FRP Pressure Thrust

Good night:

I am designing an FRP pipe buried, and I find the following question, which I hope I appreciate any help:

- How to model the pipe buried in what refers to obtaining the correct pressure thrust allow me to properly calculate the thrust piling?.

I understand that to do the job well, I should include all existing coupling, using cnodes, or otherwise not necessary?

To do the job I'll use BS.

Thanks in advance for your help

Help Please