With any construction like your foundation is going to be key. You’ve got t have a good foundation. So if your existing current soils are may clay-based or just pure, like pure gravel, like really rocky gravel that won’t pack very well. Basically clay and gravel and then top soil, it’s all black dirt, you want to get all that out of it. You want to get down to a real good clean, sandy, you can have a little bit of clay in there, that’s not going to hurt, some cases it’s going to help tighten things up when you pack it. But you’re going to want a really good base as with anything when you build the foundation or a frame, or anything on any type of construction.
Best Practices for Building a Retaining or Boulder Wall
So you want to put your largest boulders on the bottom because they go the most mass, they can hold the most weight and they’re least… They’re going to have the least resistance to actually move when it comes to things like frost, may be you bump it with a tractor when you’re mowing the lawn. A tractor is not going to bump or move a 3000 pound boulder, but frost will potentially move that boulder. So you want a really good foundation.
And you really want to set the bottom boulders, you can see in this picture here, how a lot of these boulders are set. Not only to aesthetically look good but more importantly this bottom round boulders was set to serve as a locking foundation. So they’re erratic meaning erratic, there’s no general shape or the size is consistent, meaning they’re reasonably about a 3000 pound boulder each. But the shapes of them are different erratic boulders and you want to interlock those boulders so that they actually create like a puzzle piece where it’s very strong. Once it’s locked in and stacked on top of each other and then back filled and creates an extremely strong wall.
So you want the boulders to really go into the ground, so a lot of times you could set rocks or set boulders to only serve the purpose as a visual aspect and use a larger face of the rock. You got to be careful, you can do that in some scenarios and in some cases, but a lot of times using that larger face is going to put less weight or less surface area of the rock either on the bottom, meaning where the weights at or in the back, in the dirt. You want a lot of that surface, you want it to lock in basically, is what you want to do.
So that’s the overall like general construction practice of it. If you want these boulders to lock in place as best as possible. And there as with erratic shapes it’s just like a complete art game, you got to fit them in, you’re back and forth so with some are going to fit right some won’t, you might have to it apart a little bit. And it’s really important to work with either home owner, you the home owner or work with the builder and make sure that us your building that wall, it’s really looking how they want it to look. Because you can build the wall how you want it to look, in the end, and think it’s great and they may not be happy with it and that’s either your time and material to more cost for the home owner or it’s re-work over for the contractor, for myself. So it’s really important to work with the homeowner and work with the builder on how they want that wall to look. If you are doing an engineer wall just follow the print, it’s pretty standard that way, engineer walls are really completely different.
Special Considerations for Boulder Walls in Northern Michigan
So the other important factor to use with boulder walls and I think this is more really in Michigan, a practice that should be used by everyone. It’s not though, I have seen a lot of boulder walls and I’ve seen them fail fast. There was one built last year and it’s already failing. But you’ll notice that’s there’s this black material, landscaping fabric, it’s really heavy duty fixed up. But the black material serves as a barrier to prevent water from washing out sand and small debris through the rock wall. So having that fabric there prevents that, no matter what unless it’s pure clay or even if it’s really good gravel, like if you actually back fill the boulder wall with pure gravel, like road gravel, you’re still going to have wash outs back there. And it depends too on what kind of overall material is the soil made of, where is the fall, where is the grade going to, where’s the water flowing, all that, there’s a lot of variables for that.
For the most part, always going to use landscape fabric behind the boulder walls, compare to cost of the overall boulder wall, it’s very cheap, simple effective way to ensure that, that boulder wall is never going to leak. And I say leak, never going to have sand leak through it and just going to preserve and make that wall last even longer because what happens, you don’t put those, that fabric behind that boulder wall, water will begin seeping through and bring sand with it, and you’re going to have either sand or debris on say, your patio or falling on to your lawn, your driveway or whatever it may be, and then eventually it’s going to create a sink hole behind your boulder wall and it’s eventually going to cave a lot faster than it would without having fabric in place. When you have a boulder wall that will last, a life time, a hundred years, no problem.
That is really the basics of it, you want to a back through with good clean material that’s going to drain well like sand or a gravelly sandy mix so that, that water falls down behind that wall. Depending on your slopes behind the wall, you’re going to want that water to wash away from the wall, you want the water to go away from the wall. As you can see in these pictures here, there’s a mound. The water is going to go towards the – the rain water will wash off towards the lake water and then it will also wash off towards the house and around under the lawn into the grass. And with that landscaping there, anyway, a lot of the water is just going to get soaked up, saturated by the plantings and also the moulds, decorative mulch that’s placed out there.
So those are some of the basics that you need to consider when having your contractor build a boulder wall for you. If you’d like a free quote or estimate, feel free to give Avery Excavating (myself) a call.
We serve customers within a 35 mile radius of Traverse City including: Sutton’s Bay, Glen Arbor, Kalkaska, Elk Rapids, Williamsburg, Kingsley, Acme, Benzie, Empire, Lake Anne, Lake Leelanau, Torch Lake, Elk Lake, Glen Lake, etc.
We look forward to helping you out very soon. Call: (231) 714-0844