Experimental Study On The Blasting Crack Growth Law In Coal

The blasting crack propagation law in coal, which is an important research of theblasting mechanism in coal, is a very complex research topic. It is difficult to researchthe blasting crack propagation law in coal for the complexity and particularity of theinternal structure characteristics and physical and mechanical properties in coal.Based on the relatively mature studies of the blasting crack propagationmechanism in rock, this paper discusses the blasting crack propagation mechanism incoal mass from the explosion stress wave, detonation gas and gas pressure; then itanalyzes the conditions, parameters and factors of the blasting crack propagation in coal.So it can provide a theoretical basis for the study. In addition, according to theclassification of coal, this paper selects a reasonable material and ratio to simulate thecoal, prefabricates the initial crack in coal, simulates the blasting test of the coalsamples with the initial crack and studies the explosion stress wave propagation law,blasting crack propagation velocity and blasting effects in coal.The results show that: the explosion stress wave in coal decays as power function,the attenuation index decreases with increasing coal strength and distance, and it isabout2.9; Initial crack can guide the blasting crack propagation in coal, the peak strainon the crack propagation direction is greater than that on others; The blasting crackpropagation velocity in coal is less than that in rock, and it decreases with thedecreasing coal strength; For the same type of coal, the crack propagation velocitywithin the coal is greater than the surface of the coal, it decays rapidly during the initialcrack propagation, then it expanses uniformly for a moment, finally it reduces to zeroand the expansion stops, and the time for uniform expansion decreases with the coalimpedance; When the initial cracks in the coal is more, it is easy to crack, but the crackpropagation velocity and the decay rate in the early expansion is less than that of theless initial crack in coal, the crack propagation is not sufficient. The gas pressure helpsto expand the blasting crack propagation in coal, and the number and scope of cracksexpand as the gas pressure increases.