Shaft sinking from 1970 to 2007: mechanical excavation
During the 1970 to 2007 time period, there were a number of changes to traditional shaft sinking systems, both in Canada and in other countries around the world. These include:
- the use of shaft jumbos for drilling;
- the use of electronic detonators for blasting;
- the use of hydraulic drills rather than pneumatic drills;
- the use of slurry explosives instead of nitroglycerine-based explosives;
- the drilling and blasting of long rounds utilizing drill jumbos suspended from the work stage;
- equipping the shaft simultaneously with excavation; and
- the development of mechanical shaft excavation systems.
It can be noted that during this period no improvements were made to the mucking, hoisting or concreting segments of the sinking system.
Shaft drilling jumbos were introduced in Canada in the 1970s and somewhat later in South Africa. Patrick Harrison & Co. introduced a six-boom “Acme” shaft jumbo at the Pipe Lake shaft in Thompson and a four-boom unit at the Lockerby ventilation shaft near Sudbury in 1972. The introduction of drill jumbos to Canadian shaft sinking was somewhat later than in the United States and Europe because of the popularity of the benching round in Canada. A full-face round was drilled with a shaft jumbo.
At about the same time as the pneumatic drill jumbos were introduced in Canada, the first hydraulically powered jumbo drills were being introduced in the tunnelling industry. However, it was not until the late 1980s that Canadian shaft sinkers started using hydraulically powered drills on their shaft jumbos.
In Canada, the “Long Round” shaft sinking system was developed in the late 1980s and early 1990s. This system utilizes a drill jumbo that is suspended from the sinking stage rather than sitting on the shaft bottom. The suspended drill jumbo drills a burn cut rather than a V-cut or cone cut that is normal in shaft sinking. Initially, the cut consisted of a series of closely spaced holes. Dynatec Mining of Richmond Hill, Ontario, pioneered the use of one or more large diameter holes (200 to 250 millimetres) for the cut instead of a series of small holes. A separate ITH drill is used to drill these large diameter holes.
During this time period, most Canadian shaft sinkers changed from electric detonators to non-electric systems. These new detonators are extremely resistant to accidental detonation by static electricity, stray electric currents, radio transmissions, flames friction or impact. Nonel shock tubing is one of non-electric detonating systems presently in use by shaft sinkers. The original Nonel system was first introduced in 1973.
Explosives used in shaft sinking have generally changed from the traditional nitroglycerine-based explosives to slurry or emulsion type explosives. Both slurries and emulsions are safer to use than nitroglycerine-based explosives. Melvin Cook, the founder of Ireco, invented slurry explosives in 1956, while emulsions were developed by Atlas Powder in the United States in the late 1960s.
Neither of these explosives were adopted immediately by shaft sinking companies, and it was only in the 1970s and 1980s that they became popular. Some shaft sinking companies still prefer to use the nitroglycerine-based explosives, despite the fact that they are more difficult to handle.
In the 1990s, a further improvement was made to shaft sinking efficiency — the bulk loading of explosives for shaft sinking. Both explosives manufacturers, Orica and Dyno Nobel, have assisted in the development of this method of loading explosives.
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