When the Surface Type in the Surface Options dialog is Non-Circular, you can define:
Specific non-circular slip surfaces, and / or
A critical surface search to attempt to find the slip surface with the overall minimum safety factor for a given slope.
TIP: see the Slide Search Methods article for an overview of the different search methods in Slide and suggestions for using them effectively
Specific Non-Circular Slip Surfaces
Specific non-circular slip surfaces are added to a model with the Add Surface option in the Surfaces menu. Any number of specific non-circular slip surfaces can be added to a model.
Non-Circular Surface Search Methods
There are FIVE different Search Methods available in Slide for locating critical NON-CIRCULAR slip surfaces:
Auto Refine Search
See the above topics for complete descriptions of these Search Methods.
For a given analysis, only ONE Search Method can be used, you cannot run multiple Search Methods at the same time.
However, specific non-circular surfaces AND a critical surface search can be defined and analyzed for the same model, this does not cause any problems.
A supplementary optimization can be applied to slip surfaces, after the initial analysis, in order to locate slip surfaces with an even lower factor of safety. See the Optimize Surfaces topic for details.