Rock Blasting and Overbreak Control




1.1 INTRODUCTION Most raw materials, from which our modern society is built, are produced by the use of

explosives in mines throughout the world. The construction of highways, canals and buildings are aided by the use of explosives. The plentiful food, which is available in this country,

would not exist without explosives to produce the fertilizers and the metallic ores, which ultimately become tractors and other equipment.

The use of explosives in mining and construction applications dates back to 1627. From 1627 through 1865, the explosive used was black powder. Black powder was a different

type of explosive than the explosives used today. In 1865, Nobel invented nitroglycerin dynamite in Sweden. He invented gelatin dynamites in 1866. These new products were more

energetic than black powder and performed differently since confinement of the explosive was not necessary to produce good results, as was the case with black powder. From 1867 through the mid-1950's, dynamite was the workhorse of the explosive industry.

In the mid-1950's' a new product appeared which was called ANFO, ammonium nitrate and fuel oil. This explosive was more economical to use than dynamite. During the decades of the 1970's and the 1980's, ANFO has become the workhorse of the industry and approximately 80% of all explosives used in the United States was ammonium nitrate and fuel oil.

Other new explosive products appeared on the scene in the 1960's and 1970's. Explosives, which were called slurries or water gels, have replaced dynamite in many applications. In the late 1970's' a modification of the water gels called emulsions appeared on

the scene. The emulsions were simple to manufacture and could be used in similar applications as dynamites and water gels. Commercial explosives fall into three major generic categories, dynamites, blasting agents and slurries (commonly called water gels or emulsions).

Blasting problems generally result from poor blast design. poor execution in drilling and loading the pro~osed design and because the rock mass was imoroperly evaluated.

Blast design parameters such as burden, stemming, subdrilling, spacing and initiation timing must be carefully determined in order to have a blast function efficiently, safely and

within reasonable vibration and air blast levels.


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