TABLE OF CONTENTS Stress is a concept which is fundamental to rock mechanics principles and applications. For those encountering stress for the first time, it is not a straightforward concept to grasp unless explained very clearly. For this reason, and at this stage in the book, we have adopted a key point approach to explaining the concept of stress. This is a direct precursor to Chapter 4 on in situ stress and provides a link with strain in Chapter 5. Further explanation of stress is given in Appendix A.
There are three basic reasons for an engineer to understand stress in the context of rock mechanics. These are:
There is a pre-existing stress state in the ground and we need to understand it, both directly and as the stress state applies to analysis and design. This has been discussed in Chapter 2 in the context of the geological setting. It is emphasized again here that there can be circumstances when, during the engineering, no new loading is applied, e.g. when driving an unsupported tunnel in rock. In this latter case, the pre-existing stresses are redistributed which leads us to the next reason.
When engineering occurs, the stress state can be changed dramatically. This is because rock, which previously contained stresses, has been removed and the loads have to be taken up elsewhere. In line with this fact, it is also noted in Section 3.9 that all unsupported excavation surfaces are principal stress planes, a...
