How to Build a Retaining Wall and 6 Reasons they Fail

Today we're going to cover six big mistakes when you're building a retaining wall and how to avoid them. So, let's get this wall would fail over a year ago in this exact spot in this exact way. Look, you can see where the grades behind this wall have dipped down. It's going to blow that wall out. In fact, we had one catastrophic wall failure on this project last year. We had to repair it. We got another one coming up. It's not because I have a crystal ball. It's because the writing was on the wall. It's just completely shot right there. That's from drainage, from not maintaining it. You can see where all the grades have dropped down in here. And now we've got big sink holes behind this retaining wall. I can literally stick my leg down in here up to my knee. You can see the distinct angle. It's all bowed out. This problem could have easily been avoided had the property owners, the development company listened when I screamed my head off. All you need to do is either a raise the height of the retaining wall up just tall enough to direct the water that's coming down from the other property away from this one spot and divert it back onto their own property or B create a burm above the retaining wall which keeps the water from funneling into this location. Two simple fixes not done in time. Retaining walls come in all shapes and sizes. Some of the absolute strongest retaining walls made are actually poured retaining walls. To remove a retaining wall like this, we're going to be outfitting the front of this skid loader with a jackhammer and pounding in the front just to soften up the concrete. Why is this wall so strong? Well, it's how it's designed. It's one continuous element. This has a lateral footing down at the base of this soil keeping the retaining wall from tipping over. It's all about the base. And they know how to build them 100 years ago. Now, if you're building a retaining wall today, you make sure that you design the retaining wall for the exact type of material that is going to be on the face. That means if it's a modular block retaining wall, you got to have the right drainage. You got to have the right geogrid. If you're using a boulder retaining wall, you got to have the right size stones. It doesn't matter what material you build a retaining wall out of, you've got to design it to withstand the elements. This is a great example. Here's another typical problem with retaining walls. People rely on the drain tile to actually function. The wall behind me, it looks okay, but it's actually in a state of failure. The first sign that it's in a state of failure is if you look at the base of the wall, you can actually see where the drain tile opening has water percolating through. That means that the water in this entire retaining wall is concentrated into that drain tile system. That's just a 4in perforated drain tile. It's not meant to handle large amounts of water. It's meant to only act as an emergency overflow at best. The entire retaining wall should allow water to pass through evenly. Meaning the water in the behind the retaining wall should never get down to the drain tile system. If you see water pumping through a drain tile opening, that means that entire wall is in a state of failure. All of the drainage aggregate is bound up. It's not allowing the water to pass through and eventually this wall is going to pop like a balloon. Behind me is a small portion of a 30 plus thousand square ft retaining wall we built over a decade ago. Now even though this company devel invested millions of dollars into the infrastructure of this property, they failed at one important component and that's maintaining their retaining walls. And the most important and easily upkept thing that you can do on a retaining wall is to make sure that the grades stay flush behind the back of the block. This is a great example of what happens when you allow the grades to fall behind the wall. They're going to find cavities. I can reach in and put my whole hand inside this cavity behind this retaining wall. And you can see other cavities and that's going to create premature failure in in this retaining wall. Often times I see retaining walls, even massive ones like this, get neglected. And when that neglect sets in, failure will rapidly occur. So what you can see is they've actually allowed the vegetation to grow right through the face of the retaining wall. That's how far the neglect has gotten on this site. What happens when that vegetation grows through is it creates gapage in the blocks. As the as the plants grow, the roots expand and they create spacing in the blocks. That spacing is a cavity for the aggregate behind it to flow right through the face of the retaining wall. That also creates funnel points where the water is going to want to migrate instead of dispersing evenly behind the retaining wall. It's now going to find a spot and it's going to puncture through that retaining wall, creating potential issues during heavy rainstorms. Here's another great rule of thumb that you can use on almost any retaining wall. You want to plant a major tree, bush, or shrub on it, like the pine tree you see behind me. Take the height of the retaining wall. Now, in this case, it's just a 5-footer, but multiply it by two. So, that means take the height of the wall, 5 ft, * 2. That means you go 10 ft behind that retaining wall before you would plant this tree. If you plant it too close to the wall, what happens is as the tree grows up, it creates undue stress and that's called a sir charge onto the retaining wall itself. So, as the trees growing up, the roots are growing down, it's going to push that wall out. But if you use that rule of thumb, that should put you safely outside of the searchcharge zone of most structural retaining walls. Here's another myth for you. Pock or sand makes great back fill material. Nothing could actually be further from the truth, especially in the drainage zone. You want a dedicated material that is angular in nature, can lock together, and doesn't have a lot of fines in it. The stone of choice I use is 3/4 in clear rock. The reason that's important is because as water flows through it and through the base of the wall, it's not going to move. it can resist all types of ground movement behind the wall and not transfer that into the actual face of the structure. Today we covered six issues that typically make retaining walls fall apart, but sadly there's a lot more reasons why they fail. Let me know in the comments down below if there's any specific videos that you guys and gals would like to see. God bless and go get them.