Abstract
The fundamental problem in rock working is the breakage of fragments out of the face of a solid wall of rock. Mechanically this can be done only by forcing a tool into the rock surface, after the manner of an ‘indenter’ such as is commonly used for testing surface hardness. Since the process breaks rather than cuts solid rock into small fragments of assorted sizes it can be regarded as essentially one of crushing. As in crushing processes generally, energy/volume relationships are therefore of interest. ‘Specific energy’, defined as the energy required to excavate unit volume of rock, is a useful parameter in this context and may also be taken as an index of the mechanical efficiency of a rock-working process. In drilling data from a number of sources its minimum value appears to be very roughly correlated with the crushing strength of the medium drilled in, for rotary, percussive-rotary and roller-bit drilling. The implications of this are discussed.
Published Version
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