Chapter 8: Elastic Behavior
In this chapter we describe how the elastic properties of rock are measured
in the laboratory and provide tables of representative values for different
rock types. However, the need to understand the resistance of rocks to
deformation goes well beyond the accumulation of numbers in handbooks.
To analyze a geological structure one must choose the appropriate boundary-
or initial-value problem to serve as a mechanical model, and one must
postulate a particular mechanical behavior. That is, one must say exactly
what the relationship is between the stress acting within a material and
the strain or rate of deformation. These relationships are called constitutive
equations. For example, Hytch et al. (2003), studying the displacement
field around an edge dislocation in silicon as revealed by electron microscopy
(see above), postulated an anisotropic linear elastic constitutive law
and calculated model displacements, ux and uy, that are remarkably similar
to those observed in the laboratory experiment.