Generalized Anisotropic
Direction-dependent strength via the generalized anisotropic model.
The Generalized Anisotropic model gives a material a strength that depends on the inclination of the slip surface at each slice base. It does this by combining other materials from the catalog: a child (weak-direction) material is applied when the slice base aligns with a defined direction, and a base material is applied elsewhere. This is the model to use for bedded, foliated, or jointed ground whose strength varies with orientation.
It is the most configurable strength model. The sections below describe each choice in the editor, top to bottom.
Input type
| Input type | Description |
|---|---|
| Angle range | Strength is selected from discrete angle bins. Each row defines a start/end angle (0–180 degrees) and a material. The slice's base angle picks the matching bin, and that material's full strength is used (weight = 1). If no bin matches, the base material is used. |
| Angle or surface | Strength is direction-weighted and blended with the base material using a mapping function. This is the richer mode and exposes the definition, mapping, and joint-treatment options below. |
Base material
A base material is chosen from the catalog. It supplies the strength away from the weak direction and, in angle or surface mode, the strength that the child material is blended against.
Anisotropy definition (angle-or-surface mode)
This controls how the weak direction is located at each slice base:
| Definition | How the local direction is determined |
|---|---|
| Angle | Each row specifies a fixed plane orientation (degrees). The offset is the difference between the slice base angle and that orientation. |
| Surface | Each row references an anisotropic surface drawn in the geometry. At each slice base, the nearest point on the surface is found and its local tangent angle is used. The closest surface (by distance) wins. |
| Vector field | Each row references an anisotropic vector field. The field's orientation nearest the slice base point gives the local direction. |
Surfaces and vector fields are created in the geometry editor — see Anisotropic Geometry.
Mapping function
The mapping function converts the angular offset between the slice base and the weak direction into a child weight from 0 to 1 (1 = full child strength, 0 = full base strength). Offset is measured as the acute angle between planes (0–90 degrees).
| Mapping | Child weight vs. offset |
|---|---|
| A-B (direct) | Weight = 1 for offset up to a_deg, then ramps linearly down to 0 at b_deg, and stays 0 beyond. Each row supplies its own a_deg and b_deg (0–90, with b ≥ a). |
| Linear | Weight = 1 - offset/90. Decreases linearly across the full 0–90 range. |
| Cosine | Weight = (1 + cos(pi * offset/90)) / 2. A smooth cosine taper from 1 at 0 degrees to 0 at 90 degrees. |
The child and base strengths are then combined by weight:
tau = child_tau * weight + base_tau * (1 - weight)Joint treatment
When more than one direction (row) is active at a slice, the joint treatment decides how the candidates combine:
| Treatment | Behavior |
|---|---|
| Worst-case (default) | Each active candidate is evaluated and the weakest resulting strength is used. |
| Closest | Only the candidate whose direction is nearest the slice base angle is used. |
| Blend | All active candidates plus the base are combined by their weights into a single weighted-average strength. |
Surface and vector-field definitions resolve to a single nearest candidate, so joint treatment mainly affects the angle definition with multiple rows.
Use base if weaker
An optional Use base if weaker toggle (on by default) compares the resolved anisotropic strength against the base material's strength at the same normal stress. If the base material is weaker, the base strength is used instead. This prevents the anisotropic combination from reporting a strength higher than the intact base material.
How it feeds the solver
At each slice base the model resolves to an effective material/strength, which is
then evaluated like any other criterion to produce an equivalent Mohr-Coulomb
(c, phi) for the factor of safety. Because the child and base materials can each
use any criterion (Mohr-Coulomb, Hoek-Brown, or a shear function), the anisotropic
result inherits whatever strength model those materials use.
Worked example
A foliated rock slope: set the base material to intact rock (Hoek-Brown),
add an angle row pointing along the foliation at, say, 30 degrees with a weak
Mohr-Coulomb child material, and use the A-B mapping with a_deg = 5,
b_deg = 20. Slip surfaces within 5 degrees of the foliation get the full weak
strength; between 5 and 20 degrees the strength ramps toward intact rock; beyond
20 degrees the intact rock strength governs. With Use base if weaker on, the
result never exceeds the intact rock strength.