Jointing
Igneous Joints
Fault Structures
Outline
Joints are discontinuities on which there has been little or no displacement
in shear (in contrast to faults). Joints are ubiquitous in igneous,
metamorphic and sedimentary rocks. They are evidence of brittle failure of
the rock mass at some stage in the deformation history.
Joints have many important properties as planes of weakness in rock masses:
Orientation
- strike and dip or dip and dip-direction.
Spacing
- the frequency or number of discontinuities per unit length.
Aperture
- the mean distance between wall rock surfaces.
Persistence
- the continuity of joints or trace length.
Surface Roughness
- the property controlling friction between surfaces.
Infill
- the presence or absence of breccia, gouge or surface coatings of minerals.
Joints and other discontinuities such as faults, cleavage, metamorphic foliation,
and bedding planes control many important properties of rock masses including:
Strength
Compressibility
Permeability
Igneous Joints
Fault Structures
Outline
(c) Department of Civil and Geological Engineering, University of Saskatchewan,
57 Campus Drive, Saskatoon, SK, Canada, S7N 5A9