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Why Retaining Walls Collapse
- ggm 5y agoCalls out for pictures. Begging for some diagrams.
- mitchdoogle 5y agoDid you watch the video? That's the primary content. The article is basically just the script for the video
- ggm 5y agoI did not. Thanks, good call. [Edit] Then, later on I did. His graphics and cutaway models are really good.
- Raidion 5y agoI think this is a great article about something that I didn't understand. However, as feedback, what separates this from top tier articles is a lack of pictures and diagrams. Just adding a few of those to illustrate the different types of walls would make this content more engaging and link it to real world examples. I'm not likely to google "soil nail", but I'm def open to spending more time on your page to check out an example.
- loonster 5y agoI thought the article was in a weird place. It read like a very long introduction. If its the first in a series, its great. If its a standalone article, it lacks needed depth.
- frosted-flakes 5y agoAs others have said, this is the script for a YouTube video, not an article. The video is right at the top of the page.
- Cerium 5y agoThis is a transcript of a YouTube video. I'm sure there are diagrams and visuals in the video.
- loudmax 5y agoGrady's web site seems to be experiencing the HN hug of death right now, but I watched the video last night on Nebula, and there definitely are visuals and they definitely clarify the lecture. And as usual, Grady has built a practical demonstration of the forces and it also helps.
- mikestew 5y agoA good, explanatory article that could really use some diagrams, photos, or other illustrations. "Both mechanically stabilized earth and soil nails are commonly used on roadway projects, so it’s easy to spot them if you’re a regular driver." That sentence would have made a lovely caption to the photo of the "easy-to-spot" soil nail that the article didn't include.
- adewinter 5y agoIt's really a transcript for the accompanying YouTube video (channel of the same name as the blog)
- jasode 5y ago>article that could really use some diagrams, photos, or other illustrations. The image at the top of the article is a clickable url to the Youtube video which has the diagrams/illustrations/etc. The page submitted to HN is really a pre-written script that Grady reads to narrate the video. The intended content for integrating visuals is really the video and not the script.
- pcmaffey 5y agoIs the author's name really Grady Hillhouse? Surely that's a stage name?
- naikrovek 5y agoDon't make fun of people's names, man. People don't usually choose their own names. If you're going to make fun of someone, make fun of something they choose to do, instead of the things they don't choose. I'm confident it's his real name.
- pcmaffey 5y agoIs that making fun of his name? Or is it simply pointing out / wondering whether he a) chose a profession aligned with his given name, or b) chose a name aligned with his profession?
- handrous 5y agohttps://en.wikipedia.org/wiki/Nominative_determinism https://en.wikipedia.org/wiki/Nominative_determinism https://en.wikipedia.org/wiki/Aptronym https://en.wikipedia.org/wiki/Aptronym These things just happen.
- llefoll 5y agoYou've never heard of aptronyms?
- yjftsjthsd-h 5y agoLots of people have never heard of X for almost any value of X. Even if one had, it can be surprising to encounter an actual case of the thing in the wild.
- irrational 5y agoIt's like wondering about the English Professor named William Shakespeare. Would he have become an English Professor is named by any other name? https://www.ratemyprofessors.com/ShowRatings.jsp?tid=188354 https://www.ratemyprofessors.com/ShowRatings.jsp?tid=188354
- SECProto 5y agoIf you click the image at the top, it will load the youtube video[1] (which is the better source in my opinion - the blog is essentially closed captioning for the video, without any of the graphics). The only indicator is a small play triangle in the centre of the image/link - the cursor doesn't change on mouseover. [1] https://www.youtube.com/watch?v=--DKkzWVh-E https://www.youtube.com/watch?v=--DKkzWVh-E
- rob74 5y agoI realized something was fishy when I read "I’m Grady and this is Practical Engineering" at the end of the first paragraph... but still, I appreciate these articles, easier to skim through than a video. And if you're really interested, you can still watch the video...
- SECProto 5y agoThat's fair - I've just watched a lot of his videos (I think they're great), and the visual aids really make the explanations intuitive.
- kevincox 5y agoI agree. I already watched the video and was surprised that I couldn't find a link from this page. The fact that the header image is clickable is very non-intuitive. At the very least the cursor should change on hover.
- zymhan 5y agoAh thank you, I was quite annoyed that I couldn't grok a lot of the concepts without an accompanying picture
- Arainach 5y agoThis is a decent very high-level approach, but doesn't go into the practical applications for most people. If you're a civilian looking at small to moderate-sized retaining walls on your personal property (4 feet or less in height) rather than a civil engineer designing massive projects for infrastructure, your retaining walls are almost certainly failing due to issues with drainage (not enough drainage material, incorrect drainage material) or possibly a heavy surcharge rather than the forces described here.
- NikolaeVarius 5y agoDifference from an engineer. Anyone can make a thing, it takes an engineer to make a thing with minimal cost.
- jeffbee 5y agoWay I heard it as an undergrad in mechanical engineering is anyone can make a bridge that stands up but only an engineer can make a bridge that barely stands up.
- LegitShady 5y agofactor of safety on a typical bridge 2.5, so not really.
- adrianmonk 5y agoThen modify it to "only an engineer can make a bridge with a safety factor of barely 2.5".
- LegitShady 5y agoonly an engineer can tell you what your factor of safety is. Your other option is not knowing how sufficient what you built is at all.
- SeanFerree 5y agoInsightful article!!
- rob74 5y ago> Depending on the steepness, it’s either inconvenient, or entirely impossible to use sloped areas for building things, walking, driving, or even as open spaces like parks. In dense urban areas, real estate comes at a premium, so it doesn’t make sense to waste valuable land on slopes. Where space is limited, it often makes sense to avoid this disadvantage by using a retaining wall to support soil vertically. As someone born in a completely flat city and now living in another completely flat city (600 m higher, but still flat), I always kinda liked slopes, especially sloped house plots - they force architects to come up with creative solutions instead of cookie-cutter boredom. But I didn't realise how far people's dislike for slopes can go until I saw this monstrosity near Nice (France) while on holiday there: https://goo.gl/maps/zf5H1jSA855bSa4XA https://goo.gl/maps/zf5H1jSA855bSa4XA (you can take a better look in the 3D view). That's right, they must have excavated a whole lot of rock there, and are putting up with a ~ 20 m sheer rock face right next to their houses, just so they can have nice flat plots of land! Ok, it's rock, so probably more stable than a retaining wall holding back dirt, but I would still be worried living next to that precipice (either above or below) - if not for my immediate safety, then for the long term value of my property...
- orthecreedence 5y agoI live on a hill, and the driveway ends below the house, so when we need to haul up materials (gravel, lumber, etc) for various projects, it's walking up a bunch of steps and slippery/muddy hills. I don't mind slopes on their own, and in fact quite like the exercise for every day use, but when you're hauling buckets of gravel or a cord of firewood, it sure would be nice if you could just load up a utility cart and walk it over to where it needs to be (or hell, drive your truck across the yard). It's not possible where we live because of the hill. So I can absolutely relate to why people don't like to live on a hill. And for hanging out outside with friends, you can't beat flat areas. That said, the view is really incredible (we live in the woods) and we don't get water pooling in our place or flooding or anything like that thanks to some well-designed drainage, so, you know, pros and cons.
- jefftk 5y agoWhat makes you think it was excavated from a continuous slope instead of naturally being a near-cliff?
- pomian 5y agoGreat little video explaining all the hidden engineering and technology that we don't see. As with any good presentation, nie we have questions. For example, how do you prevent that slump from happening, that he showed at the end? How did engineers fix those broken highways? Then part two? I assume, would be to show how soil, ground analysis works, with drilling, sampling etc. to define stability, and what engineering used for that.
- h2odragon 5y agoI helped build earthen structures with sharper slopes than 25 degrees 30 some years ago that are still holding back ponds today. "Soil compaction" is the magic that can turn native earth into a real wall that will hold load for quite a long time. The surface treatments, bricks or vegetation or etc are not load bearing, they're a skin to prevent erosion, much like paint on steel. I'm slightly puzzled it doesn't get mentioned here. Has this knowledge been lost? I've not been observing construction work first hand for a while but I don't recall the last time i saw a sheep's foot roller in use.
- Enginerrrd 5y agoI'm a civil engineer, soil compaction is still critical for any grading fill and will continue to be important. One of the biggest issues though is that it can be really hard to compact native material to the required spec. It has to be perfectly within a narrow window of moisture content +/- just a few perce t to achieve full compaction.
- hh28b9b17bf197 5y agoIt is mentioned at 6:32 in the video. As other comments have mentioned though, its not clear that this article is a transcript of a video
- mckeed 5y agoDoes that vary with the type of soil? I wonder if the 25 degrees he mentioned is an average based on the properties of the soil. Either way, you can't really get to an angle that would be considered a "wall" without mechanical reinforcements, can you?
- SECProto 5y ago> I helped build earthen structures with sharper slopes than 25 degrees 30 some years ago that are still holding back ponds today. I think you may be mistaken - note that a "25 degree slope" is just a different way to say a 2 to 1 slope (2 feet across, 1 foot up). I've seen 2:1 slopes used for highway embankments, but earth fill usually specified as a 3:1 slope (18 degrees) - eg when I worked with an earth fill dam (holding back water, same as yours). I've only seen anything steeper (1:1, 45 deg) used a as a temporary (during construction) condition. Sheepsfoot rollers are good for packing very fine material (silt, clay) but not very good for packing larger granular material (i.e. crushed stone/gravel). Silt and clay are very water sensitive materials: each has a very specific moisture content where it can be packed properly, if your material is outside of this narrow range it will not get to maximum compaction (and therefore it will eventually settle). Water moves very slowly through clay so if it is too wet or too dry it's very difficult to get it back into the proper moisture range, and if there's a bit too much sun or some rain between excavation and placement it will not get packed well. The only reason I've seen clay-ey earth intentionally used is for inhibiting water movement, IE an earth fill dam - and even there, it was a secondary barrier if anything happened to leak through the barrier membrane. Crushed stone is (relatively) very easy to get to maximum compaction, and if it sits out for a while and gets too dry you can just hit it with a water truck before placing. It packs quickly and easily, and is stable at the ssame side slopes as earth fill
- jdavis703 5y agoPerhaps this is usual, but when Caltrain was building the new approaches for the elevated Hillsdale station I noticed they were just pouring concrete on top of plants. Maybe not the biggest deal, but I’m pretty sure the engineering algorithms assume a solid mass of concrete. Hopefully there’s enough safety margin that this doesn’t matter.
- LegitShady 5y agovery unusual
- SECProto 5y agoNot usual - what sort of plants? What did the concrete look like it was doing? Organic material would be fine if it was underneath eg, a temporary pathway or something, but that's about it. Actually it might also be fine for secant pile cap (talked about in this video[1]): when you drill a secant pile, you generally pour a concrete cap (that then gets drilled away). [1] https://www.youtube.com/watch?v=UF9FLUioZv8 https://www.youtube.com/watch?v=UF9FLUioZv8
- jdavis703 5y agoI would describe these plants as large, probably seasonal weeds. So it’s not like they were woody trees or anything. Just seemed kind of shoddy.
- programbreeding 5y agoI watch a lot of Grady's videos and there's a comment I've always wanted to make but I don't leave comments on YouTube. I'm going to leave that comment here: it would be great if he spent more time going over the models that he builds and really showing what they're representing. Show it from different angles, show it in slow motion; really explain what's happening and what we're seeing. Note: I haven't watched this particular video yet. He clearly spends a lot of time building high quality small-scale versions of things to show how they work, but more often than not he just shows those things while the voiceover isn't actually talking about what's being shown. Or when he is talking about the thing being shown, it's a very brief comment and then he moves on. I love his videos, but I very often finish them and think "I could have learned more if he spent some more time explaining in detail what's happening with the model, and replaying some component of it several times over as he explains it in more detail."
- spookthesunset 5y agoI completely agree. He spends so much time and energy with those models only to show them for like 30 seconds. He needs a second youtube channel or something where he can show way more detail about these things. Every time I watch his videos I'm always left feeling kind of empty...
- ksml 5y agoJust want to mention that his email is on his blog, and he's surprisingly responsive for having such a big following. I once wrote him with some unrelated questions and he gave me a detailed response, which I really appreciated!
- kjander79 5y agoCan someone explain to me why the brickwork in the picture in this example is just separated columns, using the cap to hold them together, rather than interlocking the bricks? I'm sure that's not the reason the structure collapsed, but once there's movement in the wall, it seems like that would contribute to loss of cohesion.
- hinkley 5y agoHe covered this type of construction in an earlier video, and I think this is the key line: > Gravity walls and mechanically stabilized earth are effective retaining walls when you’re building up or out. In other words, they’re constructed from the ground up. The soil behind this type of wall is supposed to have been stabilized by layering a tension material at intervals to keep it from moving. There's a demo of compacting sand with layers of cloth and then using the cube of 'sand' to support one wheel of a car. The material sags slightly and then holds. My understanding is that those concrete puzzle pieces aren't predominantly load bearing. Mostly they are for erosion prevention and perhaps moisture control (not just keeping water out but keeping the hydration consistent over time and distance).
- hamburglar 5y agoYes, he goes into it in more detail on the video about mechanically stabilized soil, but the techniques used to stabilize the soil mean the wall is entirely stable without the concrete face, and the face is there to keep the soil from getting eroded away and to look nicer.
- cf100clunk 5y agoThe Proctor Compaction Test and its related procedures are absolutely vital to understanding retaining wall capabilities. The article oddly seems to miss such an essential cornerstone of geotechnical engineering. Does an amateur need to know about the Proctor when doing a low retaining wall at home? No, of course not. Does a website called "Practical Engineering" get to miss out on such a fundamental design prerequisite? Not IMHO. Great article and video, nonetheless.
- idealmedtech 5y agoI think the point of this blog and YouTube channel is to make these concepts approachable to the lay person, and introducing lots of technical jargon (relevant though it may be to actual geotechnical engineers) is not the best way to accomplish that.
- cf100clunk 5y agoTime to rename it from "Practical Engineering" to "Popular Engineering"? To me, the Practical handle is significant, so taking a few seconds to explain why soil compaction tests are vital makes practical sense.
- dsshakey 5y agoThe practical in his videos probably refer to the fact that he always explains things in physical models. It's very rare to just be theory. Thus, practical engineering demonstrations.
- throwaway0a5e 5y agoFor thousands of years retaining walls were successfully constructed without more than a cursory understanding of soil compaction and they didn't have rebar or geotextile to help them. Nobody needs to understand soil compaction if they're willing to move and expend way more material than the bare minimum in order to solve the the problem. This is true in a lot of subject areas. You don't need to understand a lot of things if you're willing to copy what is tried and true and can tolerate some inefficiency. For almost all personal and commercial projects the material is going to be cheaper than paying a real engineer to poke the soil with a calibrated poker and plugging the numbers into a spreadsheet that has some formulas.
- irrational 5y agoThank goodness for the red circle in the top image. I totally would have missed the collapsed retaining wall otherwise.
- aidenn0 5y agoI'd be interested in seeing diagrams of things soil nails, I'm having trouble visualizing them from the text description.
- LegitShady 5y agowatch the video at the top.
- aidenn0 5y agoThe video didn't show up for me
- LegitShady 5y agohttps://www.youtube.com/watch?v=--DKkzWVh-E https://www.youtube.com/watch?v=--DKkzWVh-E
- aidenn0 5y agothanks!
- northisup 5y agoI believe these are just referred to as "walls" as they failed the "retaining" portion of the exam.
- culebron21 5y agoThe beginning of the article sounds so modernist mid-20 century, I couldn't stand that. Old roads that formed on old paths are much more stable because people went where the area was dry, and then dirt roads were stable and didn't move down or cause rain erosion. The generalizing phrase, that terrain is just an obstacle that should be plowed through, is laughable. People lived very well without retaining walls and without such huge excavations, until transport engineers decided to please cars, and not slow them down, or not make them go too steeply. Same for the sentence about buildings. There are plenty places where slopes are taken adavtage of. In Stockholm, there are some houses that have +2 storeys on one side, and entrances to 3 storeys from different sides. In my town, a mall built in 1960s has 2 storeys, the top one can be entered without steps at all. In Finland, they used sloped ground to build stadiums, and even to make basements with windows. People like parks with slopes, children like to ride sleighs in winter on them. The most stupid thing you can do near housing is a flat surface and a concrete retaining wall. That generates more problems than benefits: the wall may float, it may create new concentraded areas of water running on the surface, and mini-waterfalls in rains. This never happens with natural slopes, because with grass they're very stable at 3-10 degrees, unless you concentrate water runoff on them. Finally, the place becomes completely uncomfortable to stay at. It's pretty normal to lay down on a grass on a slope. But unthinkable if there's a retaining wall above you. Unfortunately, nowadays I see the architects and clients prefer not to think and adapt to terrain, but just bulldoze the ground. Otherwise, yes, there are engineering solutions to making retaining walls and making them stable.
- creato 5y agoThere are more people now, and more people means pushing into more marginal areas. And, I'm sure people built roads that sank and eroded in the past too, they just aren't around any more. Personally, I care a lot more about hills when I'm riding a bike or walking. When I'm driving a car, hills don't matter. At the same time, building on slopes can be problematic. It depends on the local geology whether it is possible to do that or not. FWIW, I'm a bit tired of "cranky old guy thinks everyone else is an idiot" posts on HN.
- mega_dingus 5y ago
- julienchastang 5y agoA retaining wall collapsed along US 36, the turnpike between Boulder and Denver, here in Colorado. Poor drainage was the culprit [0] [0] https://www.cpr.org/2021/08/12/us-highway-36-collapse-poor-drainage/ https://www.cpr.org/2021/08/12/us-highway-36-collapse-poor-d...
- mikewarot 5y agoI live in a very flat part of the US. I always assumed that the opposing retaining walls were tied to each other. I'm surprised there's no real anchor to this stuff.
- zie 5y agoThe earth IS the anchor :)
- Arrath 5y agoThey can be tied down, actually. It all depends on the designed bearing load. They're typically called 'deadmen', or tie-backs. See ~4:45 in the video on this page: https://www.thisoldhouse.com/landscaping/21018759/how-to-build-a-timber-retaining-wall https://www.thisoldhouse.com/landscaping/21018759/how-to-bui...
- 60secz 5y agoHad to double check the logo to understand why I was reading this article in Grady's voice.
- ksec 5y agoSaw the video on YouTube and thought about posting in on HN, but somehow I felt Video content generally dont belong to HN, so I am glad there is blog version and getting some attention. I am much more interested though to know why it was already 4 years behind schedule.
- gerdesj 5y agoCiv Eng graduate that ended up in IT here. For home projects, please consider gabions as well as the usual suspects when you are building retaining walls. A gabion is a galvanised steel wire cage say: 4' x 4' x 2' (HWD). They have a hinged lid and you fill them with stones and then wire the lid shut. Sounds stupidly simple, and it is but they have some rather useful properties. Each unit is an easy one man lift, place and fill. Once filled, each one nominally becomes a large single block with great drainage properties. You can wire these things together into long rows. They work very well with water courses because they are easy to fix in place and once filled, won't move. Pouring conc. into formwork is a right old pain in a fast flowing river and it is all too easy to lose the finer particulates before the stuff has gone off (set and cured). You can finish the exposed surfaces in various ways. You can pour soil on top and grass them, pour a bit of low grade conc and gravel for a solid "path". The cages are not particularly pretty but neither are they particularly ugly. If a single cell fails then it generally won't cause much surrounding failure and is easy to replace or repair. You can embed fancy anchors inside them if you have a lateral thrust to resist that can't be dealt with by sheer mass. Sleepers and the like are quite convenient but you must consider drainage otherwise they will rot within a few decades. Block backed brickwork needs a decent brickie to lay them and if they fail it is usually rather bad. I'm no brickie but I've just repaired a broken 3' retaining wall at home and it looks a bit shit. I will be hiring a professional to sort it all out in spring. Here a gabion wall is overkill! I did say home projects above but these things are used everywhere and that includes some pretty huge retaining structures. If you are not a Civil Engineer and need to build a decent sized retaining structure then I highly recommend that you consider gabions first because you are far more likely to get it right first time.
- CoastalCoder 5y agoThe article mentions several construction techniques that rely on steel for structural support. (I don't mean just during construction; I mean in the finished product.) But my understanding is that steel always deteriorates over time, especially when in direct contact with moisture or cement. So does that imply all such structures have a lifespan that's counted in decades, and that maintenance basically requires major surgery to replace the steel?
- abduhl 5y agoHe’s talking about soldier pile and lagging walls in this part. See https://www.coastaldrillingeast.com/capabilities/shoring/soldier-pile-lagging-wall/ https://www.coastaldrillingeast.com/capabilities/shoring/sol... for pictures. There are other types too (sheet pile, drilled pile, etc.). Using these as “permanent” support is usually not done for corrosion reasons as you point out. They can be made into long term support elements but it’s costly and only done when footprint is essentially like in the middle of a city in between buildings. The buildings basement walls are designed for the entire lateral load as if the support of excavation system is fully corroded and gone, so most basements are very over engineered against earth load type failures. Long term is generally 30 to 100 years in civil engineering, depending on when the structure was built. So beyond that life yes it’s a tear down on paper to rehab below grade.
- CoastalCoder 5y agoThanks, that's really informative. So what's the trick with something like the Hoover Dam, where (I'm assuming) major reworking every 100 years isn't acceptable? Did they find some way to avoid steel, or maybe make it piece-wise replaceable?
- lmm 5y agoI think they did it all with non-reinforced concrete, which can last more or less forever. It has good compressive strength but hardly any tensile strength, so they'll have had to design the dam in a way that doesn't depend on that.
- gerdesj 5y agoIf you look carefully at the failed retaining wall it is obvious that it failed at the bottom which is where lateral (horizontal) pressure would be at a maximum. For my money, insufficient drainage was the cause. Pretend that the retaining wall is a dam. Most of the time it has to only deal with soil/subsoil/rock pressure. The lateral force on a soil dam is not the same as water - most of the force is downwards (gravity) which does not affect a dam which worries about lateral forces. However there is a certain lateral pressure anyway. Think about a pile of sand being poured. The sand tries to move sideways as well as building upwards - the sideways bit is the lateral forces on our dam. Water always moves sideways and that's the main difference. However water is less dense than sand. If we don't allow water to drain effectively then we have both a soil and a water dam. Retaining walls that survive a day (ie can deal with initial loads) generally collapse later due to shit drainage or inappropriate "solutions". In my opinion - mostly drainage.
- jaclaz 5y agoYes, lack of drainage is one of the main causes of failures of retaining walls in my experience also, and understandably as the amount of soil pushing agains the wall increases its weight when wet, often more than 20% and water is also a good lubricant to allow for slides to happen.
- anonymousDan 5y agoThis article could really have benefited from some images illustrating each technique.
- macintux 5y agoIt's actually a transcript of the video, so there are plenty of images, not just immediately apparent.
- anonymousDan 5y agoAh! I didn't realise there is a video.
- macintux 5y agoYou weren’t alone!
- lmilcin 5y agoThe shortest answer is "because people like vertical walls".
- jaclaz 5y agoOnly for the record, not really vertical. Usually retaining walls (higher than 2-3 meters) have an outer slope (something like 5%) otherwise they would seem (optical effect) to be falling in.
- lmilcin 5y agoEven you have mentioned that "optical effect" is important. Which is exactly the point. Retaining walls are built for optical effects and looks rather than for being tough. A tough retaining wall would be a slope. Ever seen an old church arch support structure? They are not standing vertically, they are sloped. Sloped retaining walls would not be very nice to look at (they kinda look medieval) but would be much more resistant to lateral forces.
- jaclaz 5y agoI don't understand your point. Retaining walls (generally speaking) are tough enough and do not fail. Those that fail were either poorly engineered/calculated or badly built (or something else in the soils/terrain behind the was overlooked or external actions - like loads and/or vibrations from trafic were underestimated). That is beyond and besides the actual shape and orientation of the wall.
- lmilcin 5y agoLet me give you another analogy. Let's say Macbook keyboards fail much often than mechanical keyboards. Why is that? One could say, the reason they are failing because "they were poorly engineered/calculated or badly built" and that might be true. But another way to state this is the reason they are failing is because we like thin laptops. And making laptops thin pushes the engineering into territory where it is much more difficult to make the keyboard be designed and function reliably. Just like our love of vertical walls makes it much more difficult to engineer retaining walls that do not topple. You see, both of these do not necessarily conflict with each other. They are just different points of view on the same problem. I think that blaming the problem only on engineering is shallow thinking. It is obviously right and at the same time it gives absolutely no understanding of what is happening. It is the same kind of thinking that, for decades, blamed drivers for all accident. Obviously, it is the driver that caused the accident, but it gives no further useful understanding of the problem. Once people understood there are other factors at play some countries started introducing solutions that make the traffic much safer without messing with the driver side of equation.
- beezle 5y agoWas involved in replacing a large failing rail-tie retaining wall, roughly seven foot tall and 100 feet long. Had one engineer suggest unilock with geogrid but after watching a lot of youtubes of failed unilock walls we went with redirock. Eleven years so far including snowy winters and doesn't look like it will ever move an inch.