Numerical Modeling of Independent versus Dependent Tensile -Frictional Strength Behavior of Synthetic Rocks with Non-continuous joints

The failure mechanisms of non-continuous jointed rocks under compression loading is of great importance for the rock mechanics community; it plays an important role in understanding the fracturing pattern, the type of the fractures, and the strength of the rock mass under investigation. In this paper, the relationship between the tensile and frictional strength of jointed rock samples is investigated by numerical modeling. Previously tested samples were used to simulate the behavior of artificial jointed rock numerically under axial loading by using two strength criteria; the first assumes that tensile failure reduces shear strength parameters to their residual values (dependent behavior, Model 1) and the second assumes that tensile failure will not cause the shear strength parameters to be reduced to their residual values (independent behavior, Model 2). The numerical model, in this paper uses, Mohr-Coulomb shear strength criterion with parameters of cohesion, friction, and tensile strength cut-off as tested in the laboratory. These artificial rock samples contains open-joints with the same inclination but with different bridge’s inclinations of 45°, 60°, and 75°. These samples were tested in the laboratory under incremental uniaxial loading until failure while monitoring displacement and rupturing 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 concentration caused wing crack initiation due to stress flow around the pre-existing non-persistent open joints. The yielding behavior of the numerical simulations - under the two tensile strength failure criteria - and the laboratory tests shows good agreement for the three samples. However, when the shear strength and tensile strength parameters are independent, the results showed strong and significant agreement between the laboratory tests and the numerical models in terms of the yielding path, width of failure zone, and the uniaxial strength. In this all compressive load environment, stress flow caused tensile stress concentration near the joint tip and according to the results of this paper the tensile yielding should not force the shear strength parameters to go to their residual values.