Environmental Engineering Reference
In-Depth Information
band and bending a soft metal rod. Rock may behave elastically at very low pressures and
temperatures and plastically at higher pressures and temperatures (i.e. at greater depth),
especially if the strain rate or deformation speed is slow, typically changing length at 1
per cent per 10
4
years! Brittle failure, or fracture, occurs if the strain rate exceeds the
plastic deformation rate. Earthquakes occur when this happens abruptly.
Figure 12.20
Principal stresses and their application to
geological structures. Principal stresses operating on the
cube (a) are equal. Cube (b) has been compressed vertically
and has responded by extending in two horizontal planes
whilst conserving its volume. (c) The application of these
forces to a sedimentary rock sequence - which also possesses
lithological fractures.
Source: Partly after Selby (1993).
Figure 12.21
Styles of rock deformation and folding: (a)
stress-strain relationships, (b) the terminology of simple
