Does anyone know of a source for finding out what the load bearing strength for an earth wall would be if built with the optimum proportions of sand and clay and allowed to dry thoroughly?
I'm trying to figure out if I could build a WOFATI (earth sheltered with living roof and large umbrella) style home with earthbag walls without needing additional post and beam support for the heavy roof. We'd like to build the horseshoe shaped walls like is done with earthships and realize that we may need to include some buttressing on the straighter sections to give the walls more stability to hold up the earth bearming on the sides.
The builing would be in a zone 6 area with about 23 inches of rainfall spread out across the year. They do get a couple of feet of snow standing on the roofs in the winter as well. Because of having the living roof, I would be looking at a shed style roof with not too steep of pitch.
South facing with an attached greenhouse for solar gain and RMH inside home for supplemental winter heating. Air tunnel venting through the earth mass for fresh air.
Does anyone know of someone who has these types of calculations?
I don't know how do these type of calculations but I can tell you from construction experience. There are a couple of things you can do. Get a little bit of your dirt wet enough it can manipulated. Start rolling it into a half inch cylandier. If you get past four inches before it falls apart you don't need to worry about cave in.
I think with earthbags. I wouldn't worry about compressive strength at all. It's not bricks but pretty much the same deal. I would be more worried about the surrounding Earth not moving around if it gets saturated. Put a little slope on your walls and use the weight of the bags and roof to help hold the fort back.
I'm going to try to build one with out any wall support except for railroad ties to build the roof on top of. But I know my soul is loess going to hard clay.
You might try going to your county extension office and find your grid coordinates soil type.
posted 3 months ago
Thanks for your thoughts Zach.
I totally understand the concerns about earthbag walls getting wet which is where I was thinking that using the large umbrella of the WOFATI would be a really good adjunct to them.
Good to know that the dried walls can be so sturdy though.
I'd be really interested to hear how your project turns out as well. What size of structure are you thinking of and are you looking at a circular building?
Earthbags could work, but will be stronger if the walls are curved out a bit. Check out MyLittleHomestead on Youtube to see their earthbag buildings, one of them has a lower level below grade but it is a circle so it will have great strength due to that. Tying in several deadman for straighter walls will complicate the waterproofing unless you plan to leave out the plastic sheeting against the walls and stick to only the umbrella, which I wouldn't recommend.
Wooden posts say every 8-10 feet with earth bags as filler, with a bit or arc bowing out towards the surrounding earth should resist the soil pressure and still allow you to place sheeting along the outside for water protection. I'm not an engineer though, so overbuild if you don't hire one to calculate loads for you. Saturated soil plus snow load, plus the weight of you or whatever might walk on the roof can add up!