Where is Bob when we need him? Hahaha.
I am not trained carpenter like Bob is, but I have worked for mechanical engineers and builders several years of my life, but mostly as "grunt labor". Don't take any numbers that I say here as gospel, just as ideas to check out.
From memory I think engineers don't expect 2x6 decking to span more than 2 feet without having some deflection. Again from memory, don't hold me to this, but I think that was allowing for 40 or 50 psf (pounds per square foot).
There is a calculation for live weight + dead weight to give a design criteria. I think live weight is, for example you and some friends, and dead weight would be your clay/dirt floor + furniture, etc. Obviously I don't remember it all, but commercial has a heavier design criteria than residential.
Also, I don't really know what a 3,000 lb. floor really means. Do you mean over the area (about 450 square feet) of your 24' yurt? It couldn't be per square foot, but over what area might help you discover the "psf" of the finished product. But weight (wait) there is more.
When your floor is being "poured", it is going to be full of water, so it will be much heavier for the first few weeks until it has dried out, before you start putting your linseed oil on top. My question is, do you need to design for that weight? There is some safety factor designed in, but I am not sure if the designed in safety factor could cover this or not.
Also, if you haven't already thought of this, and if you are living in a cold area you might consider designing distribution tubes for hot water
embedded beneath the surface of your floor, and designing
under your floor, and insulating around the edges.
Whatever your design, I think it has to be for close-to-zero deflection, otherwise if the floor bends at all, deflection will break, or at least crack your floor again and again until it is unusable. Clay/dirt floors are not like concrete, they have no structural integrity, no stiffness.
I have not built an above ground clay/dirt floor, but I was at a party where we built a ground-crete floor, maybe 25 years ago (in the 80's), but I was never back to see how the floor survived over time. I think it is a very cool idea. I wish I had answers instead of just questions.
I wish you the best of luck on your project.
Rod
rod
yurtlocker.com