Interface in PLAXIS 3D

What is the effect of providing INTERFACE while simulating a model in PLAXIS 3D, what are the significance of POSITIVE INTERFACE and NEGATIVE INTERFACE ?

Soil Mechanics / Geotechnical Software Computational Geomechanics

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Votes: 1

Micha Van der Sloot

Hi Dinesh

For interfaces in PLAXIS, the notation of a positive or negative interface does not have any impact on the mechanical behavior. It is a notation to tell at which side of the surface the interface between the adjacent soil and this surface is located.

The positive side is derived from the local axis of the surface. Axis 1 and -2 are in-plane exes, while axis 3 is perpendicular to the surface. Using the right-hand rule for the winding, you can determine the positive side of the surface, and so here is also the location of the positive interface. For the mechanical or groundwater flow behavior, the name does not matter, as that the behavior iscontrolled by the mechanical properties (stiffness, strength, and the associated Rinter value) and the conductivity values.

So, visually check if the interface you want to use is on the correct side, especially when you want to define an interface on only one side.

A more detailed description of the interfaces can be found here:


Kind regards,

Micha van der Sloot
Bentley Systems, Geotechnical | PLAXIS