What happens to polystyrene directly in the soil over time?

[JockeHX]

As the title says, what happens to foam plastic that is directly in the soil over time? I've built a retaining wall that needs to be backfilled but underestimated how much soil was needed.

If the foam plastic retains its shape despite constant moisture/water/frost, maybe I can fill it with some EPS I have lying around?

 

[Isakare]

Dug on my property between the garage and the house to lay a cable, and there's polystyrene in the ground along the slab, not sure why. But anyway, nothing had happened to the polystyrene that was placed in the ground 28 years ago.

 

[JockeHX]

Dug on my property between the garage and house to lay a cable, and there is styrofoam in the ground along the slab, not sure why. But in any case, nothing had happened to the styrofoam that was put in the ground 28 years ago.

Sounds positive! And was it lying directly in the soil without any draining material?

 

[Lostmoose]

Dug on my plot between the garage and house to lay a cable, and there is Styrofoam in the ground along the slab, don't know why.
But anyway, nothing had happened to the Styrofoam that was put in the ground 28 years ago.

It's probably the edge insulation you've found. Styrofoam is placed like that so that the frost doesn't find its way under the slab.

 

[Isakare]

Sounds positive! And it was placed directly in the ground without draining material?

Gravel type 10 cm closest to the slab, but the boards extended 60 out, and the rest was just in soil. The boards are laid tilted outward, about 45 degrees, so at the farthest point there was probably 50 cm of soil over.

 

[Isakare]

It is probably the edge insulation you have found. Styrofoam is placed like that so the frost cannot penetrate under the slab.

That's probably correct, then there was no insulation at the edge.

 

[JockeHX]

Single type 10 cm closest to the slab, but the boards went 60 out, and the rest was just in soil. The boards are laid sloping outwards, about 45 degrees, so at the furthest point there was probably 50 cm of soil over.

Great. Now I feel like I can fill in with some foam plastic with a clear conscience

 

[Isakare]

Great. Now I feel that I can in good conscience fill it out with some cellplast

A stretch of road was constructed here where I live, it's a fairly steep hill where heavy trucks transport stone from the Stockholm bypass. The entire embankment was built with polystyrene, and we're talking layers of several meters, which were then filled with macadam and paved.