Experimental investigations on rock damage extent induced by three blast techniques

Abstract

In general, the size of excavation disturbance zone (EDZ) by rock blasting positively correlates with the explosive charge amount, hence a maximum allowable charge amount is usually adopted as the criterion of damage control. Such a charge-amount-limit, however, is not suitable to all cases. Three groups of blast tests have been carried out at the site of a nuclear power plant, being cut, bench and presplit blast, respectively. The EDZ of every single blast was determined by sonic wave measurements. It is observed that in common conditions, the EDZ of a cut blast is at least 2.5 times greater than that of presplit blast, while the difference between cut and bench blast is negligible. The results validate the rationality of a common practice: small-burden & big-spacing blasthole pattern in bench blast. To presplit blast, the optimal hole spacing for the formation of continuous fractures is 15 to 22 times of blasthole radius. In any case, slim-hole blast is more efficient in rock fracturing and damage.