Preferred Orientation, Symmetry Concepts and Strength Anisotropy of Some Rocks and Clays

Abstract

There is quite a close conceptual and analytical affinity between, on the one hand, the orientation distribution of microscopic planar and near-planar elements in a rock and clay, and on the other hand the distribution of larger-scale discontinuities in weaker rocks such as shales and mudstones and even in stiff clays such as the London Clay. The analysis of larger-scale ‘field’ discontinuities, together with the manner in which they impose a control on mass strength of the rock is considered in Chapter 6. In the present chapter, the intention is to introduce the idea of crystallographic preferred orientation in polymineralic aggregates and to consider the influence of such orientation density distributions upon intact strength. Intact strength anisotropy may be much more directly related to planar element distributions in a homogeneous material than it will be in a material that is also inhomogeneous.