Abstract
Coal mines are composed of multiple complex rock strata with different mechanical characteristics and energy accumulation and release performances. This implies uneven energy distribution in the coal-rock combination system (CRCS). To explore the effect of the included angle between the loading direction and the coal-rock contact surface on the mechanical properties, crack propagation mode, and energy evolution characteristics of the CRCS, the uniaxial compression tests were carried out on the CRCS samples with zero and 30° inclination angles. The obtained mechanical properties and energy dissipation trends of the tested samples were similar to those of the pure (raw) coal and rock ones but strongly depended on the inclination angles. The impact energy index of the CRCS samples was smaller than those of the pure coal and pure rock samples, and its impact tendency was less pronounced. The deformation and failure of the CRCS samples occurred in the coal part, the rock part inhibiting the development and deformation of the coal. According to the deformation and failure characteristics of the CRCS, the coal support far away from the contact surface should be strengthened in engineering practice to avoid the rock mass failure caused by the expansion and evolution of cracks in the coal part. At a 30° inclination angle, the CRCS sample was tensioned at the coal-rock contact surface, and the original cracks and pores were gradually compacted under the stress component perpendicular to the contact surface. With an increase in the inclination angle, the difference between the total energy accumulated before the peak and the released energy after the peak was reduced, and the difference between the total energy accumulated before the peak and the dissipated energy increased gradually. CRCS samples with different inclinations exhibited three damage stages: initial damage, stable damage growth, and rapid damage growth. The results obtained are considered instrumental in rockburst preventing, monitoring, and early warning under different stress environments.
Highlights
As the depth and intensity of coal mining continue to increase, large deformation of the roadway and dynamic disasters become more and more topical [1, 2]
The strength of the coal-rock combination systems (CRCS) samples slightly exceeded that of pure coal monomers, indicating that the strength of the CRCS sample mainly depended on the coal
The peak strain of the CRCS sample is less than that of the pure coal sample and pure rock sample, mainly because the rock mass part of the CRCS sample experienced no significant deformation under the uniaxial compression load [24, 25]
Summary
As the depth and intensity of coal mining continue to increase, large deformation of the roadway and dynamic disasters become more and more topical [1, 2]. The mechanical characteristics, energy evolution, and impact tendency of the CRCS with different combination modes, coal-rock height ratios, strength ratios, and dip angles became topical for the global research community. Zuo et al [7, 8] carried out the strength and deformation failure tests on CRCS with different coal-rock combinations They revealed the effect of different combinations on the impact tendency of the coal-rock system. Chen et al [10] studied the variation trends of mechanical parameters of CRCS with different coal-rock height ratios They analyzed the gradual instability process and failure mode of the coal-rock combination structure. Zhang et al [11] carried out uniaxial and triaxial compression tests on samples of three different coal-rock combinations and analyzed the influence of combination modes on the CRCS mechanical properties and failure modes. The energy accumulation trends in the CRCS were analyzed to provide references for the prevention and monitoring of dynamic disasters in coal mines
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