Experimental and numerical investigation on the mechanical characteristics and failure mechanism of cracked coal & rock-like combined sample under uniaxial compression

Abstract

The coal and rock bear the load together considering the fact that underground mining is usually operated in layered beds, which results in that the mechanical responses of the coal-rock combined body (CRCB) are distinct from those of pure coal or rock mass. However, the engineering structure of CRCB is mostly in a state of crack development, and therefore it is necessary to investigate the mechanical behavior and failure mechanism of CCRB containing cracks for assessing structural safety and disaster prevention. In this paper, a series of uniaxial compression tests were carried out on cracked coal-rock combined (CCRC) samples, and the strength and deformation characteristics, acoustic emission (AE) features and failure process of samples with various crack inclination angles were analyzed. Based on the stress state of coal and rock section near the interface, the constraint effect was founded and the variation of strength characteristics for the materials on both sides of the interface was discussed. Furthermore, a failure criterion was proposed to predict whether cracks would penetrate the interface, and the results of theoretical analysis agree well with the failure characteristics of the CCRC samples observed in the test. Then a numerical model was developed in PFC2D and its accuracy was verified. The failure pattern is further numerically investigated and the failure criterion is verified again based on the simulated micro-crack evolution behavior near the interface. Besides, the mechanical characteristics and failure features of CCRC sample with respect to different crack lengths, positions and inclination angles are also studied, which helps understand the mechanical behaviors and failure characteristics of CCRB structure more comprehensively.