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Gabion foundations

Threane


Just wondering if anyone had any examples of or insights into the usage of gabions as foundations for buildings.

The hypothesis is that it could serve as a relatively easy and secure technique for elevated structures, the gabions being porous enough to allow water to drain through it, underneath the building.

I'd be inclined to experiment with some kind of rebar perhaps, rather than the sort of wire mesh you see in other gabions that are used for either decorative or retaining purposes. But I've never actually built one before, nor have I ever welded anything. 

Ideally, it would be around a 140 square foot building, perhaps a sort of dome, that would be built upon any such gabion base. All still hypothetical, of course.

And it would be built upon a sand/dirt/rock terrain in the CA desert near Joshua Tree. 

More broadly, I'm looking for building techniques that don't require heavy machinery (aside from a welder in this case) or construction vehicles. Stuff that can be done by a single person.

 
Jan 9, 21 2:14 am
justavisual

check how they build dry stone walls in corsica

Jan 9, 21 9:05 am  · 
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apscoradiales

As long as bearing capacity of the soil, as well as the gabion wall itself, is sufficient, I don't see a problem. Not sure rebar would would much as long as the cage is solid enough.

I would check with structural engineers, though. As this is being contemplated to be built in the desert, I don't see a problem with frost or water saturation.

Jan 9, 21 9:17 am  · 
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Threane

You happen to know if there's a forum for structural engineers?

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apscoradiales

No, I do not. Might want to Google it. If you're going to build something like that, you will have to spend a few dollars on a structural engineer anyways.

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Threane

Awesome thanks

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rcz1001

If the gabion 'cage' is sufficiently holding the rocks together, that would be a starting point. People mentioned soil bearing capacity which is a must. You may want some mechanism for securing your sill plate of wood-framed (or similar light metal framed) walls to the gabion foundation. I have explored the idea but it is something that is going to require a bit more thinking out the design. I would more than likely use the gabion for interior bearing walls and maybe some other type of foundation wall system for the exterior perimeter. I would recommend limiting to 1 to 2 stories (up to 12 ft stories) above the gabion. The gabion may wall height (if starting below grade as a basement story) of up to 10 ft. in height but the gabion wall thickness would likely need to be about 15-20" (maybe more if we are talking significant retaining wall functionality is involved) thick with a good and very secure 'cage' that won't rust and corrode. That will be something you need to pay attention to in considering longevity for bearing purposes. The cage is what keeps loose rocks together. If the cage fails, the rocks aren't held together because they aren't likely to be shaped like in a well-built stone masonry wall. Even drystack walls, there is thought in shaping (as needed) and placing the masonry units so they are secure. It isn't just a pile of random rubble because in order for that to work, requires mortaring. The idea behind gabions is it eliminates the use of mortar very significantly. Another benefit is you can tie multiple gabion units together so they work as a unit so there is some interesting seismic stability potential. This is partly why it piqued my interest because I am in a Seismic Category D (D2 in IRC) zoned property. It isn't something I have seen or heard of a lot of people doing yet despite we are in an area where rocks are common place. Typical bedrock material makes for this use. We can limit use of concrete/cement material.

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Threane

Great stuff here, especially the point about making a larger frame to contain the gabion cages. I'd be inclined to try some kind of square steel tubing, but I haven;t worked with any of this before. Also maybe filling in the empty spaces between rocks with some sort of gravel? Not sure how meaningfully that would help support.

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rcz1001

Use a finer mesh material when using smaller gravel so they don't sift out. Normal cages would have 1 or 2 inch squares for larger rocks but a smaller metal mesh of a 1/8" to 1/4" squares to fill in-between the larger squares in order to keep the finer gravel from getting out. The mesh openings needs to be smaller than the gravel size used. That is something I would suggest.

1  · 
Wood Guy

I think the limiting factor would be the cage design. For longevity, I'd want a relatively large diameter, corrosion resistant steel.

Jan 9, 21 10:49 am  · 
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Threane

re: dry stone walls in corsica, this what you had in mind?


Hadn't looked into this before. I only just started building a rock and concrete retaining wall, and already its clear that waaaay more concrete is needed than I had assumed.

Jan 9, 21 11:21 am  · 
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apscoradiales

There are literally thousands, if not millions, of such walls all round in the Mediterranean countries. Unfortunately, you have to know one of the languages from there to understand the methods and principals behind building them. I just googled them, and article popped up written by a professional engineer - albeit in Croatian.

Such walls were used as property walls between various fields, as well as for protection against invaders and to keep the livestock from wandering away. They required a lot of work to put up, and they make up the character of the region.

1  · 

Re: the amount of work required to maintain these and using them as property delineation ... check out the poem “Mending Wall” by Robert Frost. “Good fences make good neighbors”

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The closest example i have used is rammed aggregate piers.

The use of the Gabion cages for a building is tricky as the weak link is the cage wire rusting out and the stones coming lose.

The forces that a foundation set on rocks needs to overcome is compaction and then we also need to constrain the rocks so they don't slide out of place. Gabion is often relatively large chunks with nothing filling in so there is a lot of air in it, erosion can break down the larger rocks and cause settling and the surrounding soils can wash into the gaps.


Just my thoughts on it

Peter N


Jan 9, 21 6:04 pm  · 
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Threane

Yeah I'm with you, and my mind goes to some kind of higher gauge metal to make the cages out of, but again I really don't know where to start there.

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natematt

I have tried to use gabions for atypical things before and it was a pain. Assuming you're getting some kind of permit, this seems like it would be a challenge in CA, unless someone has done it before. This seems like it might be poorly suited for earthquake anyway, if you think about the logic of it. 

Here are a few alternate thoughts for a small elevated structure. These are not recommendations, just ideas since you asked. 

You ever hear of a rubble trench foundation? I think FLW used them sometimes. I wonder if you could do something like that and then use CMU and an elevated wood floor for a no-concrete approach? Really don't know that much about it, but just an idea. (same concern about the earthquakes as the gabions though) 

You could conceivably do screw piles, though based on personal experience this would likely have issues with plan-checker in CA as well. Anywhere else this would seem like a golden idea to me. 

A more typical approach if your soil allows would be to use pre-fab concrete piers, again depends on your soil and requirements since you probably don't want to have to haul huge piers, and too many piers would be more challenging for differential settlement. 

And the most concrete (pun intended) approach would be to just give in and pour a little concrete yourself and do wood posts on concrete piers/footings with an elevated wood floor. Did this on a project in SoCal. Had decent soil and supported a fairly tall 300ish sqft structure on 4 posts attached to 4 2x2x2 conc footings. 

Another thought while we're talking about unique approaches is the whole concrete-free slab on grade assemblies that some house-builders use. Seems like some glaring flaws. to me, but I've never used them... So I really couldn't say 

Interesting topic. 

Jan 10, 21 4:39 am  · 
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Wood Guy

I believe I was the first to do a concrete-free slab--at least I don't know of any who did it before I did, in 2017. I've done a fair amount of promotion about the idea. It's not ideal for every situation but I'm happy to respond to any questions or concerns. I just talked with an architect two days ago who wanted more info to convince their builder, and said it will save as much as $15K on their project.

1  · 
Wood Guy

I realize my comment above seems braggy. My client wanted the lowest cost, high-performance foundation/floor system, and my friend Steve Demetrick had recently written about skipping the slab in a basement, placing Advantech directly over the foam and vapor retarder. So we just developed a system to do the same for a slab on grade.

1  · 
natematt

That's pretty cool! I first saw something about this in early 2020, and thought it sound ed interesting, albeit a little iffy, Sounded like they had been doing them for a couple years so as far as I know i haven't seen anything before 2017 like that... so maybe.

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Wood Guy

I got everyone I knew who had done one together for this discussion: https://youtu.be/iGXoAN4znTI.

1  · 
apscoradiales

Wood Guy,

So you compact the dirt, is that how it's done? Do you you put a compacted gravel base below the dirt? Any insulation? I imagine you would do a soil investigation first to make sure there is no underground river nearby? Do you put a vapour barrier immediately under the floor finish? Can you put a hardwood floor or porcelain time over compacted dirt? How does one deal with water in case a pipe bursts? Would not the dirt soak up the water casing massive damage?

I've been to some very old houses in Europe where they had dirt floors, but they never took it further and made it more technically advanced with fancy finishes.

Jan 10, 21 11:32 am  · 
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Wood Guy

Aps, I wrote about it here: https://www.finehomebuilding.com/2019/02/27/minimizing-concrete-in-a-slab-on-grade-home and here: https://www.greenbuildingadvisor.com/article/minimizing-concrete-in-a-slab-on-grade-home. A builder I know did his own version: https://www.greenbuildingadvisor.com/article/another-take-on-a-concrete-free-slab, as have my friends Steve and Jake: https://buildshownetwork.com/blogs/dirt_slab.

Basically the prep is identical to what you would do placing a slab with frost walls or grade beam for a frost protected shallow foundation, with the addition of a 2" layer of 3/8" tumbled stone as a screed layer under the foam insulation. 

There are probably other ways to do concrete-free (or reduced-concrete) slabs including compacted dirt. My approach is for high performance homes with wood or tiled floors. If people like exposed concrete, that's still the least expensive way to get a high performance foundation.

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apscoradiales

Thanks.

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mightyaa

Gabions would be a terrible foundation.  One purpose of a foundation is to keep 'the outside' out.  Insect control, thermal, moisture, plant life, varmit, etc.  Look at shallow foundations; PT slab, turned edge, etc. Other issues is you know you have to physically attach to your foundation right?  Sort of hard to get a structural anchor to a stack of stones.

Grouted cobble foundations (which would be called a masonry stone foundation), grouted stone and 'real' masonry, and even wood foundations are a potential alternate. Oh, and those stairs you show; code violation and a huge trip hazard.  (uneven surface, voids are too large, etc.)  

Jan 11, 21 7:50 pm  · 
2  · 

I'm not sure those are intended to be stairs. More likely part of a storm drainage system designed to deal with flash flooding or something similar in my opinion. The gabions are probably serving dual purpose to add friction to the system slowing the water down as well as protecting soil from erosion.

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x-jla

I doubt they are stairs. That would not be a very safe stair to climb. Those cages can easily catch a foot and trip someone, and the rocks sometimes will shift especially if a river rock. Angular rip rap is slightly more stable, but still wouldn’t work.

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x-jla

Gabions are really only good for retaining walls, decorative walls...

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Wood Guy

Mighyaa, devil's advocate here--I've done several projects on piers; one's under construction right now. Not exactly keeping the outside out. And my house, built in 1820, has been sitting quietly on dry-laid stones for over 200 years now. It wouldn't take much to connect floor framing with gabion cages to keep things in place. Probably not well enough for a seismically active zone, though.

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natematt

You can weld to the cages, I think the bigger issue would be keeping the cages attached to the stones in a seismic zone....

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x-jla

I’d definitely mix the rock with a 1/4” minus gravel to fill the voids and stabilize them from shifting. You can kick those baskets and the rocks do move around. Typically, even to do a wood bench or something on top there are usually hidden steel posts that go through the wall into a footing.

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x-jla

The basket itself isn’t as important as the shape of the fill material. A dry stack stone wall has a lot of friction and surface area contact because the rocks are flat pieces of flagstone of slate. A gabion is usually filled with chunks of angular rock or rounded river rock. As you can imagine, they don’t have much surface are contact with each other.

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mightyaa

Woodguy... I've seen a cabin where the system is post and beam over cassions.  Then boulders and stone infill as the skirt; the beams and post were inboard and the floor cantilevered over this skirt.  Pretty cool since they started the base with big rocks, and transitioned to smaller diameter as it went up.  But it wasn't structural, just a aesthetic. It was however a newer structure and fully occupied/heated/utilities, not just the 'glamping' cabins below which are iron stoves, outhouse, and hauling in water. 

Historic barns I've done have been similar; pier, pile or real foundations under the timber posts and the stone is just infill to ensure the bottom of wall isn't buried or in contact with dirt.  Works well to limit wood rot, but mice, cold, weeds growing out of it, etc. are an issue; wouldn't use on a house.

I've seen historic dry stack; flat type stone.  Did similar once for a mountain cabin as a shallow foundation and support for the plank floors; but you need to have anchors, so you become grouted and call it a stone masonry foundation; you can reinforce like brick masonry.  Some newish ones are even sort of faked; think stone cavity wall where that cavity is wide enough to place the concrete and rebar (basically a dry stack veneer). I've seen timber foundations (log).. wouldn't do that; most rot out.

You can't weld to the gabions for an anchor anymore than you can weld to a chainlink fence and call it structural. Code is quite specific regardless of zone. The cages themselves are held together with bent metal clips and bailing wire which is slightly more robust than a ziptie :P. 

Maybe you might do it more like a double-wide and use hurricane anchors drilled into the earth and a self-supporting structure than just rest on the gabions to keep it off the dirt like a jack. But means and methods play a role; you'd have to have the anchors in place, set the basket and fill.. the couple times I used gabions, they are shipped as complete baskets filled with rock and lifted into place (bank stabilization stuff) from a flatbed trailer. They aren't filled on-site. Also, from what I was told when using them as bank stabilization... the cage in contact with soil might last 20 years before it fails (rust, corrosion). The system somewhat relies on silts and dirt infiltrating, condensing, etc. to hold together after the cage rots. Still though... What is the lifespan you are looking for?  

I've done cobble; the basket is redundant because the soil and grout you'll do ends up holding it together.  A adobe cabin I did used historic methods. Dig your trench, set up a board form (or use the trench bank), dump a layer of thick (3" grout), and press stones into it like giant aggregate... repeat until you are about a foot out of grade and transition to adobe bricks. Then parge the whole thing. Haybale is similar.  Earth floors are probably a pita with the EPA; I seem to remember the mud mix using oil as a binder. 

I should note I've never done these alternative systems with a permanent residence.  There are just to many 'cons' and failure points. All of them are homeowner constructed, remote where getting a concrete truck there isn't an option, and often a single or two room 'real cabin' accessed by a rough trail versus a 10,000 sf Aspen cabin. Or like the barn (which was existing and we were repairing); a accessory building that won't be occupied so mice, insects, heat loss, etc. aren't an issue.


Jan 12, 21 11:26 am  · 
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Wood Guy

Mightyaa, I know that typical gabion cages are flimsy, which is why my first comment was that to use them as foundations they would need a stronger cage.

The lead image here is a highish-performance addition I designed for my MIL: https://www.greenbuildingadvisor.com/article/all-about-helical-piles.

This is a Passive House on piers I was involved in designing and building: https://ecocor.us/portfolio/ash-point/.

I rarely do anything conventional; there is always a better way or something new to try. I've done a ton of remodeling over the years so I have a decent sense of what to watch out for. 

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