Experimental Study and Numerical Simulation of the Dynamic Behavior of Transversely Isotropic Phyllite

Understanding the dynamic mechanical behavior of transversely isotropic rocks is essential in various fields of rock engineering, such as tunnel digging, blasting, and underground excavation. The bedding structure and strain rate determine the failure features of transversely isotropic rocks. Dynamic compression tests of transversely isotropic phyllites with different bedding angles were carried out using the split Hopkinson pressure bar (SHPB) approach to study the dynamic mechanical properties of transversely isotropic rocks. The resulting failure modes were characterized as two types (class I and class II) to describe the deformation behavior and fracture patterns under different strain rates. Both the strain rate and bedding angle influence the dynamic compressive strength. The dynamic compressive strength changes in a U-shaped trend as the bedding angle increases under similar strain rates. This trend becomes more pronounced as the strain rate increases. The failure patterns of the specimens tested under different strain rates are diverse. To gain a better understanding of the dynamic compressive behavior of phyllite, the discrete element method (DEM) was utilized to reveal the microfracture mechanism and failure process under extreme loads with the help of SHPB testing. The validity of the numerical simulation was verified by comparing the numerical results with the laboratory results. The thresholds dividing class I and class II failure for different bedding angles were investigated by applying different impact velocities. A scaling law was proposed to describe the increase in the dynamic strength of transversely isotropic phyllites. In addition, the microcrack propagation and microcrack type were analyzed to explore the influence of the bedding structures on the failure pattern and compressive strength. Different failure patterns form from different microcrack propagation processes, and the resistance of microcrack generation determines the strength of phyllites with different bedding angles. (c) 2020 American Society of Civil Engineers.