Experimental and Numerical Study of Phyllite’s Anisotropic Behavior in 3D Space Under Brazilian Test Conditions

Phyllite is a kind of typical anisotropic rocks with well-developed foliations. This article aims to study the influence of foliations on the mechanical behaviors of phyllite in three-dimensional (3D) space under Brazilian test conditions. First, the overall behaviors of various anisotropic rocks in 3D space were summarized based on statistical analysis. Then, the acoustic emission signals were investigated in detail to study the micro-fracture process of phyllite. Finally, a new numerical model considering the crystal structures and weak structural planes of phyllite based on the particle discrete element method (PDEM) was developed. The micro-mechanism behind the macro-phenomenon and the failure process of specimens with different fracture patterns were discussed through numerical simulations. The results show that: (1) based on the Brazilian test results of nine kinds of anisotropic rocks in 3D space, the patterns regarding the relationship between the normalized failure strength (NFS) or anisotropic index and fabric-loading angles or orientation angles are obtained; (2) The failure strength of specimens, the temporal distributions of the AE counts and AE energy were closely related to their fracture patterns and the areas of their fracture surfaces. In addition, nine macro-fracture patterns and two distribution patterns of AE signals were obtained; (3) The distribution of micro-cracks has evident accumulation features due to the effect of foliations and the proportions of shear cracks and tensile cracks are influenced by the loading-foliation angles and inclination angles; (4) The calibrated results of phyllite agreed well with the experimental results with regards to failure strength and fracture patterns. During failure process, the intra-grain cracks and inter-grain cracks mainly occurred at the plastic loading stages, and shear cracks along weak planes dominated.