ᐅ Compacting a gravel layer of approximately 25 cm – experiences

Hello,

I have already searched online about the following topic but couldn’t find any information. Fortunately, I came across this forum.

Here is my question:

For a ground slab, one wants to compact a gravel layer of about 25cm (10 inches). Now, there is a compactor with a compaction force of about 8kN. This is definitely not enough to compact the entire gravel layer at once.

Would it be possible to compact the gravel every 5cm (2 inches)? Would this achieve the same result?

That means applying 5cm (2 inches) of gravel, compacting it with 8kN, then applying another 5cm (2 inches) of gravel and compacting again. Repeating this effectively three more times.

Thank you very much!

Robert

Your geotechnical engineer should specify how much the ground needs to be compacted.

How the contractor achieves this is something they should know as professionals. One method might be the one you describe. Whether this is sufficient, I don’t know. However, depending on the layer thickness, doing it every 5cm (2 inches) can be quite tedious.

In any case, a proper, passed compaction test should be conducted at the very end.

Hello

This is not my area of expertise,
but eight kN is rather lightweight.

For our foundation slab, I used something in the range of 70 to 90 kN.

Of course, this also depends on the material used.

Olli

Theoretically, yes.
But in practice, who wants to take on that work?
Definitely perform plate load tests.

I would recommend a proper vibrating plate with 50 to 70 kN.

I didn’t even know there were still such toy plates.

Hello,

Thank you for your responses!

The compactor is said to compact 20cm (8 inches) of soil. I’m rather skeptical about that. Since it will be available anyway, I would compact a 25cm (10 inches) layer of gravel in 4-5 passes... No house will be built on the slab. The foundations are already in place, and the slab will be installed as a floating slab. This means inserting a barrier between the slab to be poured and the existing foundations.

Thanks and good luck from Leipzig!

Robert

Practically no
Theoretically no
When installing gravel, the layer to be compacted should be at least three times the thickness of the largest particle size. This allows the gravel to settle evenly and the fractured particles to interlock. For example, gravel sized 0-45mm (0-1.8 inches) should be laid and compacted in layers at least 15cm (6 inches) thick. Compaction should not be done with a "smoothing iron" but with a heavy vibrating plate compactor of 55 kN or more. The soil report should ideally include installation recommendations, which was the case for us. In any case, perform a plate load test at the end, but no earlier than one week after installation. This allows the material to "settle" after compaction vibrations, otherwise the results may be inaccurate.