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I am currently learning how to develop a numerical model for a retaining wall. If you have any example models or references, I would greatly appreciate them.
In one of the sample models I found, several lines appear during the post-processing stage. Why are these lines generated, and what do they represent?

In one of the sample models I found, several lines appear during the post-processing stage. Why are these lines generated, and what do they represent?

In that example the contact elements use the Lagrange Multiplier approach.
To store the Lagrangian DOF they create new fictitious nodes (the ones you see there)