Use of GeoFoam material with backfill in AGP partial bury

[hotchalupa]

Hello everyone!

My semi in-ground AGP build is underway. The pool is 32x16 oval, and the excavated perimeter around the pool extends laterally, on average, about 2 feet from the pool wall, and is anywhere from about 24" to 34" deep (more than 60% is at around 34" of depth). That is a lot of void to backfill, especially if using a slurry mix, as required by the mfg (Doughboy).

I've been researching GeoFoam (EPS) as a way to augment the process, as well as provide much reduced lateral pressure. The idea would be to use GeoFoam to occupy the majority of the 2 feet wide by 3 feet deep void, allowing for about 12 inches or so of backfill at the top (plus any backfill around and in between the material and the pool walls).

Has anyone researched or ventured down this same path? Any thoughts, tips, comments...concerns?

Thanks!

Sneak peek...

View attachment 69826

 

[duraleigh]

I am not sure what geofoam is but I assume it is somewhat compressible. I don't see how it would reduce any pressures.....I would believe the best backfill would be #57 rock.....it's clean rock about 3/4" size on average and will not compact (or move)

 

[hotchalupa]

I am not sure what geofoam is but I assume it is somewhat compressible. I don't see how it would reduce any pressures.....I would believe the best backfill would be #57 rock.....it's clean rock about 3/4" size on average and will not compact (or move)

Being foam based, it does sound like something that would be weaker... But, for context, here is some technical data on geofoam, including its compressive resistance:

Geofoam: Technical Library

The way it achieves reduction of lateral pressure is by assuming the majority of the volume in the void, in a stable manner. There are different densities available, depending on the application. According to the manufacturer, it weighs somewhere around 1 to 2 percent what soil weighs. It is used in public works projects around the states. I just don't know of anyone who has used it in residential applications (I'm sure it has, but I don't know anyone personally).

Backfilling an AGP pool that is partially buried requires stable backfill that packs well (as opposed to rock, which does not). The problem comes from the walls having no inward support, and only holding the backfill in place via the pressure of the water while filled. When drained, any non-packed backfill material can exert enough pressure to collapse the walls. Your recommendation would work great for backfilling a concrete pool, since the pool walls are self-supporting.

My goal is to reduce the volume of the void without the need to fill its entirety with slurry cement mix. I am hoping to hear from anyone who has used GeoFoam in a similar application.

 

[BigEinAZ]

You'd still have to pour grout in the voids and you'd probably end up floating the blocks. You could use CLSM (Controlled Low Strength Material) and pour it in lifts, allowing a days cure in between pours. Once it sets, it won't be imposing much of a surcharge on your walls.

 

[duraleigh]

I understand what you are saying about lateral pressure. You could get an engineer to calculate it for you but with #57 rock, the load is almost all down, not laterally. Additionally, you could backfill in layers (lifts) and bring the pool water height up with it and there will be NO lateral pressure at all.

#57 rock requires NO compaction (in fact, it won't compact) but is a perfect backfill if you are planning on concrete surface over the top of it. Compressible material is simply not acceptable as a substrate for concrete. If you are doing pavers or a wood deck above it, then compressible materials are fine.

 

[hotchalupa]

I understand what you are saying about lateral pressure. You could get an engineer to calculate it for you but with #57 rock, the load is almost all down, not laterally. Additionally, you could backfill in layers (lifts) and bring the pool water height up with it and there will be NO lateral pressure at all.

#57 rock requires NO compaction (in fact, it won't compact) but is a perfect backfill if you are planning on concrete surface over the top of it. Compressible material is simply not acceptable as a substrate for concrete. If you are doing pavers or a wood deck above it, then compressible materials are fine.

Your bring a great point... I am looking at all options at the moment. It'll be some time before I do the backfill. I will definitely update this thread if I end up going with EPS/geofoam, if anything for posterity.

Thanks for chiming in!