Statistical models for ground vibration and airblast

It is becoming increasingly important to be able to predict and reduce ground vibration and airblast so that mine operations may achieve their environmental requirements. The observed vibration and airblast at any monitoring location is influenced by variables such as the weight and type of explosive used per delay, the delay time sequence, scatter in that sequence, the spatial pattern of blastholes and properties of the transmitting medium. The present work shows how the separate influence of these variables may be analysed using a Monte Carlo model that has a predictive power superior to that of the traditional charge weight scaling laws. Charge weight scaling laws have sometimes been observed to give acceptable predictions at a fixed monitoring location for the consistent use of a particular blast design. However, unlike the Monte Carlo model, such laws cannot be used to predict the likely changes in vibration due to any planned changes in blast design. Monte Carlo predicted contours of airblast and vibration show that the blasthole locations and the direction of initiation have a considerable effect at any monitoring location. This is due to influences such as the finite travel time of the disturbance as well as the screening effect. The travel time delay between blastholes is more significant for airblast since the velocity (334 m/s) of sound in air is typically 10 times lower than the speed of vibrational waves through the ground. It is also well known that previously fired blastholes may provide a screen for both airblast and vibration produced by a current hole as it initiates. In the case of airblast, screening may occur due to the airborne particulate matter produced by previous holes; in the case of vibration, screening may occur due to ground fractured by these previous holes.