Structural and kinematic analysis

It is very important to consider structures in bedrock when assessing the overall stability of a mountain. This type of data is particularly used for assessment of unstable rock slopes that can lead to rock avalanches; however, they are also suitable for local analysis of smaller rockfalls and rock slides.

Figure: Outcrop with several vertical fractures and a well-developed, shallow dipping foliation.  (Photo: T. Oppikofer, NGU)

Natural discontinuities in bedrock include metamorphic foliation, cracks, fractures and faults. The orientation of the fracturing is measured in the field using a compass, or by using remote measurements based on high resolution digital elevation models (DEM) and appropriate software tools (e.g. Coltop3D). The structural pattern formed by these discontinuities affects the stability of the mountain, which initially can be assessed using simple kinematic analyses. Such an analysis provides information about the existence of structures that can contribute to the possible movement of an unstable block, and what type of failure might occur (planar sliding, wedge sliding and/or toppling). When mapping unstable rock slopes, NGU generally used the standard criteria of rock mechanics with a few adjustments applicable to unstable rock slopes. See NGU report 2012.029.

Kinematiske analyser for ulike mulige bevegelsestyper: a) planutglidning, b) kileutglidning og c) utveltning (Figur fra NGU rapport 2012.029)
Kinematic analysis for various possible failure mechanisms:
a) planar sliding, b) wedge sliding and c) toppling
(figure from NGU report 2012.029)