Importance

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Abstract

Rock and other hard materials, such as concrete, are broken by a controlled-fracturing process referred to as penetrating-cone fracture. The fracturing process is accomplished by pressurizing the bottom of a drill hole in such a way as to initiate and propagate a controlled fracture from the sharp hole-bottom corner while not crushing the surrounding rock. A cartridge containing a propellant charge is inserted at the bottom of a short hole drilled in the rock. The cartridge is stemmed by a massive bar. A firing pin in the stemming bar strikes a primer which then ignites the propellant in the cartridge. The cartridge incorporates a relief volume designed to control propellant burning rates and pressures and thus the pressure at the hole bottom. The cartridge is designed with a tapered wall, which is thicker nearer the stemming bar, and with a large radius of the inside surface of the cartridge base, which reduce the possibility for premature cartridge rupture and loss of propellant generated gases. A sealing mechanism on the stemming bar may also be used to form a seal near the hole bottom. The stemming bar is preferably connected to a boom mounted on a carrier. A preferred embodiment incorporates an indexing mechanism to allow both a drill and a stemming bar to be used on the same boom for drilling and subsequent charge insertion and firing operations. The major features of the method and apparatus are the relatively low energy of the flyrock and the relatively small amount of propellant required to break the rock.

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First Claim