6.4.1        Boundary conditions


Boundaries are either real or artificial. Real boundaries in slope stability problems correspond to the natural or excavated ground surface that is usually stress free. All problems in geomechanics including slope stability problems require that the infinite extent of a real problem domain be artificially truncated to include only the immediate area of interest. Figure 15 shows typical recommendations for locations of the artificial far-field boundaries in slope stability problems.


Artificial boundaries can be of two types: prescribed displacement or prescribed stress. Prescribed displacement boundaries inhibit displacement in either the vertical or the horizontal direction, or both. Prescribed displacement boundaries are used to represent the condition at the base and the toe of the slope model. Displacement at the base of the model is always fixed in both the vertical and horizontal directions to inhibit rotation of the model.


The far-field boundary location and its condition must be specified in any numerical model for slope stability analyses. The general notion is to select the far-field location so that it does not significantly influence the results.  In most slope stability studies, a prescribed-displacement boundary is used.


Figure 15: Typical recommendations for locations of artificial far-field boundaries in slope stability analyses.