Boundary Conditions

The boundary conditions in a numerical model consist of the values of field variables (e.g., stress, displacement) that are prescribed at the boundary of the model. Boundaries are of two categories: real and artificial. Real boundaries exist in the physical object being modeled (e.g., a tunnel surface or the ground surface). Artificial boundaries do not exist in reality, but they must be introduced in order to enclose the chosen number of elements (e.g., blocks). The conditions that can be imposed on each type are similar; these conditions are discussed first. Then (in Artifical Boundaries), some suggestions are made concerning the location and choice of artificial boundaries, and the effect they have on the solution.

Mechanical boundaries are of two main types: prescribed displacement and prescribed stress. A free surface is a special case of the prescribed-stress boundaries. The two types of mechanical boundaries are described in Stress Boundary and Displacement Boundary. Viscous boundaries, which are used for dynamic analysis, are described in the documentation fo the dynamic option (Boundary Conditions).

• Stress Boundary
  • Applied Stress Gradient
  • Changing Boundary Stresses
  • Checking the Boundary Condition
  • Cautions and Advice
• Displacement Boundary
• Real Boundaries – Choosing the Right Type
• Artificial Boundaries
  • Symmetry Planes
  • Boundary Truncation – Location of the Far-Field Boundary