Hello, I have a question about the interfaces in plaxis. I did a comparison between 3 cases :1. A retaining wall with a rigid interface 2. A retaining wall with a 0.6 interface coefficient 3. A retaining wall without any interface (deactivated interface)My question is about the results i got from these 3 analyses, i was expecting to get the same results for the cases 1 and 3 but it was not the case. A rigid interface is supposed to be the same as no interface so I would like to understand why there is a difference. The difference isn't huge but since the displacements for this project are measured in milimeters, a small difference has an impact.Thank you.
Dear Nihed,
That is not entirely correct. The moment you introduce an interface PLAXIS automatically splits the nodes and applies the correct "relations" to the nodes.So, in general, the two cases cannot be identical by definition as they are not entirely the same finite element mesh.
However, indeed, PLAXIS still reduces the stiffness, even for rigid interfaces, but typically this factor is large enough for any engineering project to have an effect on the results. If you have a case with very (very) soft soil, then this factor used can start showing differences when comparing it to a fully bonded connectivity (shared nodes).
In general, I recommend using an interface when needed. If you do not want to model the interface between the structure and soil (or soil and soil or soil and rock or rock and rock), then you do not need to include it at all.
Be aware that you can always use a custom material for an interface and apply directly the stiffness and strength you want to be considered for the interface behaviour.