ABSTRACT
In mining and construction, earth excavation is an everyday part of the job. The most economical method for earth excavation is, of course, mechanical attack. In open-pit mining production blast holes are generally vertical, although in recent years some mines have used angled drill holes to great advantage. Metallurgically much work has to be done on rotary percussion drilling but it may well be the next significant advance in the art of drilling. A prime factor in percussion drilling is the type of mountings, of which there is a variety. Once rolling cutters were introduced, subsequent improvements in tools made rotary drilling adaptable to harder formations. Supplemental energy is applied in oil-well rotary drilling by impingement of the circulation fluid (usually drilling mud) on the bottom through jets in the bit. Line drilling consists of a single row of closely spaced, unloaded, small diameter holes drilled along the neat excavation line.
