The true triaxial test of strain field and acoustic emission response of bearing failure of coal with prefabricated borehole
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 gradu-ally 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 concen-tration 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 direc-tion,and the acoustic emission signal increases sharply and reaches the energy peak.The verti-cal 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.
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