Stress and time‐dependent failure of brittle rocks under compression: A theoretical prediction

Abstract

A micromechanics‐based continuum theory called interaction field theory (IFT) can reproduce localization phenomena such as shear faulting and axial splitting of rock under compression. The validity of IFT is examined by comparing its predictions of short‐term strength and creep behavior of hard rock with reported experimental data. The theory is formulated through an averaging scheme for an elastic solid containing many microcracks. The growth of the microcracks is assumed to occur through two mechanisms: stress‐induced crack growth and stress corrosion. Failure of rock under compression is known to be governed by the interactive behavior of microcracks. Yet in many earlier analyses the information on interaction is lost through conventional averaging schemes. IFT introduces a new field quantity which represents the interaction effect and the associated governing integral equation. IFT reproduces not only inelastic deformation of rock but also eventual macroscopic failure due to localization of microcracking. In the numerical analysis of short‐term behavior, macroscopic failure is reproduced as a bifurcation from a homogeneous state of deformation into a localized one. The strengths are obtained as a result of numerical analysis with material constants of an intact matrix and the quantities related to initial defects. The strengths of Westerly granite obtained as a function of the confining pressure are compared with published experimental data. For time‐dependent behavior of hard rock, creep tests of granite are analyzed. Comparisons are made between experimental failure times and numerical results for different confining pressures and environmental conditions.