Dynatec, Redpath pioneer latest shaft-sinking innovations

If there was a market for used mine shafts, Canada would surely be one of the world’s principal suppliers.

About 95% of the shafts would be rectangular with most of the remainder square. The term “square” for a shaft is something of a misnomer but that is how the industry knows them. There would only be a handful of circular shafts as most are recent sinkings and consequently still in use. As luck would have it, it is the circular type that would be in greatest demand. Despite the proliferation of shafts and the globally recognized skills of the Canadian miner, shaft sinking had remained a sleeper in this country until three years ago so far as technical innovation was concerned. In 1989 two independent mining contractors each started a new shaft-sinking project in the Sudbury Basin. These contractors were Dynatec Mining at the Craig shaft and J.S. Redpath at the T.L. shaft, both Falconbridge Ltd. properties.

At these locations, Canadian shaft-sinking practice took a leap forward and came at least abreast with the best that has been developed elsewhere in the world.

The reason for Canada’s atypical laggardness in this vital mining area is entrenched in history and not hard to identify. The cause is the benching cut; the term given to that layout of blastholes used to break the rock in the bottom of the shaft and so progressively deepen it.

In its essentials, half of the shaft bottom is drilled off and blasted. The broken rock from the blast is thrown up in a sloping pile against one end of the shaft and there is a depression carved out of the rock at the other. In the days when the only way to clear the rock was with a hand shovel the sloping rock pile was a Godsend. All the crew had to do was lay the sinking-bucket on the sloping pile and scoop the broken rock into it. There was no need to physically lift the rock on to a shovel to move it. The depression at the other end of the shaft made a natural collection point for water, and the pumps. This end of the shaft was also out of the way of most of the activity and a very important advantage in the confined space of the shaft bottom.

Though easy to describe on paper, shaft sinking in the days of hand shovelling was brutalizing work. Few men could stand the pace of the work today, let alone its rigor.

Soon after the Second World War came mechanization. First the Ridell mucker and then the Cryderman; very much later the cactus grab was adopted from South Africa. These machines did away with the hand shovel but oddly enough there was never a sustained effort to maximize the many advantages created by these new developments. Sinking continued to use the benching cut even though it had now been outmoded.

Elsewhere in the mining world and outside of North America, full face drilling and blasting had been practised for over a century (full face drilling and blasting simply meaning that the entire shaft bottom is drilled off and then blasted in one complete sequence).

The benching cut is outmoded because of its poor utilization of labor. The first task of the mechanical mucker is to level the steeply sloping pile of broken rock produced by each blast. A full face blast produces a flat pile of blasted rock as a matter of course, as well as creating a more efficient mining cycle and a more rapid rate of sinking.

It was not until Dynatec and Redpath came upon the scene that this unsatisfactory state of affairs was rectified.

Nearly 40 years elapsed from the introduction of mechanical muckers until the application of full face drilling and blasting. It is interesting to note the manner in which the two shaft contractors broke away from

an antiquated shaft-sinking method and, seemingly as compensation for so many lost years, added their own improvements. Without much doubt these improvements will be adopted by shaft-sinkers worldwide.

The details of Dynatec’s and Redpath’s equipment vary considerably but the basic practices are identical. It is these that have revolutionized Canadian shaft-sinking practice. They comprise the use of the burn cut in full face blasting and the application of electro-hydraulic drilling.

The burn cut is a cluster of parallel holes drilled very close together so that only a narrow rib of rock is left between them. When the holes are blasted, this remaining web is “burned out,” i.e., the explosive reduces the rock to dust. To break successfully, the holes must remain parallel throughout their entire length and this requires considerable skill and experience.

The Craig and T.L. shafts are probably the first projects anywhere to use the burn cut in a routine systematic manner. There is every possibility the cut may have been experimented with at shaft-sinking operations elsewhere from time to time. It may have been tried intensively in the Ashanti goldfield soon after the Second World War but it never came into use on a routine, day-to-day basis until 1989.

Electro-hydraulic drilling ensured the drilling of a cut that could be relied upon to break. Canadian contractors simultaneously solved the severe problems that had to be overcome in order to introduce this relatively new and powerful electrical drilling system into the confined and hostile environment of the shaft bottom.