Mining - Analysis of Explosive Action in Breaking Rock

A method of analyzing blasting action indicates that major cost savings are possible by revising practice and bringing the classical blasting formulas up to date; difficult problems such as taconite and throw-breakup can be attacked by engineering Denonation pressure — the peak pressure developed by the explosive reaction; "shatter blasting." Average detonation pressure — the average pressure over the time the reaction continues; "heave blasting." Radial presswe — the stress in a radially expanding sphere about the detonation. Corresponds to the diminishing peak pressure. Lateral stress - the stress in a circumferential direction, induced by outward movement of the rock away from the detonation. Limiting stress or Slim— the rock property at which failure will occur in the case at hand; may be tensile or compressive strength, or combinations. Recent developments in explosives technology, following the advent of nuclear explosions, have led to a rather complete understanding of their action. A survey was made for the purpose of uncovering any knowledge which might be applicable in the mining and quarrying industries, the principal users of explosives. Although no revolutionary techniques have become apparent, much basic data pertaining to blasting — fortunately not classified — have been developed by recent research, from which a good general understanding of the process can be derived. It is hoped this explanation of the scientific principles governing explosive action, together with a proposed analysis of blasting practice, will further the development of mining engineering. NATURE OF THE REACTION: The phenomenon of explosion, termed detonation, is in reality a rather complex chemical reaction, and as such is completely explainable by physical and chemical laws. Detonation is characterized by high temperature and pressure, extreme rapidity — often being complete within one microsecond — and most importantly by formation of a shock pulse which accompanies the reaction zone. As with any chemical reaction, there is a critical value of temperature and pressure below which detonation can not occur; this is termed the "critical point". Whereas an explosive substance will decompose slowly at ordinary temperature, with the formation of gases which readily dissipate; at elevated temperature the reaction is considerably speeded. If pressure is suddenly applied at some point in an explosive medium, adiabatic compression results, and the temperature is locally raised. When the temperature becomes high enough the decomposition will be so rapid that the gaseous products do not have time to dissipate, but contribute to a further build-up of pressure. This, in turn, furthers adiabatic temperature rise over a widening area, and with any heat generated by an exothermic reaction, causes a rapid increase in temperature. Both temperature and pressure are spontaneously built up in this manner until the critical point is reached, resulting in detonation. The values of pressure and temperature necessary to create detonation are established by the unusual nature of the process. If temperature alone is raised above the critical point, without sufficient increase in pressure, deflagration or "low-order detonation" occurs. In the true, or "high-order detonation", the shock pulse resulting from the violent decomposition becomes an integral part of the reaction, and itself aids in increasing the detonation