Last plate pressure tests repeatedly fail

Could be, but it doesn't seem logical to me. Because with RC gravel, subbases for roads for 40t are built (yes, smaller weight than a house but concentrated on a much smaller area). So in my opinion, either the ground is so poor that you need a deeper gravel bed or there is something wrong with the gravel (as someone already said further above).

Basically, the RC gravel must be approved in the area by the lower water authority if it is a "affected area". Additionally, of course, this must be coordinated with the structural engineer, as they ultimately calculate and must use appropriate values that can differ significantly for RC and KS (etc.) gravel. Then the earthworks or concrete contractor must also be on board, not everyone works with every material. RC gravel usually also has an approval, but I have seen RC gravel "ranging from… to". Sometimes with a lot of debris (organic matter, plastic, etc.) or clean. Next door to us, someone built exclusively with RC gravel, and that is one of the most expensive designer cabins in the construction area (Nelskamp solar roof tiles!, "designer" garden cabin, and much more). However, if no further feedback comes from the OP, there is no need to say much more about it here. From the initial text, I may have also read that the OP did the trade themselves (without coordination with the other trades?).

Hello,

Under certain conditions, RC material is suitable for use as a base layer material. Personally, I find RC material quite good. I will simply list a few points that need to be considered.

- Grain size distribution must be suitable (but this applies to all materials)
- Often RC material is not suitable as frost protection (this is not relevant with a 40 cm structure anyway, as either a basement or frost skirts are planned)
- Possibly requires approval, because due to the components, the LAGA class Z1.1 or Z1.2 applies. For example, Z 1.2 may only be used in hydrologically favorable areas (clayey soil layers and a groundwater distance of > 2 m). Since there is rock here, this should not be a problem.

As already mentioned, the material should be sufficiently watered during installation. But the water must not remain standing in the cushion.

In general, the values do not look bad. Consistently an EV2 of >100 MN is more than sufficient. The question is what was required – 80 MN/m² is common for a single-family house.

The EV2/EV1 value indicates the ratio of the two loads from the plate load test. EV1 is the first load and EV2 the second load. The soil is stressed and compacts the cushion by the stamp, then unloaded and the stamp lifts slightly. Then the second load is applied. The value thus indicates how well the material was compacted and whether there is theoretically still room for improvement.

Now to the problem: My personal opinion: This will hold... 40 cm and then comes the rock. Where should harmful settlements occur? Actually, the cushion only serves as a cleanliness layer... (of course also depending on how the rock looks, whether it is actually rock at all... I have seen earthworks calling something rock when I could push the Kunzel rod in by hand).

But unfortunately, it is about the warranty in the case of damages... whatever causes them.

So, what could the problem be... actually, as the previous speaker said, too little buildup (the plate load test penetrates about 60 cm into the subsoil) and measures the "rock" too. Wrong grain size distribution (values are good, compaction not good). Not well compacted (for whatever reasons... wrong equipment, wrong operation, too little water, too much water).

I would call the soil surveyor and ask for his opinion. He recommended the structure and knows the subsoil.

Best regards

First of all, thank you to everyone.

meaningful pictures of the RC gravel (close-up, overall, high resolution)

Photo is attached
The soil surveyor was here today and said that our installed RC gravel has a very high sand content. He suspects it's too high. He took a bucket full with him and is analyzing it. Feedback is still pending.
The specifications for 40cm RC gravel, installed and compacted in two layers, come from the soil surveyor.

Does the vibrating plate "float" while compacting on the ground?

I don’t quite understand what you mean by that?!

The question is what was required, 80 MN/m² is common for a single-family house.

Yes, the 80 MN/m² is required, as well as the value of <2.5 EV2/EV1.

But unfortunately, it is about the warranty in case of occurring damage... whatever causes it.

Yes, understandably, the shell builder will not start for warranty reasons as long as the values are not met by the contractor.

So, what could the problem be...
Wrong grain size distribution (values are good, compaction is not).

Grain size distribution 0-32mm, as already mentioned above with too high sand content?

wrong equipment, wrong operation, too little water, too much water)

The vibrating plate is a Wacker DPU weighing about 550kg. The civil engineer thinks that is completely sufficient.
This week they even went over it again with a 1.2-ton roller as a precaution. Without success...

What is too little or too much water? Both layers were watered and compacted. Possibly with too little water. Unfortunately, it has not rained at all in the last two weeks, and hardly before that either.

I would call the soil surveyor and ask for his opinion. He recommended the setup and knows the subsoil.

Yes, his response is still pending.

In the picture, I noticed the proportion of brick. Brick behaves comparatively elastically and "springs," which loosens the cushion again. The same could happen with the "rock." What kind of rock is there? If the sand fraction is too large, a smaller device with a smaller surface area should be used. Actually, the "worst" thing that can happen in this case (assuming real rock) is that the building settles evenly by 0.3 to 0.5 cm. The values are the same everywhere. Such settlements are actually no problem for a single-family house (with clay soils, settlements of up to 2 cm are standard). Is the foundation carried out via a slab or are strip foundations still being "dug"?

Thanks for the info. I have attached a photo. The rock on the right is clearly visible. Further back, the rock is more brittle and "fragmented." Founded with WU slab without strip foundations.