Answer:
RFEM and RSTAB use a variation of the subgrade reaction modulus method. The relation to stiffness modulus ES is not possible.
In RFEM, a multi-parameter foundation model has been implemented. This can be used to carry out a very realistic settlement calculation.
The problem, however, is to find precise values for the parameters Cu,z, Cv,xz, and Cv,yz. For this, you can use the Geotechnical Analysis add-on (for RFEM 6) or the RF-SOILIN add-on module (for RFEM 5): The subgrade parameters are calculated from the loads and the data of the geotechnical report (stiffness modulus or modulus of elasticity and Poisson's ratio, specific weights, layer thicknesses) for each individual finite element using a nonlinear method.
These parameters are load-dependent and influence the behavior of the structure. The results of this iterative process are realistic settlements and internal forces in the structure.
