TABLE OF CONTENTS In this chapter, we will be describing why a knowledge of in situ rock stress is important for rock engineering, how the in situ stress data are determined and presented, what we would expect the in situ stresses to be, collating stress state data from around the world, and finally commenting on rock stress variability.
The basic motivations for in situ stress determination are two-fold.
To have a basic knowledge of the stress state for engineering, e.g. in what direction and with what magnitude is the major principal stress acting? What stress effects are we defending ourselves and our structures against? In what direction is the rock most likely to break? All other things being equal, in what direction will the groundwater flow? Even for such basic and direct engineering questions, a knowledge of the stress state is essential.
To have a specific and "formal" knowledge of the boundary conditions for stress analyses conducted in the design phase of rock engineering projects.
We have already emphasized that there are many cases in rock engineering where the stresses are not applied as such; rather, the stress state is altered by the engineering activities, e.g. in the case of excavating a rock slope or tunnel.
The stress state at a given point in a rock mass is generally presented in terms of the magnitude and orientation of the principal stresses (remember that...
