TABLE OF CONTENTS Strain is a change in the relative configuration of points within a solid. One can study finite strain or infinitesimal strain both are relevant to the deformations that occur in the context of the principles of rock mechanics and their engineering applications. Large-scale strain can be experienced underground as illustrated in Fig. 5.1, where there is severe deformation around a coal mine access tunnel. When such displacements are very small, one can utilize the concept of infinitesimal strain and develop a strain tensor directly analogous to the stress tensor. Thus, we will first discuss finite strain and then infinitesimal strain.
Strain may be regarded as normalized displacement. If a structure is subjected to a stress state, it will deform. However, the magnitude of the deformation is dependent on the size of the structure as well as the magnitude of the applied stresses. In order to render the deformation as a scale-independent parameter, the concept of strain (which in its simplest form is the ratio of displacement to the undeformed length) is utilized. Such displacements can also occur naturally in rock masses through the application of tectonic stresses resulting from past and present geological processes. Some excellent examples are shown in Ramsey and Huber (1983).
The displacements, whether natural or artificial, can be complex; an example is shown schematically in Fig. 5.2. It should also be noted that strain is a three-dimensional phenomenon that...
