Fracture usually crosses column with one loading step, followed by gradual compression of the layer with subsequent loading steps.
Planar or mostly planar fracture that requires more than one loading step to cross column and/or black does not slide easily* on weak layer.
Planar fracture suddenly crosses column with one loading step and the block slides easily* on weak layers.
Fracture suddenly crosses column with one loading step and causes noticeable slope normal displacement.
Irregular fracture surface.
* Block slides off column on steep slopes. On low angles slopes, hold sides of block and note resistance to sliding by gently pulling.
- Fracture Characteristics in Compression Tests by Alec van Herwijnen and Bruce Jamieson
- Interpreting Fracture Character in Stability Tests by Alec van Herwijnen and Bruce Jamieson
- VIDEO: Fracture Character in Compression Tests by Bruce Jamieson
Persistent Weak Layers
- A Winter of Learning: Blog post from February 5, 2014