含预制钻孔煤体承载破坏应变场与声发射响应真三轴试验

The true triaxial test of strain field and acoustic emission response of bearing failure of coal with prefabricated borehole

利用具有可视窗口的煤岩真三轴试验系统,开展了含不同孔径预制钻孔的煤体真三轴承载破坏试验,借助数字图像相关(DIC)和声发射(AE)分析方法,研究了煤体承载破坏过程的应变场与声发射响应规律.结果表明:含预制钻孔煤体呈现出拱形破坏裂纹,拱形裂纹区面积、声发射峰值能量及宏观裂纹数量均与孔径呈正相关.煤体承载破坏过程中,孔周煤体逐渐出现应变集中,孔壁发生掉渣、破裂现象,声发射信号开始活跃;随着应变集中程度的加剧,孔壁煤体剥落现象逐渐严重,使孔壁两侧对称出现“V”形破坏区,而“V”形破坏区底部则出现了沿最大主应力方向扩展和延伸的竖向裂纹;当孔周煤体应变集中区域逐步发展为蝴蝶形态时,钻孔上方煤体开始向钻孔空间移动,竖向裂纹则沿最大主应力方向快速扩展并向水平方向偏转,声发射信号急剧增加并达到能量峰值;竖向与水平方向裂纹交汇形成拱形裂纹,而拱形裂纹所包裹的煤体则被分割为独立块体,随后声发射信号明显减弱.

Using the true triaxial test system of coal rock with visible window, the true triaxial bearing failure test of coal with prefabricated borehole of different apertures was carried out. With the help of digital image correlation(DIC) and acoustic emission(AE) analysis methods, the strain field and acoustic emission response of coal in the process of bearing failure were studied. The results show that the coal containing prefabricated borehole presents an arched failure crack, and the area of the arched crack zone, the peak energy of acoustic emission and the number of macro cracks are positively correlated with the pore size. In the process of coal bearing failure, the strain concentration gradually appears in the coal around the hole, the slag and fracture occur in the hole wall, and the acoustic emission signal begins to be active. With the increase of strain concentration, the phenomenon of coal spalling on the hole wall is gradually serious, and the “V” shaped failure zone appears symmetrically on both sides of the hole wall, while the vertical crack extending and extending along the direction of the maximum principal stress appears at the bottom of the “V” shaped failure zone. When the strain concentration area of the coal around the borehole gradually develops into the butterfly shape, the coal above the borehole begins to move to the borehole space, the vertical crack expands rapidly along the direction of the maximum principal stress and deflects to the horizontal direction, and the acoustic emission signal increases sharply and reaches the energy peak. The vertical and horizontal cracks intersect to form an arch crack, and the coal wrapped by the arch crack is divided into independent blocks, and then the acoustic emission signal is significantly weakened.