Long round concept benefits productivity, Dynatec Mining

During the sinking of the Craig shaft at Sudbury, Ont., Dynatec Mining says it developed the ability to drill and blast extremely long rounds. The concept was based on the use of a single large diameter drilled cut in lieu of a burn or shatter cut.

In November, 1990, Dynatec installed 5-metre slides and was successful blasting five metres per round in the 6.25-metre-

diameter shaft. The company says that to the best of its knowledge, this work has never been done in the world and it resulted in a huge productivity improvement on the project.

Because of the success of the long full-face rounds in the shaft, Dynatec decided in March, 1991, that a Jumbo would be built using the same concepts to drill and blast long horizontal rounds. The Jumbo construction was completed in October of that year and tested at the Gaspe Copper division of Noranda (TSE); 18 rounds were blasted using the 6-metre Jumbo that incorporated an in-hole hammer to drill the 250-millimetre diameter cut. The success of the Jumbo was immediate, Dynatec says, and extension steel was used to drill one 7.6-metre round and one 9.1-metre round to prove the potential of the long round concept.

The outstanding innovation is the ability to drill the large diameter cut hole simultaneously with drilling the blast holes, the company says. The use of the large diameter cut hole eliminates the necessity to drill a multi-hold burn cut that has limitations in the drilled length because of the necessity to drill the holes precisely parallel.

The company says the use of the large diameter cut hole reduces the skill level, ensures a more complete break in each round drilled and allows long rounds to be successfully excavated.

The development of the long round concept is primarily to improve the productivity of the drill and blast process, says the company. The problem with drilling and blasting is that it is not a continuous process. Each time a new cycle is started, there is a delay at the start and end of each of the cycles because of the changing of equipment and/or personnel. The longer the round, the more productive the process providing that each phase of the cycle maintains a minimum productivity that is equal to the original process.

Dynatec says it funded the development of the Long Round Jumbo on its own. The innovation is the use of an in-the-hole hammer to drill a large diameter cut, or relief hole, in lieu of drilling a multi-hole burn cut simultaneously with the blast hole drilling cycle.

Large diameter holes have been used as a relief hole in the past; however, the procedure was to use a machine that would be brought into a face where it would drill the relief hole often many times the length of the round to be blasted. Conventional drilling practices would be used to excavate the rounds until the end of the relief hole was reached.

The difference is that the use of a separate machine introduces a new element to the cycle, making the entire procedure less productive. The separate machine was extremely large and could not be incorporated with the blast hole drilling jumbo.

The impact of this innovation is in excess of a 20% improvement in productivity, Dynatec says.

The potential benefit to the Canadian mining industry is a reduction in cost for contracted services, the company says. A second more significant spinoff benefit to the mining industry will be the use of drill Jumbos for their development work utilizing the in-the-hole hammer to improve productivity through the use of longer rounds.

There is about $300 million worth of development carried out on an annual basis in the Canadian mining industry. Assuming that 50% of this development could benefit from the use of the long round technology and that the Long Round Jumbo results in a 20% improvement, then the immediate benefit would be in the order of $30 million per year in savings to the industry, Dynatec says.