Laser verifies deviation just 0.01% in 450-ft-deep hole, 8.5

The hole broke through on target in the middle of an 8-ft-wide drift. Subsequent verification by laser beam indicated a total deviation of just 0.75 inches or 0.01%.

The 8.5-inch pilot hole, to be reamed later to 5-ft diameter, was drilled from the 300 to the 750 level using a REDBORE 40 raise drill manufactured in Canada by Redpath Manufacturing. Under contract to Inco to drill a straight hole, Redpath used the opportunity to conduct a research and development project to demonstrate a directional drilling system (DDS) in a mining environment.

Developed by Bergbau-Forschung and Schwing Hydraulik Electronik of West Germany, the DDS is designed to provide automatic active directional control for the drilling of pilot holes. In Europe, the use of the DDS for both up and down hole drilling has resulted in better than 0.01% accuracy most of the time.

The key to the system is a directional drilling rod mounted immediately behind the drilling bit and designed to be an integral part of the drilling rod column. It is used for the pilot hole drilling only and is removed before reaming begins.

The DDS is 79 inches long and provides directional control by means of hydraulically actuated steering runners applied to the borehole walls. The verticality of the rod is controlled by a high accuracy inclinometer enclosed in the unit capable of detecting vertical deviation of one angular minute (one-sixtieth of a degree).

Monitoring equipment installed at the collar provides the operator with a continuous read-out of the bit orientation, thereby confirming that the system is functioning properly at all times.

Redpath says that, once fully commercialized, this “technological breakthrough” is expected to have a significant impact on specialty applications in the mining and heavy construction industries for very long holes and holes where accuracy is important such as borehole hoisting systems, penstocks, deep freeze holes and fill holes.

Redpath has a fleet of 13 raise drills operating coast to coast in its efforts to introduce automatic directional drilling to North America. The directional drilling rod was recently on display at the Canadian Institute of Mining and Metallurgy’s annual convention and trade show at Quebec City.

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