Modeling of the soil flexibility using the ground elements

Hi,
I would like to ask a question about the modeling of the ground elements. I' m trying to use these elements in order to simulate the flexibility of the soil beneath a bR/C building, but I have some problems. I would like to ask If foundation beams must be placed too. Should the ground elements be placed between the same joints used as start- and end-joints of the foundation beams? I tried to put the ground elements between the same joints used as start- and end-joints of the foundation elements and I had problems with the stability of the building.

Any help or idea would be usefull
Thank you in advance for your response