Sand sucks for trenches

Frequent readers will know this has been the week of digging trenches for footings. I am completely convinced that code is ridiculously pessimistic when defining footing requirements. Our footings will be awesome and something on the order of 100 X what we probably really need.

But that is not today's topic. Turns out the North side of our lot (to the right as you look from the front) is built directly into "A" Mountain. The footings trenches have been a struggle every inch of the way. In geologic time frames these footing will not move. Any. The South side, the side we share with DnT is a whole other story. The old car port may as well have been at the beach. Nothing but sand, and a few enormous round boulders.

Beach sand would actually have been an improvement. Beach sand is quite angular so it kind of hangs on adjacent pieces and can be compacted quite nicely if contained. Now, our sand is what I now know is "river run" sand. Nice and round. Won't hang on any damn thing. If you know anything about angle of repose, I'm pretty sure the angle of repose of river run sand is asymptotically close to 0.

This stuff is like water. You can't compress water at all in a cylinder or some enclosed space. No enclosure, the water runs all over the place and puts up no resistance at all. That is the way this river run sand works. And we have an infinite supply of it. We have the worlds supply of "A" Mountain rock and river run sand.

So, we had us an emergency all-hands confab with the execs at the concrete company, CtC, and a Block Mason. We considered the option of:

  • Building a wall around the sand to contain it.
  • Replacing the sand with good fill.
  • Mixing the sand with good fill and using a beefed up forming system to support the retaining wall part of the garage slab while it is poured.

We went with plan C. They mixed and compacted and mixed and compacted. Added water. Compacted some more. We'll see tomorrow how it works. All we really need is an angle of repose closer to gravel and we'll pour the slab and retaining wall to be thicker than planned, but will be structurally fine.