I am a bit confused with the application of friction coefficient, Mu.
say the soil has 1.2 lateral friction coefficient and the pipe is restraint laterally (X with K value) and vertically (+y with K value), what is the appropriate way to the 1.2 friction exerted on the pipe. should the 1.2 as Mu input for restraint X or +y or both wrong. please advice.

Is the pipe partially buried and being held laterally by soil or is the pipe simply resting on top of soil and some other type of lateral support is used? In modeling soil as a restraint you need more information than simply the friction coefficient. You also need to determine the soil stiffness and the breakaway force so you can model it with bi-linear restraint types. If you are modeling pipe resting on soil you will need to have a node approximately every 5D along the length of pipe.

thanks for your prompt response. Let say the pipe is resting on seabed and I input the +y restraint with known soil stiffness value and friction factor of, say 1.2, is it appropriate? The distance of the node will depend on the critical area of the elements. Is there any thumb rule on the distance of the vertical restraint as stated above?
Another problem that I faced is whenever I generate the animation view, the bend elements are missing. Please advice on the matter.
Thank you.

CAESAR II uses point supports, your sea floor is a continuous support. To get the CAESAR II model to "match" the sea floor, you would have to enter many, many point supports. That's not practical. We do a few things in our buried pipe modeler to address this issue:
1) to model soil friction in the axial direction, we can space these friction supports far apart without affecting the axial response due to friction
2) transverse response requires closely-spaced supports to pick up bending - in your case, you would locate more friction supports where bending occurs
3) we assume that the soil supports deadweight, therefor, we eliminate weight on buried sections so that those distant (vertical) supports (handling axial friction) do not creat a deadweight bending problem
4) since we eliminate deadweight on buried sections, the normal loads in the vertical direction are improperly defined for calculating normal loads (N). These normal loads would be used to set friction forces (mu*N; you are suggesting mu=1.2 here). So, instead of friction we use a bi-linear stiffness in the axial direction to model the hold/break-free situation with axial friction.

Does this answer your question? No. But perhaps you can now determine how close your Y supports should be - is there bending? is there weight to be carried?

And the other question - should mu=1.2? I'll leave that to others. Perhaps once you're done with this job, you can add your insights here.