Ancillary construction costs for earthworks according to soil report

Yes, it will go in that direction. Then you have to compare it with your contract, you only pay 0.50 excavation separately. How does the top edge of the finished floor look? The inspector has "accepted" it. If it fits into the surroundings, you could possibly plan the floor slab deeper? That would mean less delivery material... But that affects planning so deeply (considering outdoor facilities, etc.) that it might already be too late for that. Have the offer from the general contractor given to you, referring to the approx. 5,000 €... I’m curious whether there will be a 1 or 2 in front of it. If in doubt, get offers yourself. The service of the general contractor (removing 30 cm of soil) is minor; if in doubt, assign everything yourself including mostly disposal. Good luck!

Yes, it will go in that direction. Then you have to check it against your contract, you only pay 0.50 excavation separately. How does the top edge of the finished floor look? The expert has "assumed" this. If it fits into the surroundings, you could possibly plan the slab deeper? That would mean less delivery material... But that impacts the planning so much (considering outdoor areas etc.) that it might already be too late for this. Get the offer from the general contractor, referring to the approx. €5,000... I am curious whether there will be a 1 or 2 in front of it. In case of doubt, get offers yourself. The general contractor's service (removing 30 cm of soil) is minimal, in case of doubt do everything yourself including most of the disposal. Good luck!

So I hope that I really will not need more than €10,000.

so I really hope that I won't need more than the €10,000.

Could fit.
On an area of about 10 x 15 m, we also had to replace down to about 80 cm deep. According to the construction service description, 30 cm excavation without removal was agreed. There was a small cellar, whose demolition and filling were agreed separately. Otherwise, we also had a mixture of sand and debris (from a house that once stood there before ours, back then they weren’t so strict about hauling away, remains were simply buried if they didn’t cause problems). We paid about €5,500 for the replacement.

Could fit. We also had to have an area of about 10 x 15 m exchanged to a depth of about 80 cm. According to the construction service description, 30 cm were agreed to be scraped off, but without removal. There was a small cellar, the demolition and filling of which were agreed separately. Otherwise, we also had a mixture of sand and rubble (from a house that once stood there before ours, in the past they didn't pay much attention to removal, remains were just buried if they didn't bother) We paid about €5500 for the exchange.

thanks, that sounds reasonable. Our construction advisor said that because of the missing height reference we cannot yet make a concrete offer but only after the planning. But my father knows some civil engineering companies and is just going to get an offer for 10x12m exchange 80cm.

My father once easily obtained a quote for 80cm excavation on 110m2 including backfilling and compacting. It is around €5300. So it should be fine.