In high explosives, a shock pressure spike at the reaction front travels through the explosive before the gas energy is released. There are, therefore, two distinct separate pressures resulting from a high explosive and only one from a low explosive. The shock pressure is a transient pressure that travels at the explosives rate of detonation. The gas pressure follows thereafter.
Archived The shock energy is commonly believed to result from the detonation pressure of the explosion. The detonation pressure is a function of the explosive density times the explosion detonation velocity squared and is a form of kinetic energy.
Determination of the detonation pressure is very complex. There are a number of different computer codes written to approximate this pressure. LJnfortunately, the computer codes come up with widely varying answers. Until recently, no method existed to measure the detonation pressure.
The detonation pressure or shock energy can be considered similar to kinetic energy and is maximum in the direction of travel, which would mean that the detonation pressure would be maximum in the explosive cartridge at the end opposite that where initiation occurred.
It is generally believed that the detonation pressure on the sides of the cartridge are virtually zero, since the detonation wave does not extend to the edges of the cartridge. To get maximum detonation pressure effects from an explosive, it is necessary to place the explosives on the material to be broken and initiate it from the end opposite that in contact with the material.
Laying the cartridge over on its side and firing in a manner where detonation is parallel to the surface of the material to be broken reduces the effects of the detonation pressure. Instead, the material is subjected to the pressure caused by the radial expansion of the gases after the detonation wave has passed.
Detonation pressure can be effectively used in blasting when shooting with external charges or charges which are not in boreholes. This application can be seen in mud capping or plaster shooting of boulders or in the placement of external charges on structural members during demolition.
Reference
Rock Blasting and Control Overbreak, National Highway Institute, US. Department of Transportation
