Measurement of air and ground vibrations produced by explosions situated on the Earth's surface

M Grobbelaar,T Molea,R Durrheim

doi:10.17159/2411-9717/978/2020

Abstract

SYNOPSIS Most equations used to predict the ground motion produced by explosions were developed using confined blasts that were detonated for breaking rock in mining or tunnelling. Ground motion is usually recorded by geophones or seismometers. The air blast produced by open-pit blasts and explosions on the surface can pose a significant risk, thus microphones and pressure gauges are often also used to monitor the effects of the explosion. The aim of this study is to determine whether the predictive equations developed for confined explosions can be used to predict the effects from explosions on the surface, with appropriate adjustments to the various coefficients. Three predictive equations developed for buried explosions were tested. The study shows that the US Bureau of Mines peak particle velocity (PPV) predictive equation is the most reliable. In addition, a predictive equation that uses the secondary atmospheric shock wave phenomenon also produced good results, and uses the scaled delay time parameter, which is easier to measure. These equations may be utilized for demolition sites, where old and potentially unstable explosives and obsolete equipment are destroyed on the surface, and for assisting in forensic seismology to determine the details of an unexpected and unknown explosion. Keywords: surface explosions, prediction, demolition, PPV, secondary shock wave.

Highlights

Military demolition sites are areas where old and potentially unstable explosives and obsolete equipment are destroyed
This study has identified a number of predictive equations that have produced acceptable results using data obtained from disposal of military ordnance that included the explosives and the casings/shells, the demolitions being conducted on the surface
The values for the atmospheric shock waves were easier to determine than those of the ground motion because the atmospheric shock waves are more prominent on the seismograms than those of the ground motion, due to the fact that very little of the energy is transmitted into the ground

Summary

Introduction

Military demolition sites are areas where old and potentially unstable explosives and obsolete equipment are destroyed. The ordnance is placed on the ground surface and detonated. The area should be located far from any human activity or dwellings, and is cleared prior to use. Some demolition sites have been encroached upon by human settlements. Modelling and monitoring of the ground vibrations and air blasts have become a priority to ensure that the blasts do not cause irritating disturbances to the local inhabitants or damage to structures, which may result in protests and legal challenges. Equations that could be utilized to predict the effects of the demolition activities on the surrounding population and structures would be useful in mitigating these risks

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