Bursting liability and energy dissipation laws of prefabricated borehole coal samples

Uniaxial loading test of pre-drilled hole samples was carried out based on the measurement methods of bursting liability of coal to study the mechanical properties and bursting liability of samples.Combined the fractal dimension and the newly added surface area of broken particles,the energy dissipation characteristics of coal samples during different drilling arrangements were analyzed.The results show that the drilling makes the failure form of the sample change from shear splitting to a failure form of gestation and fusion of cracks on both sides of the hole,and form through cracks between the rock bridges,accompanied by collapse.As the number of drill holes increases,the drilled samples show a gradual increase in pre-peak plastic damage,and gradual decreases both in the peak strength and the accumulated elastic energy,the post peak damage reflects the trend of prolonged time consuming and increased energy consumption.The uniaxial compressive strength,the bursting energy index and elastic strain energy index are both significantly reduced,the duration of dynamic fracture is significantly increased,and the bursting liability is reduced.The fractured particle fractal dimension is negatively correlated to the newly added surface area,the lower the degree of fragmentation of the sample,the higher the fractal dimension,the smaller the newly added surface area.The input,dissipation of energy before the stress peak of the sample have no obvious relationship with the newly added surface area.The law of energy release and dissipation after the peak of the samples are consistent with the distribution law of the newly added surface area of the crushed particles.The larger of the newly added surface area,the more energy consumption after the peak.Affected by loading rate and drilling layout,the energy difference after the peak and the new surface area change show a U shaped change trend.Drilling slows the rate of post peak energy release and energy dissipation of the sample,and the reduction amplitudes of the two are relatively similar.The single hole sample reduces by about 17.0%,the double hole sample reduces by about 68.3%,and the three hole sample reduces by about 70.8%.The test results show that borehole pressure relief reduces the accumulated strain energy before the peak,and reduces the energy release per unit time after the peak,making the sample less prone to dynamic damage.