Modeling of the Brazilian Tensile Test on Transversely Anisotropic Rocks using PDEM

A new numerical approach based on the particle discrete element method (PDEM) is put forward to investigate the mechanical behavior of transversely isotropic rocks with non-continuous planar fabrics. In this numerical model, the rock matrix and fabric are represented as flat joint contacts and smooth joint contacts, respectively. The following are studied using the numerical model: (1) the effects of the micro-structure of the rock matrix and the fabric micro-parameters on the shear strength and the fracture patterns of rocks under Brazilian tests, and (2) the model calibration process for determining the micro-parameters and the failure process of borehole stability in layered rock. The results show that: (1) Based on the Brazilian test results of 20 kinds of transversely isotropic rocks with non-continuous planar fabrics, six patterns regarding the relationship between the normalized failure strength (NFS) and fabric-loading angles are obtained; (2) The patterns of NFS curves are slightly affected by the coordination numbers of particle in rock matrix, while greatly affected by the amount of pre-existing micro-cracks in rock matrix, and the stiffness, strength and distributed region of the fabrics; (3) The calibrated results of six typical rocks with different patterns agreed well with the experimental results in regard to failure strength and fracture patterns; (4) The fracture of layered surrounding rock after borehole excavation is concentrated in two zones with the line connecting the center of the two zones is normal to the plane of non-continuous fabrics for isotropic geo-stress field, while the connecting line is deflected to the direction of minor principal stress to a certain extent for non-isotropic geo-stress field.