The strip foundation has developed a crack

I thought about putting in gravel, tamping it down properly, hydro-isolation, reinforcement steel and concrete on top of the entire foundation, so that it lies 15 cm higher again.

But this only results in a 15 cm layer of concrete that has no structural connection to the rest of the strip foundation. At what distance are the stirrups laid? Or have you laid bent mats as a cage? You should glue your new longitudinal reinforcement downwards into the existing foundation with stirrups. I would even do it at the same spacing as the already installed stirrups, just shifted by 10 cm and glued in about 50 cm by feel. What does the structural analysis say about the reinforcement? How large is the concrete cover? Could it possibly be too small?

I suspect your crack comes from compaction. Compacted soil downward inside and pushed upwards again under the foundation.

No one here knows statics, I already looked for someone but found nothing.

Rebar cage 10mm spacing 30cm, therefore 18mm reinforcements in 3x2 rows.

The compaction could even be right, I have already thought about that.

I can also increase the height of the base plate to 30cm and even higher.

I thought about drilling into the strip foundation from above at intervals of 20 cm, moving the drill so that larger holes form inside the foundation, inserting anchors and cementing them, when the cement hardens then pouring the base plate above it.

The new reinforcement then comes in the format 20x20cm.

Hi,

I stopped by a construction site where 17-story apartment buildings are being built and had a conversation with the site manager there.

He looked at it two days later and said I can ignore it, the load on the foundation is not significant.

I have now compacted the topsoil as best as possible with the wacker plate compactor, then I filled about 10cm of a gravel-sand mixture up to the edge, which I leveled with a large vibrating plate.

I drilled the strip foundation vertically every 30cm and installed anchor hooks, through which I pushed 10mm thick reinforcement.

Hydro isolation is also applied, reinforcement 20cmx20cm.

Thickness of the concrete slab 20cm.

Now I'm waiting for the rainy days to pass, and then 26 cubic meters of concrete will be ordered.

but I first had 200 cubic meters of soil delivered and raised the plot.

Now I have raised it, so it should no longer freeze.

No, the soil that lies inside I had delivered, it is still settling.

I have now compacted the topsoil as well as possible with the wacker plate, then I filled up about 10 cm of a gravel-sand mixture up to the edge, which I leveled again with a large vibrating plate.

Sorry, to me it reads like proper shoddy workmanship. The first thing I learned during our house construction is the difference between soil and sand/gravel and the phenomenon that the structure of soil/topsoil holds moisture, while sand lets moisture pass through. Therefore, I would not build residential houses directly on topsoil.

Hi,
Why is that, I’m not building directly on the topsoil, the strip foundation supports the concrete slab and underneath the slab there is gravel with [xps plates].

It is more of a concrete ceiling that is supported from the middle.

In total, there is 130cm of concrete on the facades.

The crack did not occur because of frost either, the concrete settled poorly at that spot, I noticed this when I was preparing the connection with the hammer drill.

After about 4 - 5 cm the drill just went right through.

And how do you now ensure that the self-created aerated concrete has not appeared in several places and that the building can stand on it without any problems?

Why is that, I am not building directly on the topsoil, the strip foundation holds the floor slab and beneath the floor slab there is gravel with XPS boards.

However, one can definitely get that impression when trying to organize your words and pictures.
On the first page one can see a kind of strip foundation, surrounded on all sides by topsoil. Step 1 would have been to remove this at least within the building site.
The subsequent floor slab, despite XPS and whatever else is underneath, must not bear on the topsoil, which must (again) be removed.