This invention relates to a rock bed preliminary fracturing method and an apparatus for preliminary fracturing rock beds by drilling a hole in the rock bed then injecting water under high pressure into the drilled hole.
In recent years, the capacity of the ripper device has been improved with the development of large-sized bulldozers to such an extent that rock beds with an elastic wave propagating speed (Vp) of about 2,500 m/s can be excavated. However, on the surface of the earth, there are a great many hard rock beds with Vp of 2,000 to 4,000 m/s, and so a greater part of them has been excavated by means of blasting. In recent years, however, the restriction on the use of blasting process has become severe year by year from the viewpoint of safety and public hazard, and so it is presupposed that a mechanical fracturing process will be required in place of the blasting process.
However, in order to excavate such hard rock beds by means of the ripper device only, a very large-sized powerful bulldozer is required, but in view of technical, economical and operability aspects, it is not advantageous to carry out the excavation work by a mere combination of such large-sized bulldozer and ripper device. If, prior to ripping, pressurized water is injected into natural cracks of the rock bed to be excavated so as to expand such cracks thereby weakening and reducing the strength of the rock bed, and thereafter ripping thereof is made, then even rock beds with Vp of about 4,000 m/s can be excavated by means of a currently employed middle-sized ripper device, and therefore this excavation process is advantageous in both technical and economical aspects.