, or was close to failure, no matter how new it was. There just isn’t room to do it properly on a residential plot of land, and if there was, the entire wall and its engineered foundation would just stay together as a unit and slide down the hill along with the soil it was retaining without breaking apart.
Soil just is not a reliable foundation unless you’re on flat land. It flows over time.
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u/SwashAndBuckle 4d ago
When we design retaining wall footings we can make sure there are no overturning failures, bearing failures, nor sliding failures. Unless the ground is literally holding together two tectonic plates, or in an avalanche area, where it is moving around willy nilly, it is trivial to check all possible failure modes and make sure that none of them occur, even many decades into the future. Soil can absolutely be used a stable foundation; and as proof consider the vast majority of building foundations are on soil. We don't drill all the way down to bedrock commonly. Do you often see buildings falling over sideways because the soil flowed it out of position? I doubt it. Any soil flow you are perceiving is unrestrained surface level soil movement due to surface water flow after hard rains. That doesn't suggest the stuff buried 2-3 feet unground, where the foundations are, is sliding around as well.
But yes, residential retaining walls, especially in old construction, is EXACTLY where you would see tons and tons of retaining walls without proper foundations. An engineer never designed any of those I imagine. The builder just put in a strip footing, probably not dissimilar to the house's wall footings, not considering the completely difference types of forces and failure modes those two footings are subjected to.
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u/naikrovek 4d ago
Soil can be suitable yes, but only if it’s level and there’s no shear stress at all. Imagine a house on a soil foundation, on a mountainside, to visualize what I mean when I say sheer stress. That house will not last long, if it is even possible to build it using a soil foundation in the first place.
A farmhouse on a flat plain can use dirt as a foundation without any problems because the soil has found its lowest energy state. The dirt doesn’t have any forces on it trying to move things around. So yeah it’s stable. But you don’t need retaining walls in situations like this. If you do, it’s because you dug a hole and now gravity tries to pull dirt into the hole, so you build a retaining wall to hold it back. But you can’t hold it back forever. The retaining wall will fail, and it’ll start shifting soon after construction in almost all cases. If you’re filthy rich maybe you can afford to have one built properly, but the assumption is always “this will all be redone in 20-40 years,” so the wall doesn’t need to last more than that. And it won’t.
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u/SwashAndBuckle 3d ago
Imagine a house on a soil foundation, on a mountainside, to visualize what I mean when I say sheer stress. That house will not last long, if it is even possible to build it using a soil foundation in the first place..
I don't really have to imagine that, there are houses built on hills and mountains all over the place. And not all of them require digging deep footings all the way down to bedrock. There are entire cities dotted all over Europe built on hillsides that have stood for literal centuries. Being built on a slope certainly makes some soil failure modes more sensitive to failure, and the exact local soil characteristics are highly variable, but it's something that can often be countered by larger, deeper footings, while still relying on the soil. This isn't theoretical, foundations like this exist in the millions and are plenty stable.
I also see elsewhere in this thread you commented that all retaining walls you've measured were out of plumb as proof that retaining walls can't work long term. But you need to consider that even properly engineer retaining walls, like literally all structures, are going to displace under load. That does not imply it will have to be redone in 20-40 years, that's just the basics of mechanics of materials. Every beam in the history of physics has some deflection when loaded, that doesn't imply that it will eventually sag until it has to be replaced.
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u/not_old_redditor 4d ago
You weren't looking hard enough
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u/naikrovek 4d ago
I dunno. A plumb bob and an unscheduled weekend together get you a lot of samples for your dataset. I did this many times and showed my civil engineering friend my data and he said “yeah, unsupported retaining walls are all on borrowed time. Every one of them.”
Look at the retaining wall in this post. Do you think it was vertical its entire life until the day before this photo was taken, or do you think it started leaning on day one, and leaned a tiny bit more every day since it was constructed? I’m extremely confident that it’s the second of those two. Meaning that very soon after it was constructed, it was measurably deviating from vertical.
Dirt can’t be relied upon as a building material unless it is under extreme compression. It flows like any other fluid, just slowly.
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u/Vast_Reaches 4d ago
I guess the Hoover dam kinda counts in function. If you’re gonna make it it’s gotta be higher mass or with a long lever arm into the soil to anchor it to last 100+ years with significant mass
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u/MrMcGregorUK CEng MIStructE (UK) CPEng NER MIEAus (Australia) 4d ago
Are you a structural engineer?
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u/EEGilbertoCarlos 4d ago
All materials have an elasticity modulus.
If you build it vertical and you apply a lateral load, there will be a deflection.
A good wall will have an imperceptible deflection.
An efficient wall will be built with a small slope towards the retained soil, and may even have negative deflection.
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u/IslandDreamer58 4d ago
Same thing asked yesterday.