Blast Vibration and Fragmentation Control at Heavily Jointed Limestone Mine

Abstract

The presence of structural inhomogeneity in a rock mass in the form of joints, fractures, bedding planes is a very common phenomenon. These discontinuities have a great influence on rock fragmentation as explosive energy is significantly affected by it. The extent of these discontinuities also has a great influence such as the thickness of the joint interfaces which varies from very tight joints to open ones. The amount of energy (or stress) generated by explosives, transmitted through the joints and energy can be passed over the interface resulting in poor fragmentation. The paper is based on the challenges faced during the study at Sangmania and Birhauli limestone mines to achieve the desired fragmentation as the rock formation of the area is dominated by joints and layered bedding. Experimental practices viz. drilling of holes, drill pattern designs, delay intervals and charging of explosives (with or without deck) have been performed to achieve desired fragmentation. Fifty blasts have been conducted at different quarries of Sagmania and Birhauli mines to determine the effect of both joint spacing and orientation on rock fragmentation. Two hundred thirty-six ground vibrations data have been recorded and compared for different prediction equations for better control on ground vibration. The in-hole velocities of detonation of explosives were monitored and optimal deck length and deck types were optimized to improve the fragmentation. The in-situ block size and blasted block size were determined to evaluate the efficiency of blasting.