Hi,

Interfaces in PLAXIS can take account of proper soil-structure interaction, where relative displacements (including sliding) can occur between the structure and the adjacent soil.
More details here: https://communities.bentley.com/products/geotech-analysis/w/wiki/45944/modelling-soil-structure-interaction-interfaces

The naming in PLAXIS for these interfaces is mostly done to recognize which one is which. It is based on the (internal) direction of the line associated with the interface. It does not have a mechanical consequence if an interface is called Positive or Negative: the behaviour is controlled by the interaction, pressure equilibrium and relative movements of soil and structure causing e.g. shear stresses and -strains, and allowable shear stress in the interface.

Kind regards

Micha van der Sloot