Abstract
Due to differences in the properties of coal and gangue, gangue-containing coal often exhibits complex damage characteristics, which has become a key factor limiting the recovery rate in top coal caving. In order to improve the efficiency of top coal caving, it is necessary to recognize the failure mechanism of gangue-containing coal, especially the stress drop mode and the residual bearing capacity. In this paper, the post-peak mechanical properties of gangue-containing coal samples were investigated. With the aid of the PFC2D software, a model of gangue distribution in different layers of gangue-containing coal samples was established by changing the bonding properties of the balls in different layers, and triaxial numerical simulation experiments were carried out under different confining pressures. According to the Mohr–Coulomb failure criterion, a post-peak stress–strain model based on equivalent plastic strain was proposed for gangue-containing coal. The results show that the theoretical values are in good agreement with the numerical simulation values. The strength is mainly affected by the cohesive force during the first stress drop, and the effect of the internal friction angle on the strength cannot be neglected during the second stress drop. Furthermore, the brittleness characteristics of gangue-containing coal are studied. It is found that the brittleness drops rapidly when the confining pressure rises from 5 to 10 MPa, and the position of gangue has a significant impact on the softening coefficient. Finally, the quantitative relationship between the brittleness and the burst proneness was established from the perspective of energy, and the brittleness was partitioned according to the burst proneness. The research findings are beneficial for improving the recovery rate and identifying the burst proneness of coal seams to ensure safe and efficient production.
Highlights
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The first and second stress drops are affected by the cohesion C and the internal friction angle, respectively.
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The position of gangue has a significant impact on the softening coefficient.
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The quantitative relationship between the brittleness and the burst proneness was established from the perspective of energy.
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The research described in this paper was financially supported by the Fundamental Research Funds for the Central Universities (2017XKZD06).
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Liu, S., Ma, P., Meng, F. et al. Strain softening and brittleness characteristics of gangue-containing coal samples. Geomech. Geophys. Geo-energ. Geo-resour. 7, 28 (2021). https://doi.org/10.1007/s40948-021-00226-9
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DOI: https://doi.org/10.1007/s40948-021-00226-9