A New Three-Dimensional Rock Mass Strength Criterion

A new three-dimensional rock mass strength criterion was developed in this paper by extending an existing rock mass strength criterion. This criterion incorporates the effects of the intermediate principal stress, minimum principal stress and the anisotropy resulting from these stresses acting on the fracture system. In addition, the criterion has the capability of capturing the anisotropic and scale dependent behavior of the jointed rock mass strength by incorporating the effect of fracture geometry through the fracture tensor components. The new criterion was proposed after analyzing 284 numerical modeling results of the poly-axial, triaxial and biaxial compression tests conducted on the jointed rock blocks having one or two joint sets by the PFC3D software. Some of these simulation results were compared with experimental ones to validate the developed PFC3D model that was used for numerical modeling of jointed blocks. In this research to have several samples with the same properties, a synthetic rock material that is made of a mixture of gypsum, sand and water was used. To express the new rock mass strength criterion, it was also necessary to determine the intact rock strengths under the same confining stress combinations mentioned earlier. Therefore, the intact rock was also numerically simulated for all three compression tests and the intact rock strengths were found for 33 different minimum and intermediate principal stress combinations.