The interface properties are defined by the parameter Rinter that can be set in the Interfaces tab sheet of a soil material set. When the Interfaces tab sheet is skipped, the Rinter parameter will have a default value of 1.0 (rigid). The Rinter parameter relates the strength of the interfaces to the strength of the soil, according to the equations:
tanφinter = Rinter tanφsoil and Cinter = Rinter Csoil
With the default value Rinter = 1.0 (rigid), Cinter = Csoil and φinter = φsoil. In general, strength properties in the interaction zone between soil and structures are lower than the adjacent soil. This reduction can be specified using the Rinter parameter. Hence, using Rinter < 1.0 gives a reduced interface friction and adhesion compared to the friction angle and the cohesion in the adjacent soil.