Static and dynamic uniaxial compression tests on coal rock considering the bedding directivity

The mechanical properties and behavior of coal rock under both static and dynamic loading rates are of importance in the coal mining practices. In this study, both quasi-static and dynamic uniaxial compression tests are conducted on coal rock, considering the bedding directivity of coal rocks using a MTS hydraulic servo-control testing machine and split Hopkinson pressure bar (SHPB), respectively. The attained strain rates range from 10(-5) to 10(-2) s(-1) for static tests and 20 to 100 s(-1) for dynamic SHPB tests. For dynamic tests, pulse-shaping technique is utilized to achieve dynamic force balance and thus validate the quasi-static data reduction. A high-speed camera is used to capture the failure process in SHPB tests. The characteristics of failure mode, fracture strength, energy dissipation, and fractal dimension are investigated. A significant strain-rate-dependent behavior of coal rock is revealed, and the compressive strength, elasticity modulus and energy consumption increase with increasing strain rate. The bedding effect on the coal behavior at static strain rate is more prominent than that at dynamic strain rate. The measured strengths along different bedding directions exhibit distinct variations, featuring significant anisotropy. In addition, a sieving statistics analysis of the recovered fragments depicts obvious fractal; and the fracture dimension can be correlated to the fractal energy dissipation.