TABLE OF CONTENTS We have already emphasized the natural history of the rock material which is being used for engineering purposes. A consequence of the millions of years of mechanical, chemical and thermal processes to which the rock mass has been subjected is that it may well be anisotropic and inhomo-geneous. In this chapter, we will first define these two terms in the context of rock engineering and then explain two useful acronyms, CHILE and DIANE, representing respectively the assumptions required for modelling, as opposed to the actual rock properties. We then discuss the concepts of anisotropy and inhomogeneity, and conclude with a section on the ramifications of the ideas for rock engineering analysis and design.
An anisotropic rock has different properties in different directions. These properties may be of any type: for example, deformability modulus, strength, brittleness, permeability and discontinuity frequency. In some cases, the ability to deal with anisotropy is built into the fundamental definition of the property itself, e.g. the compliance matrix for intact rock can contain up to 21 elastic constants which represent all possible types of elastic anisotropy. In other cases, for example, the compressive strength, there is no such in-built capability and the engineers are left to decide on the optimal characterization of anisotropy commensurate with their requirements. If we measure the compressive strength parallel and perpendicular to the laminations in a metamorphosed rock, is this sufficient to characterize the anisotropic variation?
An inhomogeneous rock has different properties at...
