Hi,

I am planning to insulate & back fill a meteor crater like cavity along with a rectangular cavity on my back yard with EPS foam to be used as a base for a 32×16 above ground pool.

I recently found that a specific type of EPS, Geofoam, is used as cavity fills but not entirely sure about whether it is too much different than to its roof EPS sibling – given if they have same density. For example Geofoam 12 seems to me very similar to Type I roof EPS when it comes to compressive strength it has. Only difference I can see that while compressive strength of Geofoam version is published at 10%, 5% and 1% deformation rates, roof version usually is published only for 10%.

So, I already calculated approximate pressure to be ~1.8psi for the pool (~4ft *0.433 psi for 1 pcf of water + some overhead) and compressive strength even for Type I EPS seems to be 2+ psi already even when 1% deformation rate. 

The cavities I need to fill are:
– ~17 ft wide 2ft deep in the center sphere cap
– 15×16 ft rectangular cavity that is 4-6″ deep.

For the first one, I will make a level section on the center with gravel and put the first block on top of it. Then start adding other blocks in a staggered fashion to outwards. And any irregular cavities below the boards will be filled with secure set spray foam that is rated for lifting slabs etc or granular fill like crushed stone and/or sand.

So the questions are…
– Would I have any concerns using roof type EPS as back fill aside from structural concerns?
– Any structural concerns?
– Any other concerns  🙂 ?

I have ~43 pieces of 4″ 4×8 Cellofoam boards that I retrieved at a very good price that seems to be more than enough and I don’t want to back fill the area with soil as I might upgrade my pool later and take out some of the EPS on that crater section to have a deep end – but that’s a different adventure I would like to do later on 😉