Engineering trick to strengthen retaining walls, and rock delievery

Hey, welcome back YouTube. Today we're actually going to talk about an engineering trick to increase the strength of your retaining walls. This is actually a trick that can increase the strength of your retaining walls by two orders of magnitude. That's right, you heard me right, a hundred times stronger in shear force and in tension. So stick around. However, first we've got our last load of rocks coming in. I got the drone out and check this out. All right, everything, whether it's a pile of sand, a pile of rocks, or just a hill made up of roots and soil and grasses, will have a natural angle that if anything's steeper than that angle, gravity will cause the particles to fall down. This angle in engineering is called the angle of repose. Now if I dig down and make this angle bigger, rocks will naturally slide off and rebalance that angle of repose. It'll slide off and rebalance. Stuff like this can exist only temporarily until soil gets wet, rains happen, the soil gets liquefied and it will get disturbed and it will re-assume its natural angle of repose. So how can we have a retaining wall that has a straight vertical cut into it without worrying about a landslide? Let's talk about the physics of what's going on in there. This rock pile right here is perfect for illustrating the point. You can see that it's got a natural angle of repose. Now if you think about soil, and all soil is essentially just different sizes of stone, whether it's sand, silt and clay, it's just a different size of stone. So if you think of what's holding these into the hill, it's actually gravity is pushing down on the rock and whatever it's touching is pushing back with a normal force. Now if there's an angle to the hill, then gravity is pushing down and the normal force is applied this way. Friction is holding it, the sliding friction between two rocks is holding it and if the hill component gets too steep, then the natural reflection force, the natural force is going to get pushed further out there and the horizontal component of that force gets larger. If you picture just a natural flat driveway, the normal force resisting the gravity force is straight up. As I enter into this hill, the hill, the steeper it gets, the natural force gets pushed more into the horizontal. Once that horizontal component of that force oversees the friction, the sliding friction between the rocks, and that component becomes stronger than the friction holding it back, the rock's going to tumble down. So how can we use a trek in order to kind of cheat our way into a The answer to that is actually very simple. Composites. When you think about any kind of composite structure, it's typically stronger than the aggregate structure of the components that it's made out of. So for a retaining wall hill, if we're zooming in and under a microscope, and this is a single sand particle for example, if we can put a sheet of fabric on the rock, on the hill, and then we recover it with soil, and then we come in and we get a foot of soil, and then we put a new sheet of fabric, so we cut and we put a new sheet of fabric, and then rocks and soil on top of that one, then what happens now is when these two rocks, when these two rocks want to slide apart, then actually what we get is previously there was basically nothing holding these two rocks from sliding apart. There's no force holding that back. When we put a layer of fabric in, this fabric now, if these two rocks want to slide apart from each other, and this fabric should be exactly perfectly horizontal, as close as you can get it to horizontal, then when these rocks want to slide apart from each other, because there's weight of the soil on top of the fabric, when these try to slide apart, the fabric itself is being stretched, and it's going to be in tension, and it's going to try to pull these rocks back together. So now let's go back to this hill here. We're going to layer and level out a flat area on this hill. It's hard for you to maybe see, but that is flat, and we're actually just going to stick this tiny little piece of fabric right in there, and we're going to cover it back up. So now the piece of that hill with no fabric, I'm going to put a vertical force down, and you can see that the stones want to pull apart from each other. I'm going to kind of go like this, and you can see the stones want to pull apart, and they're going to slide down, and they're going to find their angle of repose. Now this piece without the fabric, when I push down, the hill is not sliding away at all. It's very stable, and even if I drag apart some of this soil and make a new angle of repose, you can see actually it's holding pretty well. Now it's not going to hold perfect because there's not multiple layers, there's just one, but every single additional layer you can put in, this fabric is resisting these rocks. These rocks are being pushed down. They want to fall apart, but this fabric is holding it together. We're going to do that on the other side of the pond. Now as this is right now, it's pretty solid. It's got some massive rocks, it's got large cedars, and it's got these posts, but if I have a trick, I bet your butt I'm going to use it. So here it is before we get started. We're going to dig this down a couple feet. I'm going to cut some strips of fabric out and lay them, and remember you want them as horizontal as possible. So I dug down about a foot, leveled this valley out. We're going to stick a piece of fabric in here and then recover it up with soil, and then we just put a piece of fabric down. After I took this photo, I actually dug the edges down and made it a little bit flatter. You want it as close to horizontal as possible. Then I extended it into the hill, put the dirt from here to the left there on top, put a little dirt on the edges of the other fabric, and layered this fabric on top of that, and they're both at the same level. Then I recovered both with soil. I ended up building up a little bit more soil of this after there's about six inches here, and it ended up roughly about a foot of soil on top of this, and then I tamped it down. The tamping is just going to help everything bind together. After adding about a foot of soil, the soil level was just underneath this pipe here, and what I actually did then is dug underneath the pipe and extended it back into the right of the hill, and ran another strip completely that lengthways. I wanted to anchor this next layer as far deep into the hill as I could get it. Most importantly, this is one long continuous piece from the edges of the logs all the way back into this far deep into that hill as you can see. I didn't want to dig too close to the rocks because I didn't want the rocks to fall, and then I tamped it down, and you can see this is only two layers, but there's roughly a foot of sand between each layer, and then a foot on top of this layer, and this is just going to hold in so well. And then the final component to this is planting soil stabilizing plants like vetiver grasses, normal grasses, ground cover, sea buckthorn, and the tensile strength of all the roots will help hold and stabilize this soil. So this is over engineering 101. So obviously the more layers that you can weave in, the better. I didn't want to go down too far because I was kind of getting in their ways. I just wanted to add in, you know, like I said, if I have a trick that I can use to strengthen it and over design it, you know, maybe it's just my career that I do working at a nuclear facility, but we over engineer the crap out of everything. Huge safety factors. So I want to do the same thing here. If this thing fails down the road, I didn't want to ever think, you know, while I had everything exposed, why didn't I just get in there and dig and put the fabric in? So I did it. I feel better. I got two layers. I'd like to have done like three or four, but, you know, two is going to be way better. It's going to be three times as strong as it would have been otherwise. So thanks for watching. Stay tuned. Tomorrow, hopefully, maybe in a couple days, we're going to get the wetland filter. It'll be all done. I'll stitch together a video on, you know, what a wetland filter is, why you want it in your pond. It's extremely valuable both for insect habitat, fish nursery spawning. It's like the perfect place for that. Bird feeding, but mostly for just like biological filtering and scrubbing, not just of nitrogenous waste, not just of fine sediment particulates, but also chemicals that might run off and go into your pond. So it will scrub all that out, hold it in biological material and very, very valuable thing that you can do in any kind of pond setup and stick around. I'll talk more about it in that video. Thanks for watching.