Earthen Walls

In a couple years I'll be back home and likely ready to work long-term with my preffered company. Once I'm there, I'm likely going to start experimenting with small-scale Earth Berm structures. I want to maybe used mechanically stabilized earth in the walls to reduce inward pressure and increase stability. My question would be how thick would a wall made of sand need to be in order to make it "worth it" in regards to thermal mass. Or should I just make the dirt slope up to the roof line?
I really like Mike Oehler's designs, but I don't want to go fully underground. I want the look that wattle and daub or cob provides. Or a planted slope reaching up to the roofline.
I'll post a later comment with a couple sketches of what I have in mind.

I've lived in earth bermed houses for a couple of decades, and was involved with the discussions and decisions about building. We always made any retaining wall or underground wall of stone, and then built earthen walls only above ground. We are in high desert without precipitation that soaks the ground appreciably, and we were building on a sandy low slope with no groundwater. But still, all underground walls had to be stone.

I don't know what you mean by mechanically stabilized earth. Around here, stabilized earth means about 5% cement. I wouldn't use it for underground retaining walls. I'd use either proper concrete, or stone masonry. Where I live stone masonry labor is affordable, and there must be other materials too, but I haven't seen them in person.

Earth moves and settles over the years. Earth is heavy. Ground tends to be damp, and insufficiently stabilized earthen structures crumble in damp conditions. Even where the ground is dry, like where I live, earth bermed walls are cool in summer so they collect condensation. Earthen walls have great properties of adsorbing humidity (I forget the proper term) so, for example, our earth plaster and lime wash on the interior (room-facing) surface of the bermed walls would tend to peel itself off slightly over the years.

You might want to look onto the Wofati. It is built at ground level, with earth roof and bermed on all sides.

Rebecca Norman wrote:I don't know what you mean by mechanically stabilized earth. Around here, stabilized earth means about 5% cement. I wouldn't use it for underground retaining walls. I'd use either proper concrete, or stone masonry. Where I live stone masonry labor is affordable, and there must be other materials too, but I haven't seen them in person.

MSE is basically adding horizontal layers of some sort of stabilizing material, such as fabric, every few inches or feet. This immensely reduces side-load and lateral shifting of whatever medium you are using. it is commonly used in the building of raised roads and retaining walls. There's a very informative video here,  
Also, I don't really want an earthen roof. This would be above ground with sand piled up against the walls. I'm thinking adding some sort of fabric--maybe strips of screen material--every 4-6 inches will reduce load on the walls. Ever since I read about Mike's PSP system in his book, I've wanted to try to adapt it to my own desires.

Ben Taylor wrote:There's a very informative video here,

Thanks for posting that video. It opens up a new world of possibilities for me to accomplish things that I thought may not be possible.

Michael Helmersson wrote:

Ben Taylor wrote:There's a very informative video here,

Thanks for posting that video. It opens up a new world of possibilities for me to accomplish things that I thought may not be possible.

No problem. I hope something interesting comes of it. I was thinking a good assessment of the possibilities is to make a tightly layered wall segment. See how thin of a facing you can get away with, since it's mostly there to prevent erosion. Though I'm not convinced it is worth doing before the surface.

Ben, that is a great video and as a Civil Engineer I learned a lot from it.
I have not used that material system .
Even though he demonstrated its use with cups, I wonder if there is a minimum size structure where it works effectively?

I will ask around.

I found this video which details more practical uses of the use of Mechanical Stabilised earth with a variety of examples.

I would be careful with your use of this system.
The “mechanical stabilization” resolves   lateral sheer forces into vertical forces that don’t push the sand in your wall apart.
The earth surrounding your house has not been mechanically stabilized so it will push inward on your walls. Your walls will have very little resistance to this lateral force and will cave in.
If you hope to succeed with a system like this,  the earth in the area surrounding your house will also need to be mechanically stabilized. Perhaps it could be removed and replaced in layers with the mechanical stabilization extending out into the surrounding area. How far this will need to happen will depend on the angle of repose of surrounding soils.
For x ample with a one story house, you MIGHT need to remove 15 feet of dirt to the level of your floor and replace it in compacted 1 foot layers with sheer fabric between each layer. I made that up, but if sandy, perhaps more; if hard dirt, perhaps less. If fairly solid rock, perhaps not much at all.
Also, realize that the wall will have to retain or devote any water that passes through the soil.

charley price wrote:I would be careful with your use of this system.
The “mechanical stabilization” resolves   lateral sheer forces into vertical forces that don’t push the sand in your wall apart.
The earth surrounding your house has not been mechanically stabilized so it will push inward on your walls. Your walls will have very little resistance to this lateral force and will cave in.

Your correct, Charley. The idea bouncing around in my head has evolved into an above-ground structure with either very thick vertical walls filled with MSE and facades inside and out. Or MSE sloped up against the wall. Though, the sloped option seems to be a dubious prospect due to rain run-off perhaps damaging it over time. The enclosed wall seems more likely to stay dry and easier to be built to whatever code might apply.
If things go well, I'll be moving back home next year and will be able to build a shed using this idea as a proof of concept.
I suspect the wall would need to be probably two feet thick to provide notable insulation/thermal mass akin to an earth bag system. But that's based on an uneducated guess.