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Trenching through frozen ground w/ rigid insulation

Trenching through frozen ground w/ rigid insulation

Trenching through frozen ground w/ rigid insulation

Here is the scope of work:

Trenching through silty frozen ground with existing rigid polystyrene insulation about 2 feet down. Trench depth of 3.5 feet.
Laying in cables and then replacing the insulation damaged from trenching.
Backfilling with native soil.
Water necessitates doing the work in winter...water table is about 1' down.

Because of the length of the trench, I'm looking at the possibility of a trencher for cost savings. The problems with this is having torn up insulation. Anyone have experience with this? Will the insulation come out in manageable chunks or will it be a mess? Any way to filter/screen out the insulation from the excavation?

I also looked at the possibility of a dozer w/ ripper, but it won't work in this case. Excavators are slow...any other options or suggestions?

RE: Trenching through frozen ground w/ rigid insulation

Not sure I see a major issue. It will likely come out in small chunks and require some cleanup. You could consider three-sided "doghouse" insulation if you are concerned with properly replacing the existing insulation.

RE: Trenching through frozen ground w/ rigid insulation

How wide will the trench be? Frozen all the way to 3.5 feet? Look at using the trencher and expandable foam insulation and a foot of dirt.

Richard A. Cornelius, P.E.

RE: Trenching through frozen ground w/ rigid insulation

Don't do it on a windy day. Chunks of foam will go everywhere. If there are houses within 3 miles you will get complaints of foam in someone's swimming pool.
Most dumps charge extra for foam.
Once foam is broken up, only a team of healthy college students can round it up.
If you can expose the foam first, pour some molasses or something sticky on it to hold it together before breaking it up. We never found a good liquid for this.

(We once misplaced some foam used for low density fill below a roadway and had to dig it up).

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