Soil column

[pejman_opensees]

I have some questions about the modeling of coupled structure-pile-soil interaction considering the free field site response (soil column) and I would be so glad if anyone could answer

1) How can the dimension of soil column and the size of soil elements be
evaluated so that the response of the soil column not be affected by the response of
pile?

2) What would be the boundary conditions of soil column elements?

3) If the dimension of soil column must be evaluated by trial and error, what
would be the converging parameter?

4) Would it be possible to have a sample OpenSees data file for coupled SPSI approach?
Appreciate in Advance,