Finite Element Simulations of Blasting and Fragmentation with Precise Initiation

By using blasting caps with electronic delay units, it is possible to control the time of ignition between the boreholes of a mine. This has opened up new possibilities to optimize the blasting in order to achieve a better fragmentation which would significantly reduce the costs for the mining industry. The potential benefits of being able to control the ignition times has been described by Rossmanith [1], where stress wave interaction should according to theory and experience result in higher fragmentation, throw, swelling and digability. This theory has in this work been tested through Finite Element simulations using the LS-DYNA software. The rock material used is Westerly granite, which has been modeled with the RHT material model and it uses damage mechanics to describe the fracture of the rock. Also, a 2D-fragmentation evaluation routine has been proposed that makes it possible to study the level of fragmentation in section cuts of the Finite Element model. A 3D FE-model of two boreholes was used to evaluate the influence from ignition times, borehole distance and the amount of explosives. The results show that there indeed is a stress wave interaction effect and in this region there is an increase in fragmentation. However, the zone with increased fragmentation is considered to be small. The main effect on the fragmentation comes from the distance to the explosive charge and the amount of explosives.