Experimental study on the failure characteristics and charge law of coal samples with large scale single pre-crack

In order to effectively extract the precursor information of containing macroscopic structural coal body in de- stabilizing failure,the authors have carried out the experimental research on the failure characteristics and charge sig- nal law of intact coal samples and coal samples with a prefabricated large different-dip crack under uniaxial compres- sion. The results show that with the decrease of pre-crack angle(the angle between the crack and the axial direction), the peak stress of coal samples decreases gradually,and the time reaching the peak stress de-creases,and the coal samples change from the tensile splitting failure to shear slip failure. At the same time,the new wing cracks are trans- formed from the wing cracks of the vertical pre-crack surface to the wing cracks of the parallel pre-crack surface. The pre-crack coal samples are more prone to rupture due to the existence of macroscopic cracks,and there are significant charge signals before the stress peak. Therefore,the precursory information of pre-crack coal samples is more easily captured than that of intact coal samples. With the pre-crack angle changing from 60° to 45° to 30°,the time of the first high-value charge signal in coal samples cracking process appears gradually advances,respectively 68. 5% σc and 65. 5% T,60. 5% σc and 47. 0% T,37. 5% σc and 30. 0% T(T for the whole destruction time of coal samples),and the amplitude of charge signal after the peak stress failure stage decreases gradually,as well as the mutation points in the charge accumulation curve increase and the first mutation point is advanced. The existence of pre-crack can affect the charge laws of coal samples by changing the deformation fracture process and the form of coal samples. Therefore, the charge signal related characteristics of pre-crack coal samples can be applied to detect the macroscopic geological structures and infer the occurrence of joints or faults of coal or rock mass reasonably. The study may provide new meth- ods and approaches for the prediction of coal and rock dynamic disasters.