An investigation into the tensile behaviour of a schistose rock

Abstract

An experimental investigation was conducted into the behaviour of a quartzitic gneiss in a direct tensile test. It was found that the stress-strain relation is quasi-linear up to failure, which occurs in a brittle way. The values of the stiffness modulus and of the apparent tensile strength are dependent on the inclination of the schistosity with respect to the loading direction. It is shown that the behaviour prior to failure can be modelled by a linear elastic anisotropic constitutive law. To describe the variation of strength with the schistosity inclination, a theory is formulated that allows the observed data to be reproduced and the inclination of the failure plane to be predicted. Predictions show an overall agreement with observed data. However, for schistosity inclination close to the loading direction, the theory overpredicts the experimental results. It is suggested that a different mechanism may be the cause of failure in such cases. Finally, for use in the solution of boundary value problems, the extension of the strength criterion to full 3-D loading conditions is formally given.