A mechanical equation of state for brittle rock: Part II—The prefailure initiation behavior of brittle rock

Abstract

Results are presented of a theoretical and experimental study of the mechanical behavior of brittle rock within the pre-failure initiation region. The pre-failure initiation region includes regions I and II behavior and is defined to represent the behavior of rock where no noticeable crack growth has occured within the rock; that is, where there is no measurable deviation of the stress-volumetric strain curve from linearity during region II. Thus, we consider only the influence of open and closed cracks initially present within the rock on the overall behavior of the rock. It is shown that the constitutive relationships of brittle rock in the pre-failure initiation region can be described by six equations relating the three pricipal stresses and principal strains resulting from closure of open cracks (‘op’ deformation mode) and frictional sliding along suitably orientated closed cracks (‘cls’ deformation mode). Experimental data for Westerly granite deformed under uniaxial, triaxial, and biaxial loading is used to check the theoretical model. The results of these tests indicate that for engineering purposes, the behavior of rock under multiaxial loading can be predicted accurately once the behavior of the rock under uniaxial and triaxial loading has been determined. Interpretation of these results further suggests that a continuum approach to predicting the mechanical behavior of rock may be justified.