Why Boulder Retaining Walls Fail

many boldly retaining walls are in a state of failure because the contractor built the retaining wall the wrong way in this video we're going to talk about the fundamentals of building a boulder retaining wall and why these simple principles or you fail your factors are the size of the boulders typically used and then how those boulders actually get laid into the bank you know what we're looking at is we've got a decent four-foot Boulder laid the right way another Boulder that's kind of walked in in general boulders make an absolutely phenomenal building material they never suffer from weathering or erosion salt degradation has absolutely no impact on and the sheer weight of the boulders allows them to tolerate massive amounts of Earth movement without ever transmitting that through the retaining wall and into a state of utter failure that is when they're built the right way so let's start talking about how boulder retaining walls are typically built the wrong way you cannot build a retaining wall like that and I'm gonna look point go right down the point this Boulder right here specifically we got this nice four quarter blade the right way the depth is maximized into the slope but beneath it look at this thing it ends right here there's no depth that Boulder if it was to be used where it is needs to be rotated and laid into the bank this wall was built to maximize feet now here's a protip contractors will usually buy boulders on a price per pound but they will usually charge to install the boulders on a price per square foot what this means is big boulders cause big bucks but that doesn't always mean you get the most square footage out of those big boulders that's where the big issue comes in and that's a lot of big words now the first rule with boulders is bigger is better with this in mind contractors will usually try to install Boulder retaining walls using stones of inadequate size for what they must retain this means that the songs stones are simply too small the strength of a boulder retaining wall and its overall holding capacity comes from the sheer weight of the boulders being used small stones simply can't hold back big banks the second misapplication when building a boulder retaining wall is using a large boulder but using it in the wrong way boulders are by nature very irregular in their shape and size meaning that they will have typically have a small side and have a big side here's another great example these are phenomenal stones in and of themselves like here it is signed by Paul I can reuse every single Boulder here but I'm not gonna be using it for its face I'm gonna be reusing it for it step this Boulder right there we rotate it 90 degrees get the depth into it not the face surface area but the depth this Boulder right now probably has 6 square feet face by the time I'm done using it we'll be lucky if we get 2 and a half 3 because it's not a very thick stone this way it's gonna be deep into the bank which is gonna resist movement oftentimes contractors will try to put the big side on the face of the actual retaining wall but the strength of the retaining wall lies in putting the big size into the bank one Boulder may have a face that is 8 square feet and have a side that is 4 square feet now the contractor is going to try to optimize the square the face square footage of that stone so instead of putting the face square instead of putting the big side into the bank and burying it they're gonna flip that and they're gonna put that into the face so we are at the site of a failing Boulder retaining wall probably 10 footer and great boulders they use awesome stones but the construction itself how they put it together where this front wall has its main issues you can see that they were optimizing the face of these boulders instead of giving it sit of having a boulder like this they use the big face area that should have been flipped sideways so it went into the hill because now there's nothing behind that push holding it what's happening is here's a great example wide open there's nothing back here pulling this one to that one and the soil behind it is pushing it out even bolder retaining walls need to be engineered when they're over four feet although typically you can build a gravity based retaining wall much taller with boulders than you can with a modular block Boulder retaining walls also will need a certain amount of drainage and base material depending on the subsoil conditions but if your soils are soft and compression of all you're going to want to fortify that base by laying something down before you put the boulders in place we're gonna talk about filtered fabric right now we're gonna dispel some of the myths boulder retaining walls in certain applications will require filter fabric and at other times you will not want to use filter fabric yada-yada-yada you have very sandy soils with very little clay binder behind it it is mandatory that you put filter fabric it or the soils will wash through the face of the boulder retaining wall but if you have a high clay content soil with a lot of silt within it beware that when you put filter fabric behind that Boulder retaining wall that fabric is going to plug up plain and simple and when that fabric plugs up it's going to start to bulge outward a way to get around it if you have a high clay content soil and you're willing to do some work is to plant the heck out of that retaining wall it's almost like stitching the boulder retaining wall together those plants will stop the soil from weeping from eroding through the face of that retaining wall and furthermore it will literally knit everything together actually creating a stronger retaining wall in the end than if you build a boulder retaining wall with just fabric alone you obviously want to be cautious when applying filter fabric it is not a universal one-size-fits-all application so let's repeat this high clay content soil you don't want to do anything with the wall you put fabric behind it knowing that that fabric is gonna bulge sandy gravelly soil something that doesn't have a clay binder in it you put filter fabric in because that filter fabric has to retain that sand from eroding through the base but if you have a high clay content soil and you're willing to do some work on your own don't put filter fabric in but plant the heck out of the joint spacing eventually those joint spaces will grow over and will create a stronger longer-lasting retaining wall hands down hey one last thing look me up on Instagram the majority of my projects do not make it to youtube I do almost daily updates on my Instagram

Channel: Stanley "Dirt Monkey" Genadek

Views: 393,455

Keywords: retaining wall, retaining wall construction, Landscaping, retaining wall on slope, retaining wall ideas, retaining wall installation, retaining wall drainage, boulder retaining wall, boulder retaining wall construction, how to build a boulder retaining wall, retaining wall design, diy retaining wall, do it yourself retaining wall, how to, diy, rock retaining wall, rock retaining wall construction, natural rock retaining wall, building rock retaining wall, stone retaining wall

Id: cRWwCXhVZaw

Length: 7min 21sec (441 seconds)

Published: Fri Jul 15 2016