Hi ArraynThe method we use is based on a textbook Dynamics of Bases and Foundations by D. D. Barkan, it is a very old text that is no longer in print. I have also been reviewing Handbook of Machine Foundations by P. Srinivasulu and C. V. Vaidyanathan, but I have not had an opportunity to correlate this with a model/measurement yet.nBoth of these books are based on determining the static stiffness of the soil and it's effect on the 6 fundamental frequencies. The results are not frequency dependent, and it only applies to low frequency dynamics. Unfortunately I do not believe it is suitable for what you are trying to acheive.nI am not familiar with the impedance function method, my only knowledge of it is it's applicability in acoustics. There is some info in the APDL help, although I do not know if this leads to any useful references on calculation.n