Building ground investigation report (ram core soundings) suitable or excavation?

If the 99 percent figure is correct, then that really seems to be the best option. Then the question would be what we do with the earth and the construction debris? That has to go to a landfill and they need a [laga] determination of the soil again, right? If it isn’t 99 percent, but only 50, then it might be worthwhile to have the assessment done beforehand? The idea was actually to determine through the assessment whether we need to dig a construction pit anyway / remove the old cellar and to find out immediately whether the ground beneath the cellar (if it’s still even there) is suitable.

I'll be more specific: when excavating the old basement, we will surely find different things: 1. bricks (walls) 2. earth or bricks with earth or bricks with earth with other debris (filled airspace of the old basement) and 3. earth (topsoil) on top.
3. Would one store this on the property?! 1. and 2. will be difficult to separate?! Would all of this end up as construction debris? We are talking about roughly 100 square meters times 1.5 meters height, so 150 cubic meters of construction debris under the new building, and if the entire property is cleared, definitely 250 cubic meters. Are these realistic assumptions?

The topsoil stays with you, the construction debris can be disposed of at relatively fair prices as long as it does not contain hazardous waste – asbestos, etc.

The 99% is not to be taken literally, but the risk of cavities is simply very high, even if everything appears well backfilled during test excavations. Possibly the cellar had already partially collapsed due to the bombing (rather unlikely, but it could be). An alternative foundation with concrete stilts down to the original ground beneath the old cellar and then the slab on the stilts would certainly also be possible, but that would be even more expensive.

yes, I also did not take the 99% literally. I will call the currently preferred company for the soil survey. The price includes 4 drillings and the LAGA. Maybe they will say that they do 2 drillings in the old cellar and 2 outside. That should then possibly be meaningful to determine whether there is a cellar underneath (which is to be assumed) and how it was filled in and what kind of soil is around it. Or will that not work?

Regarding the removal: topsoil to the side is clear. But does it then make sense to try to separate the earth soil (possibly with some bricks) and the construction debris (the walls and the cellar floor)?

If I remember correctly, the LAGA examination must be no older than 6 months. If you don’t proceed with the implementation by then, you could save yourself the examination for now.

So with the preferred offer, they said it is possible to make 2 of the 4 drillings outside the old building and 2 inside the old building. Then you would have certainty

[*]whether there is a basement there
[*]roughly how it is backfilled (although he also said right away: if there is one, they would not recommend building on it)
[*]how the ground next to and under the basement is

we probably don’t need more information to build?
Then there would indeed be the fact that if the LAGA may only be 6 months old, it probably makes sense to do it only when we need it. And apparently you don’t need one up to 200 cubic meters. So I could probably skip this point anyway, since I actually shouldn’t reach 200 cubic meters?!

Just a quick other question: For a residential house on a slab, how deep is usually excavated there? And for a house with a basement (let’s say a daylight basement where the floor of the first floor should protrude about 120 cm - with a 32 cm basement ceiling + floor and 255 cm clear height, the basement floor is at -167 cm) how deep does the excavation pit roughly need to be?