Modeling of Independent Versus Dependent Tensile–Frictional Strength Behavior of Jointed Rocks

Abstract

The failure mechanisms of non-persistent jointed rocks are crucial in understanding rock mass behaviour. This paper investigates the relationship between the tensile and frictional strength of jointed rock samples numerically and compares that with the results of previous laboratory-tested samples using two strength criteria. The first criterion assumes that tensile failure reduces shear strength parameters to their residual values, which is dependent behavior (Model 1). The second criterion assumes that tensile failure will not cause the shear strength parameters to be reduced to their residual values, which is independent behavior (Model 2). This numerical model uses the Mohr–Coulomb criterion with cohesion, friction, and tensile strength cut-off parameters, as tested in the laboratory. These artificial rock samples contain open joints with the same inclination but with different bridge inclinations of 45°, 60°, and 75°. The samples were tested in the laboratory until failure while monitoring displacement and rupture development. As the stress concentration increased, curvilinear yielding (wing crack) started near or at the joint tips and propagated and stopped or coalesced to form a continuous rupture surface. The numerical model showed that tensile stress caused wing crack initiation due to stress flow around the open joints. When using Model 2 as compared to Model 1, there was a strong and significant agreement between the laboratory tests and the numerical models in terms of the yielding path, width of the failure zone, and the uniaxial strength. The results indicate that tensile yielding should not affect the shear strength parameters.

Keywords: Friction, Tensile strength, Non-persistent joint, Independent Friction-Tensile, Tension yielding