Weak Layers
Insert thin weak layers that the slip surface can follow.
Insert thin weak layers that the slip surface can follow.
A weak layer is a thin seam — a bedding plane, clay band, or other low-strength horizon — modeled as an open polyline with its own dedicated material. Because such seams are often too thin to draw as a material region, the weak-layer entity lets you assign strength along a line and have the slip-surface search route surfaces along it.
Drawing a weak layer
- Click Add Weak Layer in the Geometry panel.
- Place vertices across the slope, or type coordinates in the command input.
- Click Done Weak Layer.
A weak layer requires at least 2 points. The polyline is clipped to the model geometry, so you can extend it past the boundary without affecting the analysis.
Use Clear Weak Layers to remove all weak layers.
Material
Each weak layer carries its own material, independent of the surrounding regions. Assign it from the Material Strength control in the properties pane for the selected weak layer. The weak layer can use any of the supported failure criteria along its length.
Role in the slip-surface search
When a trial surface runs near a weak layer, the search can force the surface to follow the seam, so the critical surface honors the low-strength path rather than cutting cleanly through stronger material. How weak layers combine with other surfaces during the search — and the rules for combining multiple seams — is documented separately.
Search behavior
The detailed rules for how the search forces surfaces onto weak layers and combines them are covered in Weak Layer Handling.