I am modeling shallow and shell foundations on sand using ABAQUS/CAE software. I'm modeling the soil as elastic - plastic Mohr Coulomb and linear - structures with frictional interface between the two materials. I get load curves showing settlement, but no discontinuity or "peaks" showing me the value of ultimate load of the foundations. I get only parabolic curves extending to infinity without asymptotes. I have tried different methods to identify the ultimate load (from a value estimated according to equations of Meyerhof, Terzaghi, etc.) but nothing works. Does anyone know how to determine the load capacity with these results?