Hyperbolic
A Hyperbolic shear strength envelope is defined by the following equation:
and 
in the Hyperbolic shear strength equation. The following figure illustrates a hyperbolic shear strength envelope.
is defined as the shear strength at 
.
is defined as the friction angle at 
.The definitions of Cohesion and Friction Angle for the Hyperbolic shear strength model. The Cohesion for a Hyperbolic shear strength envelope is actually the limiting, maximum shear strength, for high normal stress.
The Hyperbolic shear strength model has been found to characterize the shear strength of soil/geo-synthetic interfaces, and other types of interfaces [Esterhuizen, Filz & Duncan (2001)]. For example, it could be used to model the shear strength of:
- a concrete/soil interface
- a geotextile/soil interface
You may wish to use Hyperbolic strength to model the failure mode of "direct sliding" along a GeoTextile/Soil interface. In this case, you will have to define a narrow layer of soil along the geotextile, and assign a material type which uses the Hyperbolic shear strength model.