Can pre- or post-tensioning be modeled in Slide?

There is no way to put a pre- or post-tensioning force into Slide.  Since Slide is a limit-equilibrium program, all support is modeled as simple force being put back into the system to stabilize the slope.  The magnitude of this force depends on the capacity of the bolt against tensile, pullout or stripping failure mechanisms. 

Ultimately, each support element in Slide only applies a single force to the sliding mass, using either the Active or Passive assumption. Please review the Overview of Support Implementation help topic for more information.

In particular, note the "Interpretation of Support Force Diagrams" described in this topic:

The user should appreciate that a support Force Diagram, as implemented in Slide, does not necessarily represent the true state of stress or loading mobilized by a given support element. The Force diagram simply represents the maximum available force, which a given support element can theoretically apply to the sliding mass, at any point along its length. This is based on the assumptions described for each support type in Slide.

Remember that the Slide analysis is a limit equilibrium analysis. Displacements and strains are not considered in such an analysis. In order to realistically model the interaction of support and slope, and to calculate actual strains and loading mobilized within the support, more sophisticated numerical analysis methods are required, such as finite element or finite difference methods.

The modeling of support in Slide is a simple but useful method, of accounting for the effect of the SUPPORT SYSTEM on the SLOPE, in a limit equilibrium slope stability analysis. It is not intended to model the effect of the SLOPE on the SUPPORT SYSTEM, and the support Force Diagrams should not be interpreted in this way.