Filling construction pits - what is the best way?

Hello hello,
our house construction is still at the beginning, but perhaps in the most difficult phase: the excavation pit. Don't laugh, we have already had quite a lot of fun with it.
Our plot is located in the "Munich gravel plain" and the basement will be partially submerged in groundwater - at least to some extent. Since our construction company is already struggling quite a bit with this issue in advance, it would be really helpful if we knew a little more...
I have attached a drawing to make it perhaps a bit easier to understand.
Viewed from above, the layers are as follows:
1. Topsoil = humus
2. Gravel layer (gravel sands with stones and silts according to the report)
3. Glacial till

The slab will be in the till layer, which will be almost waterproof (at least the deeper you go). The gravel layer carries groundwater.

A clean layer of gravel will be formed under the slab - water will then stand permanently here later on.
Now the question - what is the best way to build up the backfill??

Using gravel would be best for compaction, but it leads to water standing permanently at the transitions between the slab and basement walls, since more water will flow from the groundwater-carrying gravel layer here than the till - if at all (I don’t expect it to) - lets drain away. Theoretically, a waterproof shell should be able to handle that, BUT....

Or should the layers be rebuilt according to the neighboring layers?
Or would you even go further and build completely with glacial till (as far as the excavation allows) in order to possibly have as little water as possible standing by the building - and accept the disadvantage of poor compaction?

It would be great if someone has experience with this.

Best regards, Schicolina

Hello,

Since our construction company is already quite lost with the issue in advance, it would be good now if we were a bit more knowledgeable....

Why is your builder "lost"? All necessary measures are outlined in the soil report; he should surely be able to read it

It would be great if someone had experience with this.

I hope that no one answers this topic; the answer belongs in expert hands and any – no matter how well-intentioned – advice is on the one hand not transferable to your situation and can cost you a lot of money in case of doubt!

The soil geologist (soil report) will surely be happy to answer all your questions if your builder does not see himself capable of doing so.

Kind regards

Hello construction expert, thank you for your response. My question somehow combines two issues, one of which the soil expert will probably not answer: is it better to constantly have water pressing against the white tank, or do you try to prevent this by all means possible, even if that means accepting settlements? But maybe the components of the gravel marl also attack the concrete – so direct contact might not be good, or maybe it’s something completely different....

Of course, we will follow up here again, but a second expert opinion wouldn’t have hurt. By the way, I would also have appreciated reports from homeowners (has compaction according to the soil layers even happened before?), how one then "deals with" it everyone has to decide for themselves – that’s probably true, but not only with construction topics.

The statement from the soil expert is: The water-sensitive clay soils reached during excavation are suitable for backfilling / re-filling; however, in the softened state they are poorly suitable for installation and compaction.

I’m curious if he will be more specific upon inquiry – in my experience with geologists rather not – or it will get expensive...

Best regards, Schicolina