Blind drilling for shaft development

CIM Bulletin, Vol. 72, No. 804, 1979

JAMES H. COBBS, President, Cobbs Engineering, Inc., Tulsa, Oklahoma

Blind boring of shafts is becoming an increasingly important part of shaft sinking. Blind-bored shafts have reached diameters of 25 ft in Europe and 16-1/2 ft in the United States. Much of the technology developed for blind boring has evolved from the technology of drilling wells for oil and gas production.Blind boring offers economic advantage in a number of situations where conventional shaft sinking either is extremely difficult or very expensive by virtue of large-capacity aquifers which must be penetrated, unstable ground or where very rapid sinking is required. In sedimentary rocks, blind boring is cost competitive with conventional sinking, in diameters of about 12ft or less. Blind boring is not competitive with raise boring where conditions are favourable for raise boring. Blind boring does, however, offer greater flexibility than raise boring and can be performed in situations where raise boring is inefficient or impossible.Combination machinery has been developed to perform both blind boring and raise boring, so that the machine can be used effectively in situations where only the near-surface portions of the shaft are unfavourable for raise boring.Development work is being supported by the United States Bureau of Mines for blind boring equipment capable of boring shafts up to 30 feet in diameter.
Keywords: Underground mining, Shaft sinking, Drilling, Blind drilling, Boring, Raise boring, Drill pipe, Stabilizers, Bits, Cutters, Circulation systems, Shaft linings.