Slice Generation
How the failure mass is discretized into slices.
Before any method runs, JW Slope divides the sliding mass above a trial slip surface into vertical slices. Every LEM method starts from the same slices, so the slicing rules below apply regardless of which method you select.
Target number of slices
The Target Number of Slices (default 30, minimum 8) sets how many slices the slicer aims to create. It is a target rather than an exact count: the slicer first places any required slice boundaries (see below), then distributes the remaining slices to keep slice widths roughly even, so the final count can differ slightly from the target.
A higher count gives smoother per-slice results and slightly more accurate factors of safety at the cost of speed. The default of 30 is adequate for most slopes.
Automatic (required) slice boundaries
Beyond the two surface endpoints, the slicer inserts a slice boundary wherever the slip surface crosses a feature that the strength or pore-pressure calculation needs to resolve cleanly. These insertions are controlled by advanced options (all default on; see Advanced Options):
| Feature | Advanced option | Default |
|---|---|---|
| Material boundary crossings (slip surface or exposed slope) | Slice at Material Boundaries | On |
| Phreatic surface / piezometric line crossings (water-table pore pressure) | Slice at Phreatic Surface Intersection | On |
| FEA phreatic surface crossings (FEA groundwater pore pressure) | Slice at Phreatic Surface Intersection | On |
Generated surfaces may also carry their own preferred boundary positions, which are honored as required boundaries.
Why required boundaries matter
Without a boundary at a material or water crossing, a single slice would straddle two different materials or two different pore-pressure regimes, smearing the strength and pore force over its base. Required boundaries keep each slice base within one consistent region.
Distributing slices
The required boundaries fix the segments that must exist. The slicer then distributes the target number of slices across those segments in proportion to their width, so each region is sliced about as finely as the overall target implies, and slice widths stay roughly uniform.
Tension-crack clipping
If a tension crack applies, the trial surface is clipped at the tension crack before slicing, so the sliced mass does not extend past the crack. Tension-crack forces (for example water pressure in the crack) are then applied to the affected slice.
Invalid surface: too many required boundaries
The number of required boundaries can exceed what the target slice count allows. If the required boundaries alone would need more slices than the Target Number of Slices, the surface cannot be sliced and is rejected with the reason required slice boundaries exceed slice count. The search records this so the UI can summarize why surfaces were skipped.
If many surfaces are rejected for this reason
Raise the Target Number of Slices. A geometry with many closely spaced material or water crossings needs enough slices to place a boundary at each crossing and still have slices in between.
Other slicing behavior
- The toe slice is forced triangular so the exposed toe does not produce a sliver with a false vertical edge.
- Each slice stores its geometry, area and centroid, base length and inclination, sampled material strength, pore force, and accumulated loads and seismic forces, which the analysis methods then consume.