Based on PFC Simulation, a Study on the Crack Development Characteristics of Drilled Coal Samples under Uniaxial Compression

Li Peng, Zhao Mingyi, Jin Xiaohua, Kou Mengnan, Xu Yang

Zhongyuan University of Technology, School of Smart Energy and Environment

Abstract：

To investigate the initiation, propagation, and breakthrough mechanisms of internal fractures in coal samples from boreholes during uniaxial compression, this study focuses on coal samples from boreholes in western Henan. By employing in-situ uniaxial compression testing combined with high-resolution CT scanning, CT cross-sectional images and stress-strain curves were obtained throughout the entire loading phase; Combining Avizo 3D reconstruction with PFC2D discrete element numerical simulation, an integrated research framework of “macroscopic mechanical response—microscopic structural evolution—numerical validation” was established. The results indicate that the stress-strain curve exhibits a typical “S”-shape and can be divided into four stages: consolidation (0-0.5%), linear elasticity (0.5%-1.2%), yield (1.2%-2.0%), and post-peak (＞2.0%); The simulation results show excellent agreement with the experimental curves in terms of the nonlinear characteristics of the consolidation stage, the linear elastic modulus (0.65–0.70 GPa), and the peak strength (relative error of 3.5%). The fracture angle significantly influences the failure mode: when the pre-existing fracture angle is 45°, shear slip dominates, resulting in the greatest strength reduction (approximately 36%); when the pre-existing fracture inclination is 90°, tensile failure dominates, with a 28% reduction; and when the pre-existing fracture inclination is 135°, a combined tensile-shear failure mode occurs, resulting in a 22% reduction. Due to their non-through nature and randomness, natural fracture networks exhibit distributed progressive damage characteristics, manifested as continuous strain hardening and sawtooth fluctuations, which effectively delay the formation of macroscopic fracture surfaces. This study verifies the reliability of the PFC2D model in simulating the uniaxial compressive mechanical behavior of coal and rock, reveals the control mechanism of fracture geometry and topology on instability pathways, and provides a theoretical basis for modeling the damage behavior of coal and rock as well as for early warning of dynamic disasters.

Key Words：

borehole coal samples; uniaxial compression; 3D reconstruction; PFC discrete element simulation