GGU-FOOTING: Determining the mean governing soil properties
In the case of stratified subsoil, the soil parameters can be averaged above the bearing capacity failure plane in accordance with DIN 4017, which is composed of the two linear components of a logarithmic spiral. The governing parameters are summarized in the following figure:
The mean governing soil properties are determined using the following relationships:
cal tan φ = Σ tan φ i · li’ / Σ li
cal c= Σ ci · li’ / Σ li
cal γ2 = Σ γ2i · Ai’ / Σ Ai
li = length within individual layer
Ai = area of individual layer
The condition for the permissibility of the mean is that the mean friction angle demonstrates a maximum deviation of 5° to the true friction angles. This condition can be checked by the program. If it is not adhered to, the program reduces the largest friction angle in stages until the condition is met.
The weight of the soil above slip body GK 3 is summed, including and distributed and line loads present and converted to an idealised body γ1 · d.
Large line loads can generate a substantial increase in an imaginary embedment depth.. This is associated with soil pressures, which cannot be activated as calculations would indicate. The DIN 4017, for example, assumes that the ratio between embedment depth d and footing width b will achieve a maximum of 2.0 in order to guarantee the validity of a bearing capacity analysis. You should therefore examine your input data with this in mind. The same effect can be achieved by defining very large embedment depths.