Controlled fracture method and apparatus for breaking hard compact rock

Abstract

Hard compact materials, such as rock, concrete, et cetera, are broken by igniting an appropriately designed explosive or propellant charge placed within the hole or carried in a special charge-containing device with a short barrel which is inserted and sealed into a pre-drilled hole of particular geometry. One or more approximately cylindrical holes are drilled into the material to be broken by conventional drilling, such as used in the mining and construction industries. The holes have a relatively short depth to diameter ratio, being in the range of about 2:1 to 6:1, and preferably about 3:1 to 5:1. The holes are percussively drilled with microfractures in and around hole bottoms to provide fracture initiation sites at the hole bottoms so as to provide preferred fracture initiation roughly parallel to a free surface of material being excavated. The explosive or propellant charges may be any of several commercially available explosives or propellants, including standard military and commercial rifle powders and various recently developed liquid propellants. The propellant charges, whether solid or liquid, may be placed and ignited within a charge-containing device, which includes a short barrel inserted into the holes drilled into the material to be broken. The barrel of this device may be further sealed into the holes by a helical shim sealing method.