Reinstall collapse in the ground?

So regarding hazardous materials, I would have fewer worries; what would bother me more is that during any digging work in the garden, after just 20cm there's already a layer of rubble. So if you, for example, plant a tree or some shrubs. And that's certainly not good for their root system either, although of course it depends on the amount and density of that stuff..

For the excavation under the driveway or terrace, it's probably not suitable, right?

Google search for LFU Bayern FAQ Aushub

Take your excavation. It cannot be more contaminated than what is already present.
However, there was once a discussion that soil excavation should no longer be used on the same property. That is off the table.

What you do with the construction debris is up to you to decide.
The worst value in both samples, with us, was chloride. Z1.2 classification.
Most was Z0.
The building materials from the 40s/50s are difficult to assess. They used whatever was available.
All companies had advised us against backfilling with the material, except those that offered a crusher.
What I cannot assess are the values. How are they to be interpreted? What kind of risk is being referred to?
Most debris is allowed to be backfilled in quarries or used as RC in road construction. It can’t be that toxic.

What would bother me is that after a spade’s depth you actually reach the debris.
As long as you only sow radishes, that might be okay.

Thank you all for your contributions
thanks for your link! And yes, regarding excavation backfilling I would also have no concerns: our soil analysis came out quite positive, no toxic traces were found.
I am still very uncertain about the rubble: on the one hand a minus for the reasons you mentioned (and the uncertainty whether it is really 100% safe?), on the other hand a plus due to about €3,000 savings (which however have the potential to affect our future garden life. Hm...)

Honestly, gone for 3000 euros Simply because the chunks keep bothering you Garage driveway, parking space yes, it can be included as a base. Doesn't bother

Would consider gravel for the terrace and driveway. Purchased gravel is nothing else. You can forget the panic mongers here.

If the area only needs to be filled up by 40cm, I wouldn’t put gravel in there. There is soil from the next new farmer for free anyway. 20cm on top, then topsoil comes anyway. Gravel doesn’t belong directly under the topsoil.

Who is panicking here? But there is something else. You are not obliged to fill [RC Material] under the terrace and driveway.