I have post my problem in this forum, but it seems I did't express my problem clearly, now please allow me to describe my problem in a detail way:
Our jack-up platform is standing on its mat structure with 65mx65mx5m, the load will transfer from the colum structure into the mat-column connection and eventually spread out to the seabed. And now my task is to check the mat strength in different load cases. But I don't know the right way to simulate the soil(which only carries the compression, transverse force,no tensile force) beneath the mat, before I tried function spring in Non-linear analysis, I obtained one result sucessully, but it seemed unreasonable. Then I attempted gap element, but the software can not converge, then I really had no idea how to solve the application of gap element.
Those masters hovering in this forum, please give a hand and help me out, I would be very grateful, if you don't mind, it is very great you email me directly firstname.lastname@example.org