On borehole pressure and spacing in cautious blasting with an extension to water-filled holes

Abstract The evaluation of borehole spacing in presplitting and smooth blasting is closely connected to the evaluation of borehole pressure. Pressures required for splitting the rock, using the classical simple theory of pressurized uncracked holes in an infinite medium, are calculated for the case of granite cutting with detonating cord, and compared with a variety of estimations available. A survey of these approximations evidences a fairly large spread in borehole pressure values. Of them, the classical Calder pressure estimation leads to spacings, from the simple theory, quite consistent with reality. The presence of water as coupling medium between the explosive and the borehole wall affects both the borehole pressure and the spacing required. Blasts in granite with detonating cord of several explosive loads per meter have been conducted to analyze such effect. From the maximum allowable spacings, the borehole pressures are estimated. A correction factor for the calculation of borehole pressure in water-filled holes from the fully decoupled pressure is from that derived.