Prepare a firefighting pond for the construction site

ok. I am a structural engineer and would have serious concerns about backfilling a 5m deep hole with normal soil. The soil should be at least sandy or gravelly so that it can actually be compacted. But even I would be fully reliant on the [Bodengutachter]. Try to clarify the question of liability. I only know [Bodengutachter] who are excessively cautious.

Road embankments over several meters are sometimes deliberately built one meter higher (=loaded). Then you wait for the whole to settle. And then eventually you can assume that the settlements are largely finished...

No matter how you do it. For me, it would be too much effort, cost, and time-wise, and there remains a risk.

(The probably unsuitable soil you might get for free... but who transports it, which excavator works in a 5 m pond to compact it, etc... those are several tens of thousands)

Sorry for the off-topic, but it reminds me of a joking remark from an acquaintance. He has a weekend property with a shallow pond. The existing old weekend house is grandfathered in, but he is not allowed to build a new one. Jokingly, he then said that he would just put a 5x6m houseboat on the 6x7m pond.

Basement?

preferably 2 floors deep! :p

With 23m pond length, this is already the beginning of the access road to the underground garage beneath the cellar.

Basement?

There is a floating house from a basement company, of course with a basement. So it would definitely be worth considering ;)