Numerical Modeling of Failure Mechanism of Transversely Isotopic Under Triaxial Loading By Discrete Element Method

Summary
Anisotropy is an important feature of sedimentary and metamorphic rocks. This character affects opening stability and must be considered in design. So many laboratory tests are done to consider the influence of anisotropy on mechanical behavior and failure strength of such rocks.
 
Introduction
Numerical modeling is an effective tool in design of structures and stability analyses. Because of computational complexity and the difficulty of determining the necessary elastic constants, it is usual for only the simplest form of anisotropy, transverse isotropy, to be used in design analyses. The peak strengths developed by transversely isotropic rocks in triaxial compression vary with the orientation of the plane of isotropy, foliation plane or plane of weakness, with respect to the principal stress directions.
 
Methodology and Approaches
In this study the behavior of a transversely isotropic rock under triaxial loading is considered by using distinct element method due to its potential to modeling failure process of anisotropic materials and because of its ability to monitoring failure of these rocks under uniaxial and triaxial conditions. The bonded-particle discrete element method with embedded smooth joints was applied to model the mechanical behavior of transversely isotropic rock with systematic verifications. Particle Flow Code 2D (PFC2D) developed by Itasca was applied in this study to employ the bonded-particle DEM. The bonded particle model was adopted to construct isotropic rock without weak planes, which was calibrated based on elastic modulus and strengths that have the least effect of weak planes. Then, the smooth joint model was inserted to create the weak cohesive planes to simulate the behavior of the equivalent anisotropic continuum.
 
Results and Conclusions
The results showed that the bonded-particle DEM model with embedded smooth joints was able to simulate the transversely isotropic rock. In this Research, some samples made by PFC were loaded under confining pressure in varying layering angle (0 to 90). Results showed that the distinct element method is able to model transversely isotropy and is in a good accordance with experimental data. Also it’s indicated that the peak strength of transversely isotropic rock is related to angle of anisotropy and its variation versus to layering angle show U-shape curves with unequal shoulder which has a minimum value in 30 degree of layering and a maximum value in zero. Results indicated that increase of confining pressure doesn’t change the failure mode of transversely isotropic rocks, unevenness ratio and depth ration. This study pave the way for further applications, and the bonded-particle DEM model can be further employed effectively in rock engineering applications, particularly in transversely isotropic rock formations.