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Journal of ZheJiang University (Engineering Science)  2022, Vol. 56 Issue (12): 2445-2453    DOI: 10.3785/j.issn.1008-973X.2022.12.013
    
Strength and fracture characteristics of coal rock disturbed by protective layer mining under graded cyclic loading
Yong-bo YANG1,2(),Zhe ZHOU1,*()
1. State Key Laboratory of Coal Mine Disaster Dynamics and Control, Chongqing University, Chongqing 400044, China
2. Chongqing Research Institute, China Coal Technology and Engineering Group, Chongqing 400037, China
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Abstract  

Aimed the coal rock disturbed by the protective layer mining under the action of repeated mining during the recovery was likely to induce the destabilization problem of the roadway surrounding rock, the graded cyclic loading was adopted to simulate the long-term effects of mining stresses in the actual recovery projects, to investigate the mechanical strength and deformation damage characteristics of coal rock disturbed by protective layer mining under graded cyclic loading. Results show that the volume expansion deformation of the coal samples disturbed by the protective layer mining under the process of loading and unloading is obvious, the internal structure damage degree of the coal samples is higher than that of the coal samples undisturbed by the protective layer mining. In the later stage of loading and unloading, the coal samples disturbed by the protective layer mining show plastic failure, while the coal samples disturbed by the protective layer mining show obvious brittle failure. Compared with the coal samples undisturbed by the protective layer mining, the peak strength of the coal samples disturbed by the protective layer mining decreases, the fracture volume of the coal samples per unit volume (50 mm diameter and 100 mm height) increases significantly, and both the peak intensity and fracture volume ratio are distributed more uniformly along the coal seam direction. The physical properties of the coal samples undisturbed by the protective layer mining in the fault zone differ greatly from each other. The coal samples disturbed by protective layer mining is more in line with the law of “there is an inverse corresponding distribution between the complexity of coal rock fractures and the peak strength when coal rock is destroyed” than that of coal samples undisturbed by protective layer mining.



Key wordsmining disturbance      cyclic loading      peak strength      fracture reconstruction      fracture distribution      three-dimensional fracture fractal dimension     
Received: 08 January 2022      Published: 03 January 2023
CLC:  TD 18  
Fund:  国家自然科学基金资助项目(51625401,51774055);中国平煤神马集团焦煤开发与综合利用国家重点实验室开放研究基金资助项目(41040220171106-1)
Corresponding Authors: Zhe ZHOU     E-mail: yangyongbocqu@163.com;zhouzhe@cqu.edu.cn
Cite this article:

Yong-bo YANG,Zhe ZHOU. Strength and fracture characteristics of coal rock disturbed by protective layer mining under graded cyclic loading. Journal of ZheJiang University (Engineering Science), 2022, 56(12): 2445-2453.

URL:

https://www.zjujournals.com/eng/10.3785/j.issn.1008-973X.2022.12.013     OR     https://www.zjujournals.com/eng/Y2022/V56/I12/2445


分级循环荷载下保护层开采扰动煤岩强度及裂隙特性研究

针对回采时反复采动作用下的保护层开采扰动煤岩极易诱发巷道围岩失稳的问题,采用分级循环荷载模拟实际回采工程中采动应力的长期作用,研究保护层开采扰动煤岩在循环荷载作用下的力学强度及变形破坏特性. 试验结果表明,在加卸载过程中,受保护层开采扰动煤样的体积膨胀变形明显,煤样内部结构破坏程度比未受保护层开采扰动煤样更高. 在加卸载后期,受保护层开采扰动煤样表现为塑性破坏,未受保护层开采扰动煤样发生明显的脆性破坏. 相比于未受保护层开采扰动煤样,受保护层开采扰动煤样的峰值强度下降,单位体积(直径为50 mm,高度为100 mm)内的煤样裂隙体积显著增加,峰值强度和裂隙体积占比均沿煤层走向分布较为均匀. 处于断层带的未受保护层开采扰动煤样的彼此物性差异较大. 受保护层开采扰动煤样比未受保护层开采扰动煤样更符合“煤岩破坏时,裂隙空间复杂程度与峰值强度存在反向对应分布”规律.


关键词: 开采扰动,  循环荷载,  峰值强度,  裂隙重构,  裂隙分布,  三维裂隙分形维数 
Fig.1 Spatial position and samples preparation of Ji14-31050 and Ji15-31030 coal seams
Fig.2 Coal rock mechanical test and fracture scanning equipment
Fig.3 Graded cyclic loading and unloading diagram of coal sample
Fig.4 Deviatoric stress-strain curve of coal samples 255 m from open-off cut
Fig.5 Peak strength distribution of coal in study area
Fig.6 Fracture three-dimensional reconstruction and extraction of coal sample
Fig.7 Calculation of fractal dimension of three-dimensional fracture of coal rock at 255 m from open-off cut
L / m 是否受保护层
开采扰动
拟合线性方程 R2 D
96 $y = - 2.169\;6x+8.349\;6$ 0.9999 2.1696
96 $y=-1.996\;0x+8.119\;7$ 0.9998 1.9960
170 $y = - 2.181\;5x+8.453\;2$ 0.9994 2.1815
170 $y = - 1.916\;5x+7.842\;4$ 0.9987 1.9165
255 $y=-2.215\;2x+8.696\;4$ 0.9993 2.2152
255 $y = - 1.912\;1x+7.823\;8$ 0.9995 1.9121
389 $y = - 2.188\;4x+8.726\;4$ 0.9995 2.1884
389 $y = - 1.953\;6x+8.169\;4$ 0.9999 1.9536
495 $y = - 2.217\;8x+8.683\;9$ 0.9999 2.2178
495 $y = - 1.994\;0x+8.343\;6$ 0.9997 1.9940
640 $y = - 2.442\;8x+8.715\;3$ 0.9999 2.4428
640 $y = - 2.087\;5x+8.540\;3$ 0.9997 2.0875
680 $y = - 2.332\;9x+8.698\;1$ 0.9999 2.3329
680 $y = - 2.045\;2x+8.479\;0$ 0.9996 2.0452
834 $y = - 2.250\;6x+8.660\;7$ 0.9995 2.2506
834 $y = - 1.954\;1x+8.430\;1$ 0.9997 1.9541
Tab.1 Three-dimensional fracture fractal dimension of coal sample
Fig.8 Fracture volume distribution of coal in study area
Fig.9 Corresponding distribution law of three-dimensional fracture fractal dimension and peak strength of coal rock
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