Slip Surface Search Overview

The slip-surface search finds the surface with the lowest factor of safety. JW Slope offers several search methods, from a fast automatic circular search to population-based metaheuristics for non-circular surfaces, plus an option to evaluate a single surface you define yourself.

Choosing a search method

The search method is selected from a single menu in the slip-surface settings:

The three metaheuristic methods (PSO, Cuckoo, DE) optimize non-circular polyline surfaces using the block-search window as their starting geometry.

A search complexity slider (Very low to Very high) lets you scale a method's search effort up or down by adjusting its underlying parameters together; the documented per-method defaults below correspond to the medium setting and to the raw default settings.

Surface-altering optimization

Any search can be followed by an optional surface-altering post-processing step that perturbs the critical surface's geometry to find a lower factor of safety. It is off by default. See Surface-Altering Optimization.

Failure direction

Set the failure direction to tell the solver which way the mass slides:

• Left to Right (default)
• Right to Left

The failure direction also fixes the sign convention for seismic loading.

Slope limits

By default, the left and right ends of candidate surfaces are bounded by limits computed automatically from the slope geometry. You can optionally enable custom slope limits to restrict the search to specific left/right ranges. A second limit set can be enabled so that the left endpoint and the right endpoint are constrained to different ranges.

Weak layers

When weak layers are present, candidate surfaces can be snapped or clipped to follow them. The behavior is controlled by the weak-layer handling mode. See Weak Layer Handling.

Automatic slice boundaries

Regardless of method, the solver inserts slice boundaries at the locations where the surface crosses important features, so that each slice has uniform properties along its base. By default this includes intersections with:

• the water table,
• piezometric lines,
• the phreatic surface, and
• material boundaries.

These are controlled by advanced settings (all on by default). Tension-crack locations are also forced as slice boundaries when a tension crack truncates the surface.