Fragmentation controlled blasting

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(1) The dynamic fracture process in Hopkinson's test was analyzed using proposed finite element method to verify the strain-rate dependency of dynamic tensile strength. It is clarified that the strain-rate dependency is due to the stress concentration and redistribution mechanism in the rock. The rock inhomogenety also contributed to the strain-rate dependency.(2)The fracture process in one free-face rock was analyzed to investigate the fracture pattern and its mechanism. It was cleared that the fracture process as well as the fracture pattern were affected by the applied pressure-rate. The transition between quasi-static and dynamic fracture process can be estimated by the non-dimensional time defined by the propagation velocity, the burden and rise time of the applied pressure.(3)A numerical simulation method, coupled the finite element arid the finite difference calculation, to analyze the multiple fracture propagation due to stress waves and the detonation gas is developed. It is c … More onfirmed that the detonation gas considerably affects the generation and propagation of the fractures and that he numerical gas-propagation velocity along the fractures approximately agrees with that obtained by the laboratory experiments. It is concluded that the gas velocity along the fracture in bench blasting is lower than the air sound velocity except for the vicinity of the blast hole.(4)A method to predict the fragment size distribution in bench blasting using numerical and image analyses was proposed. In this method, the fracture process in bench blasting was analyzed using proposed FEM and fragment size distribution was evaluated by the image analysis of FEM result.(5)Rock fragmentation in bench blasting was examined using proposed method and the influence of blast condition on fragmentation was clarified. It is recognized that the widely spaced blast pattern is effective to reduce the bolder in fragments. Furthermore, it is pointed out that the optimal fragmentation in the field with respect to delay time depends strongly on the gas flow through the fractures caused by the stress wave. Less