Soil report: CSV columns?

Hello everyone,

we are planning the construction of a single-family house (with a basement). We are interested in a 640m² plot of land. I received the relevant soil report of the plot from the real estate agent. It shows that a foundation on CSV columns is recommended, here is the excerpt from the report:

The foundation can be placed in the technically critical loess clay soils if a soil improvement is carried out. We recommend lime stabilization columns (CSV columns) to reinforce the ground. The lime columns must be screwed into the ground in a suitable grid. The DGGT information sheet on lime stabilization columns must be observed. The loess soils have an undrained shear strength of at least 15kN/m², so the safety against buckling is ensured. The lime stabilization columns must be installed at least 2m into the tertiary gravel sands.

The loess clay layers are extremely sensitive to weather and frost, i.e., the excavation must be carried out very carefully and only when dry. The final excavation must be done stepwise with a smooth bucket. The dry exposed excavation base must be immediately sealed with geotextile and a 0.4m thick gravel cushion made of gravel sands of soil group GW according to DIN 18196 and must not be driven on. If the construction site is left over the winter, care must be taken that already completed components do not freeze from below or the ground freezes.

The construction of the basements including partition walls must be carried out with reinforced concrete construction on an elastically bedded base slab for bracing. The semi-detached houses must be statically decoupled from each other by movement joints.

On the ground improved with CSV columns, the foundation can be designed according to DIN 4018 using the stiffness or bedding modulus method. The following characteristic input values are permissible for preliminary design:

Stiffness modulus Es = 50MN/m²
Bedding modulus ks = 30MN/m³

Foundations with individual and strip footings are not recommended.

For frost safety reasons, it is necessary to ensure that all above-basement components are founded at frost-free depth, i.e. at least 1.2m below the future ground surface. Alternatively, a frost screen or frost skirt can be implemented.

Is it possible to roughly estimate what additional costs such a foundation would entail? For a "normal" pile foundation, I was given a rough guideline of 20,000-30,000€.

Are there alternatives to this, for example a slab foundation under the basement or similar?

Thank you very much for your help.

If the pillars have to go 2 meters into the ground: for a house with or without a basement? Does the soil stabilize at that depth? What is the soil composition / earth layers?

Around the corner from us, I know builders where it is like this:

If they build with a basement, they don't have to worry about anything because the soil at that depth supports everything without any problems. The neighbor builds without a basement and has to lay over 1.50m of gravel bed and geogrids for the foundation.

First of all, thank you very much for the response.

As a layperson, it is difficult for me to interpret from the report how load-bearing the soil is further down. The composition is as follows:

0.00m - 0.20m topsoil
0.20m - 7.00m silt, sandy, slightly gravelly, stiff, semi-solid, brown

I would inquire on what development basis the foundation recommendation (i.e., house with or without a basement) is based. It is - especially for laypersons - not clear what to make of the soil report. Even less so if the building to be constructed is not considered in the report.

In our report, for example, there is partially direct reference to our house to be built. This is not possible for the report you have, since the surveyor does not even know what will be built on it. Something different could perhaps even result. Perhaps, for example, a thick gravel bed might be sufficient for a house with a basement instead of the pile foundation. But that can only be determined if it is clear what and how something is to be built.

Hello emer,

thank you for the hint. I will simply call the engineering office. Asking costs nothing and maybe they could answer exactly these questions.

A gravel bed under the cellar would of course be ideal. Let's see if we are that lucky.

Best regards