User-Defined Slip Surfaces

The user-defined method evaluates a single slip surface that you draw yourself, rather than searching a family of candidates. The surface is analyzed once with the selected analysis method(s), and the factor of safety is reported.

How it works

1. Select User-defined as the search method.
2. Draw the slip surface as a polyline of two or more points.
3. Run the analysis. The surface is evaluated once and its factor of safety reported for each selected analysis method.

The drawn polyline must progress from one side to the other (strictly increasing horizontally) with distinct endpoints. If you draw exactly three points, the surface is fitted to the circle passing through them where possible; otherwise the points are treated as a polyline.

Use cases

• Back-analysis — reproduce a known or observed failure surface and back-calculate the strength parameters that give a factor of safety of 1.0.
• Checking a specific surface — evaluate a surface identified by another method, a previous study, or field observation.
• Comparison and verification — confirm a hand calculation or a result from another program against a precisely specified surface.

Note Because only the surface you draw is evaluated, the result is the factor of safety of that surface, not the critical (minimum-FS) surface for the slope. Use a search method to locate the critical surface.