Compact gravel layer of about 25 cm - Experiences

Hello,

I have already searched the internet regarding the following topic, but found nothing. Fortunately, I came across this forum.

The following question:

One wants to compact a gravel layer of about 25cm for a concrete slab. Now, there is a compactor with a compaction pressure of about 8kN. This is definitely not enough to compact the gravel all at once.

Would it be possible to compact the gravel every 5cm? Would this result in the same outcome?

That is, apply 5cm of gravel - compact with 8kN - then apply another 5cm of gravel and compact with 8kN. Repeat this effectively three more times.

Thank you very much!

Robert

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

How the contractor achieves this, he should actually know as a professional. One possibility can be that it is done as you describe. Whether that is sufficient, I do not know. But depending on the thickness of the layer, it is quite tedious every 5 cm.

In any case, a corresponding, passed pressure test should be carried out at the very end.

Moin Moin

It is not my area of expertise
but eight kN is rather a toy

with our base slab I had something around 70 - 90 kN in use.

That certainly also depends on the material used.



Olli

Theoretically yes Practically who wants to put themselves through the work Definitely conduct plate load tests I would take a reasonable vibrating plate with 50 to 70 kN. Didn't even know there are still such toy plates.

Hello,

Thank you for your answers!

The compactor is supposed to compact 20cm of soil. I rather don’t believe that. Since it is there anyway, I would compact a 25cm gravel layer in 4-5 layers... There is also no house to be built on the floor slab. The foundations are already there and the floor slab is to be laid floating. That means inserting a barrier between the floor slab to be poured and the existing foundations.

Thanks and best regards from Leipzig!

Robert

Practically no
Theoretically no
When installing gravel, the layer to be compacted must be at least 3 times as thick as the largest grain of the material. This allows the gravel to settle evenly and the angular grains to interlock with each other. That means gravel 0-45 mm should be installed and compacted in layers of at least 15 cm. And not with an "iron," but with a heavy vibrating plate of 55 kN and larger. A construction recommendation should actually be included in the soil report, at least that was the case for us. In the end, definitely perform a plate load test, but no earlier than one week after installation. This allows the material to "settle" after the vibration, otherwise the result will be distorted.