Drilling and blasting are some of the major aspects of Mining and to date bulk of rock excavation in the world is done by it. The largest consumer of civil explosives in the world is the Mining Industry.
The entire process of drilling and blasting is very basic, yet to be done with utmost precision and safety. The entrance of a drill hole is called color and the bottom end is called toe. In some areas, an orthodox approach is taken using a chisel and hammed to drill holes which is a tedious and slow process and the maximum depth achieved in this rarely exceeds 400mm.
The process of drilling involves penetrating the rock mass with a drill to create holes at a certain distance apart from each other using Jackhammer drill (mostly) and then in these holes mining explosives are placed and are connected with a wire to detonate, producing high-intensity shock waves and a large volume of gas trying to expand rapidly from smaller drill holes to pre-existing minor cracks and breaking the rock instantly
More often than not people prefer delayed blasting in areas where the rock mass is very compact and there not much breathing space for the rock to move part during the blast.
The most commonly used mining explosive is Ammonium Nitrate Fuel Oil (ANFO) which is cheap and easy to transport manufacture and store. The only drawback of Ammonium Nitrate Fuel Oil is its resistance to water which is poor, making it difficult to be used in monsoon.
The main objectives of a primary blasting are
1) Excavation of a planned volume of rock mass from within defined boundaries.
2) Achieving the desired rock fragment size. (Maximum & Minimum)
Certain accessories are also used along with ANFO in blasting like detonators, neo gel, etc which are safer and precise in terms of yield and fragment size.