Building ground - foundation recommendation

I can hardly imagine that a soil replacement up to 4.5m depth is that much cheaper. Then it would rather be the consideration of whether to build a basement in the groundwater. Certainly the most expensive solution, but in the end it has a basement and not gravel buried for 50k.

Goal lenses are also just annoying. They can actually occur in such a localized way. Everything around is great because of the sand, and right in the middle there was just a silted-up pond.
On the topic of pumping out water, recently has gained some experience.
Maybe he can help you or at least read through his thread...
https://www.hausbau-forum.de/threads/grundwasserabsenkung-laut-bodengutachten-eure-erfahrungen.43117/

Yep, as already mentioned, soil replacement is not economical due to the depth and water management. The peat must be removed or deep mixed.

The only foundation option in this case is unfortunately really piles.

I would get quotes from Keller Grundbau or Menard. They are somewhat cheaper. Menard has CNC columns. These are not precast concrete columns but are installed using the displacement method.
It is potentially a bit cheaper.

Unfortunately, everything is more expensive than a normal foundation.

The recommendation, of course, states that there should be a pile foundation. Therefore, I ask if you possibly know of any alternatives?

If there are alternatives, it is stated in the BGG.

or say, then you have to take care of it yourself up to and including the floor slab, which of course also has something to do with warranty.

Then there are none. So none for the entire DH. I wouldn't do that.

Very unfortunate if there is no alternative and 60 houses around didn't need a pile foundation - but okay :D

Even in the 90s there was already structural engineering. My parents also decided against pile foundation and opted for soil replacement because of the groundwater at one meter depth. That was in 1978. It already hit the finances back then.

Difficult situation, if I read that correctly you encountered peat and silt at several boreholes to a depth of 4.4m. That is really unfortunate but not uncommon for the Hamburg area (if I read that correctly). Without having seen the soil report, I can only tell you in general terms that an earth replacement considering the high (ground)water level is hardly economically feasible. You would have to lower the water column by 3.3m in fact. That is usually not done; instead, sheet piles are used and only a residual dewatering is operated. But the excavation pit for the multi-family house is correspondingly large and the sheet piles have to reach into the impermeable layer, otherwise a hydraulic failure of the ground is threatened. That is probably why the geologist named the pile foundation as the only option. An acquaintance had a similar situation. The house was placed on 16 concreted concrete rings (DN1000), which extend 2.5m deep into the ground. In her case, the groundwater was also 1m below ground level and an earth replacement would have cost around 70-80k with dewatering, excavation, disposal and backfilling for a small single-family house. They came to about 20k for the concreted rings. Dewatering would have made up the largest share of the 80k. Did the geologist have the structural plans of the house to create the report? I understand you are not building a basement?!