Analysis Methods Overview
Limit-equilibrium methods and the experimental FEA solver.
JW Slope evaluates each trial slip surface with the limit-equilibrium method (LEM): the failure mass is cut into vertical slices, and a factor of safety (FOS) is computed as the ratio of available shear strength to mobilized shear along the base of those slices. Four LEM methods are available. They differ in which equilibrium conditions they satisfy and how they treat the forces between adjacent slices.
The four methods
| Method | Equilibrium satisfied | Interslice forces | Surface type | Kernel |
|---|---|---|---|---|
| Bishop Simplified | Moment (about circle center) | Normal only; interslice shear assumed zero | Circular | TypeScript |
| Janbu Simplified (Uncorrected) | Horizontal force | Normal only; interslice shear assumed zero | Circular or non-circular | TypeScript |
| Spencer | Force and moment | Parallel resultants at a single constant angle | Circular or non-circular | GLE C++ (WASM) |
| GLE / Morgenstern-Price | Force and moment | Variable, scaled by lambda * f(x) | Circular or non-circular | GLE C++ (WASM) |
Bishop and Janbu are simplified methods: each satisfies only one equilibrium condition and ignores interslice shear, so each makes a single static assumption that closes the problem. Spencer and GLE / Morgenstern-Price are rigorous methods: they satisfy both force and moment equilibrium by solving for the interslice force inclination, so they generally give more defensible results on complex geometries at higher cost.
Shared rigorous kernel
Spencer and GLE / Morgenstern-Price are both solved by the same C++ general
limit-equilibrium (GLE) kernel compiled to WebAssembly. Spencer is the special
case of GLE with a constant interslice function, so it runs through the same
solver with a constant f(x) rather than separate code. Bishop and Janbu remain
in TypeScript because they are light by comparison.
Choosing a method
- Circular search, quick screening — Bishop Simplified is the default and is well established for circular surfaces.
- Non-circular / block surfaces — use Spencer or GLE / Morgenstern-Price, which satisfy full equilibrium and are formulated for arbitrary surfaces. Bishop is intended for circular surfaces.
- Conservative force-equilibrium check — Janbu Simplified (uncorrected). No correction factor is applied (see the Janbu page), so results are typically conservative.
- Reference / defensible final result — a rigorous method (Spencer or GLE). GLE additionally lets you select the interslice force function (see Interslice Functions).
Running several methods at once
The Analysis Method panel is a checklist: you can enable more than one method for a single run. Every method you select is evaluated on the same set of trial surfaces, and each method keeps its own critical surface and FOS. At least one method must remain enabled.
When more than one method has results, the display filters by a single method at a time, so you compare critical surfaces and factors of safety method by method. The selected filter also controls which result the plotted critical surface, slices, and line of thrust correspond to.
The experimental FEA solver
JW Slope also includes an experimental finite-element capability. It is not a fifth selectable LEM method; instead it appears as the FEA-LEM Check option (see Advanced Options). When enabled, the app solves an elastic stress field and integrates stresses along the LEM critical surface to report an independent FOS next to the limit-equilibrium result, as a comparison. The elastic stress field can also drive the experimental FEA Stress interslice function in GLE.
Experimental
FEA-based features are experimental and intended for comparison and exploration, not as a primary design basis.