Rock ‘elasticity’ at high pressures

Abstract

The determination of the elastic moduli arises in conjunction with the formulation of inelastic constitutive equations for rock-like materials if, as well as other properties, the rock also exhibits elastic properties. It has been mentioned in previous chapters that various authors have suggested that the elastic moduli have to be determined from the initial slopes of the stress—strain diagrams, assuming, by analogy with the behaviour of metals, that at relatively small stresses the behaviour of the rock is linearly elastic. However, as it has already been emphasized, the experimental evidence shows that even at relatively small stresses which produce small but non-negligible strains, the behaviour of the rock is not linearly elastic, but is in fact time-dependent. Thus, any method of determining the elastic moduli from the slopes of various portions of the stress—strain curves obtained during loading will not, strictly speaking, determine proper elastic moduli. With such a procedure, at best, a linearized version of the stress—strain relation is obtained for loading processes. Such a linearization is sometimes used for practical purposes, in order to make it possible to utilize simple strength-of-materials formulae.