Which material/granulation is suitable for the foundation of a single-family house without a basement?

Hello everyone,

according to the soil report, we are supposed to fill up to a depth of 0.6 m for the foundation, i.e. to replace the soil. [...] Furthermore, a bedding layer at least 30 cm thick made of well-graded gravel or comparable RC material with a compaction degree of Dpr ≥ 98 % is to be installed below the base slab.

The achieved bearing capacity is to be verified by plate load tests. EV2 values ≥ 70 MN/m2 or EVd values ≥ 35 MN/m2 must be demonstrated on the bedding cushion. For the static preliminary design of the foundation, the design value of the base pressure is to be limited to R,d = 280 kN/m2 (zul = 200 kN/m2). In the design according to the bedding modulus method, the bedding modulus can be assumed as ks = 15 MN/m2. [...]

Unfortunately, the material for the fill is not specified in more detail and "well-graded gravel" is unfortunately open to interpretation for the bedding layer as well.

Which material in which grain size should we use? Most of the time I read about 16/32 gravel ...

If more information from the soil report is required, I can gladly provide it.

Thank you very much for your support!

The geologist conducting the soil survey would be my first point of contact. The second would be the [Tiefbauer].

Hello,

generally, gravel with the grading 00/32 or 00/45 is used for single-family houses. The fine grain content is necessary so that the material can be compacted well.
With the required EV2 values, theoretically a sand mixture can also be used (this is done in the North, where there is no gravel, or it is very expensive). However, I would tend to the aforementioned grain sizes, which will save problems later.

Since you are only installing 60 cm, I assume that you are planning frost skirts or strip foundations for frost protection. Therefore, the material does not require additional certification as frost protection material.

Naturally, natural materials such as basalt gravel/limestone etc. can of course be used. It naturally depends on what is available in your region.

Alternatively, recycling material is a cheaper and, in my opinion, also a good alternative. However, the material must be approved by the responsible authority, as it is legally considered "waste."

PS: even though this doesn't really belong here, I am of the opinion that material which has been extensively processed, undergone various tests, and meets the required limit values should no longer be classified as waste.

Best regards

The geologist conducting the soil survey would be my first point of contact. The second would be the civil engineer.

So my first point of contact in such a case would be the structural engineer... the soil surveyor measures the actual state of the ground and gives certain recommendations for the foundation, but the structural engineer calculates it specifically and also determines which gravel is necessary. It is also not unimportant what is to be built on it, bungalow or multi-family house with 4 floors, the soil surveyor does not know that.

After the soil survey, I certainly received a structural engineering report that precisely stated what the civil engineer should do.

I would not ask the civil engineer at all. Because he dumps in the gravel specified by the structural engineer.

So my first point of contact in such a case would be the structural engineer... the soil expert measures the actual condition of the ground and gives certain recommendations for the foundation, but the structural engineer calculates it concretely and also determines which gravel is necessary. It is also not entirely unimportant what is to be built on it, a bungalow or an apartment building with 4 floors, the soil expert does not know that.

After the soil report, I definitely received a static proof that precisely stated what the earthworks contractor should do.

I would not ask the earthworks contractor at all. Because he dumps the gravel prescribed by the structural engineer.

Hello,
unfortunately, that is not quite correct.

The structural engineer does not have expertise in soils, soil parameters, or material properties. Exceptions prove the rule.
The soil expert, as described above, is responsible for this. He specifies the foundation and the assumed soil parameters and soil pressures, or bedding modulus. The soil expert knows the location and dimensions (single-family house, apartment building, hall, etc.) of the construction project. The structural engineer takes these values and calculates the structural design for the building based on them. From this, the necessary reinforcement and the number, position, and width of the foundations are determined.

The material is specified by the soil expert. However, to avoid restricting the client too much, some leeway is allowed here (≥ 98% Proctor density, EV2 of ≥70 MN/m²). The earthworks contractor can actually assist here, as he can say which material he can get at which price.

As said, soil expert or earthworks contractor for material questions and execution. The structural engineer then calculates later whether it fits the building.