Thanks for your help NRP99 and FEAway. I could import the .inp files by importing "part".
I just noticed that pipe-soil interaction elements can only be used with "beam" pipes, and not "shell" pipes. Am I right? And as Abaqus recommendation, when there is large amount of bending moments(like cross-country pipelines with long pipes and sharp bends), pipes and bends must be modeled as "shell" parts. So, in this case, what is the best option to model the pipe-soil interaction. Specifically, how to model soil spring stiffness? Should I model the soil as a deformable soil extrude or sweep and put the pipe system inside it and use "interaction" to simulate the soil spring values in three(or four) directions?