Interpretation of the soil survey report

I read it exactly the other way around. The clay is supposed to remain. Therefore, only about 0.5 m excavation. And then about 1.5 m build-up on top.

Yes, I had already received the following feedback from the soil expert: "Of course, you can also remove the clay layer and then build a frost-proof and water-permeable sand-gravel mixture below the foundation with the support on the glaciofluvial sand. But that also costs money and will significantly increase the costs regarding the earthworks."

and are currently obtaining offers for the upcoming earthworks.

Why doesn't the general contractor do that? Earthworks are included in the scope of work description at, for example, 30cm depth (at least that is common). It makes no sense to have two earthwork contractors working. The general contractor is also the contact person for reading the report.

Why doesn’t the general contractor (GC) do that? Earthworks are included in the construction description at a depth of, for example, 30 cm (this is usually the case). It makes no sense to have two earthworkers working.
The GC is also the contact person for reading the report.

The GC will offer the service if needed but has already stated that he cannot make the most competitive offer and that we should preferably approach a separate earthworker.
On Thursday, I have an on-site appointment with a civil engineer and want to make sure that I am prepared and ask the right questions. Accordingly, your contributions are very helpful to me.

I now understand the overall situation as follows: due to the significantly deeper position of the floor slab (compared to the assumption in the soil report), it might make sense to remove the entire glacial loam layer in order to forgo drainage accordingly. I am curious whether the civil engineer will have a similar opinion on Thursday.

So, the soil doesn't look too bad at first. Have there been any dynamic probing tests conducted? From the documents, I gather that strip foundations are planned?

I'll give a brief assessment and what I would have written...

Since there are silt components in the sandy soil up to 1.5 m below the [GOK], this is not frost-resistant. The geotechnical engineer should have specified the frost action zone and the frost-proof foundation depth in their report.

Frost protection can be ensured by:
1. A frost-proof structure. This means excavation and installation of F1 material up to 1.0 m below [GOK] (1 m is only assumed, [GOK] is the new planned ground surface level).
2. Frost skirts up to 1.0 m below [GOK] (then non-frost-resistant but still well-compacted material can be used).
3. Strip foundations up to 1.0 m below [GOK].

Building waterproofing:
Here, either a perimeter drain with damp-proofing against soil moisture or a waterproof concrete slab against pressurized water is recommended. Since I do not know the site conditions, I will just rely on the statement. I would clearly tend to recommend drainage here, as it is cheaper to implement if allowed. Theoretically, infiltration of rainwater into the sands should also be possible... but that is another topic.

Foundation:
The topsoil must be removed, that is clear. Nothing more was demanded by the geotechnical engineer.

1. If you want to found without foundations (frost skirts/strips), you must ensure the frost-proof structure up to your planned foundation base. However you manage that (more filling, more excavation, shifting the foundation level, etc.)
2. Frost skirts serve only against frost and are not responsible for load transfer. Here, after the topsoil is removed, well-compacting material can theoretically be backfilled.
3. Loads are transferred through the strip foundations (the report should have details here) into the ground. The structural engineer calculates the number, location, and dimensions of the foundations. The topsoil must be removed and the "void" up to the concrete slab (up to the insulation) must be backfilled. Here too, I would use compactable material (does not have to be F1), although the slab itself does not carry loads.

Soil analysis:
I would wait with an analysis. This concerns topsoil that should actually be characterized according to [BBodSchV]. But who knows what the earthworks contractor intends with it. So if the disposal route is clarified, then ask the earthworks contractor which analysis they need and have exactly that done.

Regards

Wow, many thanks for the detailed answer!

The soil report states:
"Frost impact zone I is present here, so the embedment depths of the frost skirts must be > 0.80 m deep"

Frost resistance:
As I understand you, either excavation is done over the entire area >0.8m and filled with F1, or only the topsoil up to approx. 0.5m is removed and instead a frost skirt or strip foundation >0.8m deep is used. In the end, it will probably be a matter of cost.

Pressing water:
Here again, I understand the situation such that either excavation would have to be done over the entire area down to the Middle Sand (>1.5m) or a ring drainage is used accordingly. Again, in the end, it will be a simple cost question.

Thanks again!

If I understand the drawing correctly, it is calculated at about +0.4m above GOK. I have attached the picture. Am I interpreting this correctly?

The drawing is difficult to understand. What is the purpose of piling up the soil so that the rainwater then flows towards the terrace? Also consider the recommended relocation of the house because of the turning area.