ᐅ Use of Earth Materials Z 1.1

Hello everyone,

The excavated soil at our site was classified as uncontaminated Z 1.1, containing 4 percent foreign materials.
I found out that it is allowed to be used as backfill in foundation pits.
I was advised against building our slab foundation or a terrace on top of it. But what about using it as filler around the house?

Is there any reason not to do so?

Let me tell you, I was so foolish and went ahead with it, and the end result was that the terrace settled, as well as the paved path from the entrance to the terrace.
After 3 years, I removed all the slabs on the terrace and realigned them. The paving after 6 years.

No matter how much you compact and tamp soil that has been loosened, it will never be compacted well enough to prevent rain from compressing it again.

Please use only mineral concrete.

This is my opinion and experience.

Endorphin schrieb:

But what about using it as backfill around the house?

If you can use the soil there, go ahead. But stick to the rules and don’t use it as a base layer for a terrace or similar. For that, use standard gravel, filled and compacted to a sufficient depth (your excavated soil won’t work for this).

Thank you for your reply. Why do you think my excavation cannot be compacted? Four percent of foreign materials (brick and concrete) is not much.

Endorphin schrieb:

Thank you for your reply. Why do you think my excavation cannot be compacted? Four percent of foreign materials (brick and concrete) is not much.

It’s not the 4% that’s the problem. The remaining 96% is what prevents you from properly compacting the excavation.

Try searching for "terrace base construction" or "driveway base preparation." You will then see how the proper base is built: not with soil, but with gravel.
It looks like this:

I hope this is not meant to be to scale. For a typical curb that a DIYer can still handle alone, with a height of 25cm (10 inches) and weighing about 34kg (75 lbs), a gravel layer of 10–15cm (4–6 inches) would be far too thin, and a crushed stone layer of the same thickness would be way too thick.

You should also aim to create a subbase that is at least somewhat frost-resistant. It doesn’t have to be 100cm (39 inches) deep for an extreme winter with four weeks at -25°C (-13°F). But I would still gravel down to a depth of 50–60cm (20–24 inches).

If you’re smart, you talk to the excavation contractor and have the areas intended for terraces, parking spaces, paths, etc., gravelled and compacted at the same time the foundation for the floor slab is being made. Compaction of larger surfaces requires skill or at least practice.

Soil cannot be compacted properly, and this also applies to crushed stone or gravel.