School of Mechanics and Engineering, Liaoning Technical University
Liaoning Key Laboratory of Mining Environment andDisaster Mechanics, Liaoning Technical University
State Key Laboratory Cultivation Base for Gas Geology and Gas Control
School of Environment, Liaoning University

新掘未支护或回采工作面前方巷道受开采扰动具有沿垂向急剧升高而径向迅速降低的典型受载特点,而更易失稳、诱发冲击地压事故,深入研究采动卸荷下含瓦斯煤岩力学特性及伴随出现的声发射信号规律,是揭示深部高瓦斯煤层冲击地压发生机理并形成科学、有效的预警体系的基础。运用物理实验方法,基于自主研发的含瓦斯煤岩真三轴测试系统,开展垂向加荷–径向单面卸荷路径下含瓦斯煤岩受载实验,并监测全历程出现的声发射信号,分析卸荷速率、瓦斯压力对煤岩力学特性及声发射信号影响规律,引入统计分形理论开展煤岩碎块分布筛分统计,结果表明:单面卸荷路径下含瓦斯煤岩应力–应变关系具有弹性、非线性增长和软化的典型 3 阶段特征,高卸荷速率和瓦斯压力,降低了煤岩强度、峰值应变量,但使峰后阶段应力降模量增大,而随着初始围压升高使得该特征呈反向变化。试样破坏后表现为由卸荷面指向内部的典型多剪切带与层状块体交替出现的“洋葱皮”式破坏形式,且卸荷速率越高,形成的贯穿裂隙越多、剪切带内糜棱状粉末减少而碎块尺度增大,相应的统计分形维数越低,而较高的初始围压和瓦斯压力使煤岩塑性特征增加而分形维数升高。三向应力状态与瓦斯的存在使煤岩受载具有塑性特点而伴随出现的声发射信号更加密集、连续,单面卸荷形成的渐进性破坏过程导致声发射具有明显的信号激增现象和最高值脉冲信号出现,次高值信号产生于应力峰值,随卸荷速率、瓦斯压力升高,两高值信号幅值增加且最值信号出现提前,声发射能量累计量“阶梯”增长现象愈发明显但累计总量逐渐降低。高瓦斯压力、初始围压及卸荷速率使煤岩破坏后具有更多盈余能,在实际工程中,高瓦斯压力、地应力使新掘巷道或支护失效围岩径向应力迅速降低并发生渐进性破坏而形成断续结构,易受高静载或冲击扰动致整体结构失效,且该部分“富能”围岩会在盈余能推动下发生块体弹射、倾出而形成动力灾害。

The roadway in front of newly excavated unsupported areas or mine working face is more susceptible to mining disturbance, and shows the typical stress characteristics that the load increases sharply in the vertical direction and decreases rapidly in the radial direction, which is more likely to lose its stability and induces rockburst accidents. Studyingthe mechanical characteristics of gas-bearing coal under mining unloading and the accompanying AE signal distribution indepth is the basis for revealing the mechanism of rockburst in deep high gas coal seams and forming a scientific and effective early-warning system. In this paper, the gas-bearing coal loading experiment is carried out under the vertical loading-radial single-sided unloading path, and the AE signals that occur throughout the process are monitored, the influenceof unloading rate and gas pressure on the mechanical properties of coal and the law of AE signals are analyzed, and thestatistical fractal theory is introduced to carry out the screening statistics of coal fragments distribution, which is based onthe physical experimental results by using a true triaxial test system self-developed for gas-bearing coal. The results showthat the stress-strain relationship of gas-bearing coal under the single-side unloading path has a typical characteristic ofthree stages, that is, elasticity, nonlinear growth and softening. There is a lower strength and strain at peak of coal, affected by a larger unloading rates and gas pressure, but an increasing modulus of stress reduction in the post-peak stage,while increasing the initial confining pressure has the opposite effect. There are typical multi-shear bands and layeredblocks appearing alternately from the unloading surface to the interior, namely the “onion skin” failure forms of coal. Thehigher unloading rate is, the more penetrating cracks develop. The mylonitic powder in the shear zone decreases and thefragment size increases and the corresponding statistical fractal dimension decreases. Meanwhile, there are obvious plasticproperties of coal and a larger fractal dimension, with the higher initial circumferential pressure and gas pressure increase.More plastic characteristics of coal is shown for the three-dimensional stress state and the existence of gas, and the AE signal as a dense and continuous pulse fluctuation accompanies appearance, and there is a clear signal spike with the appearance of the highest pulse signal in the progressive failure process formed by the one-sided unloading phase. The secondhigh value signal is formed with the stress to the peak. As the unloading rate and gas pressure increase, the amplitude ofthe two signatures rises, and the maximum value signal emerges earlier, while the total amount of signal is steadily declining, the “step” increase in the cumulative amount of AE energy is becoming more and more apparent. There is more surplus energy in coal after failure with a higher beginning pressure, gas pressure, and unloading rate. In actual engineering,the radial stress quickly decreases as a result of high gas pressure and ground stress distributed in the surrounding rock ofthe newly excavated roadway or the support’s failure, resulting in progressive damage and the formation of discontinuousstructures. This causes high static loads or burst disturbances, leading to overall structural failure, and dynamic disasterssuch as block ejection and tilting out, driven by surplus energy, are more likely to occur in the “energy-rich” parts of thesurrounding rock.

国家重点研发计划资助项目(2022YFC3004605);国家自然科学基金资助项目(52204218);河南省瓦斯地质与瓦斯治理重点实验室——省部共建国家重点实验室培育基地开放基金联合资助项目(WS2022B08)

丁鑫,高梓瑞,肖晓春,等. 单面卸荷路径下含瓦斯煤岩力学特性与声发射试验研究[J]. 煤炭学报,2023,48(5):2194−2206.

DING Xin, GAO Zirui, XIAO Xiaochun, et al. Experimental study on mechanical properties and acousticemission of gas bearing coal under single surface unloading path[J]. Journal of China Coal Society,2023,48(5):2194−2206.