In the context of its studies for the Ministry of Environment and for the French National Coal Board, INERIS (the French Institute for Environment and Industrial Risks, formerly CERCHAR) conducted a comprehensive critical study of the methods generally used to reduce Blasting vibration levels.
In general, it is recognized that the main parameter to control vibrations is the so-called “instantaneous charge”, or late charge. This should be reduced as much as possible to decrease vibration levels.
Because of this, the use of a new generation of blasting devices, such as non-electric detonators or electronic sequential timers since the 1970s, has been developed.
INERIS has collected data from approximately 900 blasting in 2 quarries and 3 open pit mines. This data includes “input” parameters such as the diameter of the well, the load, the space, the charge per well, the load per delay, the total triggered load, etc. . . They also include “output” measurements, such as the velocities of the peak vibration particles and the main frequencies. These data have been analyzed with the help of statistical tools of multiple variables.
The reduction of the delay load with the help of priming devices such as non-electric detonators or electronic sequential timers improves vibration levels, but only to a certain extent. After this point, the phenomena are much less controlled than in traditional pyrotechnic time and the disturbances seem more erratic. The total tripped load, the accuracy of the pyrotechnic delays and the timer setting also have a strong influence on the vibration levels.
Blasting tests were performed to evaluate new vibration control methods, such as the superposition of vibration signals. These methods seem to be accurate in many critical cases, but they would certainly be improved with better accuracy of the delays in firing. The development of electronic detonators seems to be the way of the future for better blasting control.