How to Build a Boulder Retaining Wall

How to Build a Boulder Retaining Wall

I'm at the base of this house, and what's happening, the issue we have today is this entire porch and the decking behind it is sliding down this hill. This is going to be about a 16-foot tall boulder retaining wall we have to build, and what's happening is it's sliding into this lake that I'm standing out on a dock on right now. We set the plan into motion about six months ago. I had an engineering firm come out here, and what we're going to be doing is we're going to be building a retaining wall to tie in with the neighbor's retaining wall starting at this point. It's going to be five foot tall and then as we go, we're going to raise this wall up to catch this porch, to save this porch from sliding in. Then the wall is going to stay at that same height and wrap around and tie into the corner of this deck. To get down here we've got to create a ramp, we've got to create a road so that we can get an excavator with a thumb down here. And as you look behind me right now, this is going to be our road in. We've got to build a second retaining wall just to hold up the road. So you can see how we've got to go backwards to bring the boulders down. Do you know you backed your excavator up? Respondent: He knows what's behind him. Look at that, automatically, look at that, it's like he knows what he's doing, like he's done it once or 73 times before.

Base Boulders

So the pretty big base boulders, we do have fabric that we're going behind this wall, not always, we don't always use fabric. We prefer to use fabric, we have to use fabric on sandy sites, isn't that right Tim? Clay sites, it's questionable because a lot of times what happens is the silt from the clay will bind up in the fabric itself and then create hydro-static pressure and cause blowouts or ruptures. But anytime we get a chance, we're going to use fabric behind it. Now in this wall we're actually using Geogrid as well, you can see where he's got the grid laid out and that goes in horizontally every two feet and then we angle it up. We've got the 33 inch commercial Ram X-Packer, that's actually ours, we bought it from a rental store. But you can see that's how we get all the compaction behind the wall so it's not just soft soil going in place, and then you can see how he lays this out like a jigsaw puzzle. It looks like he's using a basket weave pattern on this job site, any particular reason? Does the customer want that, or? Respondent: No

Random Boulders

No, just what he prefers, that's what's working. He can throw a random boulder, and this would technically be considered a random boulder. This big bottom one here. Sometimes what I'll do is I'll put them up vertically just to break up the pattern a little bit.  But I think this is a pretty good-looking retaining wall and it's going to keep that deck and the rest of the house from falling into the lake. So it looks like he's making some good progress, especially for the rains we've recently had. And after this wall gets built up then it's over to the other side and then we're out of here. What do you think Tim, two days? Respondent: Yes, two days overall.


The grades are a little bit deceiving in this case; it's tough to tell. But we have about a 16 foot drop, hence that's why we're going to need a 16 foot tall wall. What you're going to find is when this project is done you're going to see a retaining wall that cuts through here and then it wraps up and then it wraps around and then it hooks into the corner of the deck up there which allows us access to come straight down through the middle. The customer has had no access to this lake with anything but what he could carry in his own two hands.  They will no longer have steps. He's going to have a nice ramp that he could drive a boat down if he wanted to. Or he could drive a lawnmower down here and do maintenance.  He can gain access. So we're going to crawl up this hill and I'm going to show you some of the equipment we're going to use to tackle this project. A job like this takes 3-4 weeks. You want to do it right. We've got about 400 cubic yards of structural fill soil coming in.  We've got about 2,000 square feet of boulder engineered boulder retaining walls that we're going to be building on this site. Not just boulder walls, but boulder walls fortified with a 3.0 Geogrid.  Certified, stamped, gone through licensing, permitting, gone through all the requirements surveying with the city and approved.

Daewoo 75

Here's the machine we're going to use. It's nothing more than a Daewoo 75, but the key component to build these walls the right way is the attachment. He can grab a boulder with this attachment, pick it up, and spin that baby 360 degrees.  So he can take a boulder and put it anywhere he wants it. Without that attachment, you couldn't do a job like this. We're going to be using four-foot boulders as our base. When you're using a boulder that's big enough to sleep on, that puts it in perspective. These things are gigantic. We're going to be using three-foot boulders as secondary courses, and two-foot and 18-inch boulders for our tip-top course. You can't build a structural retaining wall using the smaller stone because this is not technically a landscaping job.  This is a structural retaining wall. Those smaller stones they're awesome for smaller projects. There is a time and a place for them. When you get involved in a project like this that you're holding up a house, you have to have the right tools and materials.  You've got to have the right plans. You don't lick and stick. We've worked on this project almost 12 months. We're going to show you the process.  


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