Effect of coal strength on the propagation of blasting-induced crack networks across interfaces
GAO Kui1, 2, 3, LI Dianshang1*, REN Bo1, WANG Youwei2, ZENG Qinghui1, #br# YANG Yang1, QIAO Guodong2, ZHANG Xianyue2
(1. State Key Laboratory for Safe Mining of Deep Coal Resources and Environment Protection, Huainan, Anhui 232000, China;
2. School of Safety Science and Engineering, Anhui University of Science and Technology, Huainan, Anhui 232001, China;
3. Key Laboratory of Gas and Fire Control for Coal Mines, Ministry of Education, China University of Mining and Technology,
Xuzhou, Jiangsu 221116, China)
Abstract：The permeability differences between soft and hard coal seams resulting from tectonic evolution are significant. Investigating the dynamic response of coal and roof rock layers with varying strengths during blasting is crucial for optimizing blasting parameters and controlling the surrounding rock in underground roadways. To address the discrepancies in permeability enhancement due to blasting in coals of different strengths, this study employed a combined approach involving model testing, numerical simulation, and field application to examine the attenuation of blasting energy and the damage-fracture characteristics of coal and rock. To quantitatively characterize the damage evolution process within coal, the fractal dimension was introduced to quantify the complexity of the crack network induced by blasting. Based on Weibull theory and the damage probability density function, a quantitative relationship between damage variables and fractal dimension applicable to both hard and soft coal was established, leading to the construction of a blasting damage prediction model based on fractal dimension. The results indicate the following: (1) Blasting in hard coal results in extensive crack propagation, leading to effective permeability enhancement but significant roof damage. In contrast, blasting in soft coal creates a larger crushing zone, resulting in limited permeability enhancement and minimal roof disturbance. Analysis of strain and vibration acceleration data reveals that as the explosive stress wave travels from soft coal across the coal-rock interface into the rock layer, it experiences greater attenuation compared to its travel from hard coal. (2) Damage evolution analysis shows that damage in hard coal appears as striated patterns, while in soft coal, it manifests as regional damage centered around the borehole. Calculations using ImageJ software demonstrate that the fractal dimension of hard coal is greater than that of soft coal at the same time point. The developed damage prediction models for hard and soft coal exhibited high goodness-of-fit, with R² values of 0.96 and 0.94, respectively, confirming the reliability of using fractal dimension for quantitative damage assessment. (3) Based on experimental and numerical simulation results, the charging parameters for blasting permeability enhancement in hard coal seams at Zhaogu No. 2 Mine were designed. Field results indicated that three hours after blasting, the gas drainage concentration increased from 15.33% to 36.74%, and the pure drainage volume rose from 0.085 m³/min to 0.587 m³/min, with no significant damage observed in the roadway roof. These research findings provide a reference and theoretical basis for charge design in blasting permeability enhancement engineering for coals of varying strengths.
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2026, Vol. 45 
