Hello colleagues! 

Im trying to create a model to see result of global buckling of a pipeline.

And Im stuck here with soil and pipe interaction problem. Here is friction coefficient that im trying to mimic.

"http://origin-ars.els-cdn.com/content/image/1-s2.0-S0029801813002035-gr4.jpg"

the graph shows dependency of lateral friction coefficient  on lateral displacement. 

My thought on this problem is that this dependency cannot be represented using built-in friction module but it can be represented user subroutine "FRIC"

I want to know if i am on right track.

Studying the manual, there was one part that i could not find. In 'penalty and Lagrange multiplier formulations' friction coefficient can be dependent on contact pressure, slip rate and etc, In the manual i could not find formulation showing  how these variable are dependent on one and other. So here i don't know how friction coefficient would look like if i insert any of this parameter.  If one could explain or point out where i can read more about it, ill be really thankful

Tank you very much