ᐅ Excavating a strip foundation in poor soil conditions

Hello everyone,
I’m new here. My name is Tobias, I’m 30 years old, and I work as an electronics technician.
That’s a bit about me.

Now for my first question.
It turns out that the soil on the plot is quite poor, meaning there is groundwater at about 1 meter (3 feet) depth, and solid ground only starts at 2.2 meters (7 feet).

The architect suggested that the best approach would be to place continuous strip footings under all the load-bearing walls. So, at those positions, excavate down to 2 meters (6.5 feet) and fill with concrete and steel reinforcement.

I have a few questions regarding this:
1. Has anyone had experience with such poor soil and possibly a high groundwater table and could share some tips?

2. Does the rest of the soil within the strip footing area also need to be excavated down to 2 meters (6.5 feet) and backfilled with gravel? Or would a depth of only 0.5 to 1 meter (1.5 to 3 feet) be sufficient in those areas?

3. Is it possible to roughly estimate the cost per cubic meter (cubic yard) for this type of work?

Thank you for your help.

Soil replacement is expensive.

What does the soil report say about the foundation recommendation?

First, one would need to define what exactly is meant by stable soil starting at 2 meters (6.5 feet) depth and what lies beyond that. The geotechnical engineer or structural engineer, in cooperation with the geotechnical report, then provides a foundation recommendation—not the architect.

It is recommended to raise the house slightly above ground level by 30-50 cm (12-20 inches) and to place 30-40 cm (12-16 inches) of washed gravel under the foundation slab. Talk directly with the person who conducted the soil survey, as they should know what is necessary.

The advice from architects can always be somewhat variable.

The soil report is based on samples taken from the road directly in front of the property. Boreholes were drilled throughout the entire new development area, but not directly on the individual plots. However, the general conditions can be roughly inferred, as the soil is poor everywhere.

Regarding the soil layers:
0.3 meters (1 foot) topsoil
0.8 meters (2 feet 7 inches) fine sandy clay, very moist
1.0 meters (3 feet 3 inches) strongly fine sandy clay
2.2 meters (7 feet 3 inches) clay, organic, silty
Groundwater at 1.0 meter (3 feet 3 inches) depth

I have not yet purchased the plot, so there is no soil report for the property itself or a structural engineer’s calculation available.

Orgasmic .. And what is underneath that? Or does the drill profile end there?