FLAC3D Theory and Background • Interfaces

General Comments

There are several instances in geomechanics in which it is desirable to represent planes on which sliding or separation can occur. For example:

  1. joint, fault, or bedding planes in a geologic medium;

  2. an interface between a foundation and the soil;

  3. a contact plane between a bin or chute and the material that it contains;

  4. a contact between two colliding objects; and

  5. a planar “barrier” in space, which represents a fixed, non-deformable boundary at an arbitrary position and orientation.

FLAC3D provides interfaces that are characterized by Coulomb sliding and/or tensile and shear bonding. Interfaces have the properties of friction, cohesion, dilation, normal and shear stiffnesses, and tensile and shear bond strength. Although there is no restriction on the number of interfaces or the complexity of their intersections, it is generally not reasonable to model more than a few simple discontinuities with interfaces because it is awkward to specify complicated interface geometry. The zone joint logic should be used for the specification of more complicated discontinuities in FLAC3D, though the logic is currently limited to small-strain analyses. The program 3DEC (Itasca 2007) is specifically designed to model many interacting bodies in three dimensions in large strain; it should be used instead of FLAC3D for large-strain modeling.

Interfaces may also be used to join regions that have different zone sizes. In general, the zone attach command should be used to join grids together. However, in some circumstances, it may be more convenient to use an interface for this purpose. In this case, the interface is prevented from sliding or opening because it does not correspond to any physical entity.