Anisotropic Nature of Jointed Rock Mass Strength

Analytical models that describe the strength of jointed rock under a wide variety of multiaxial states of stress with one or two components being tensile are presented. The intact rock is. isotropic and its strength is described by a Hoek and Brown criterion. The joints have zero tensile strength and a shear strength defined by a Coulomb criterion. The strength of jointed rock is represented by superposition of the intact rock and joint failure surfaces and the joint nonnegative normal stress condition in a coordinate system having two stress ratios as a measure of distance along the coordinate axes. The symmetry of the intact rock failure surface in this coordinate system is lost because of the directional nature of joint strength. The anisotropic strength reduction associated with the joints and the influence of the intermediate stress on the strength of regularly jointed rock are analyzed. The effect of water pressure on jointed rock strength is also addressed.