Engineering Rock Mechanics

72 Strain

Figure 5.1 Large displacements around an originally arch-shaped coal mine access

tunnel (from Pan, 1989).

grasp the concept of normal strain than shear strain. This is because the
normal displacement and the associated strain occur along one axis.
However, in the case of shear strain, the quantity of strain in say, the
x-direction, also depends on the position along the y-axis. In other words,
normal strain only involves one Cartesian axis, whereas, shear strain
involves two (or three), i.e. it involves an interaction between the axes.
One convenient simplification that can be introduced to aid the study
of strain is the concept of homogeneous strain which occurs when the state

Figure 5.2 Example of the evolution of a complex displacement field (from Ramsey
and Huber, 1983).