Studies on the Vibration Level of Blasting Vibrations

This study aims to find a rational method to reduce the level of vibration in pre-blasting. The vibration level (VL, unit is dB) is used to express the intensity of the blasting vibration here in stead of the peak particle velocity. It is regarded that pre-blasting is made up of a series of single-shot-blastings (SSB) with time delay, namely, delay-blasting (DB) in this study. Experiments were carried out to obtain vibration waves from both SSB and DB. Attenuation of VL with distance from the source to the observation stations was estimated and compared with that of the peak acceleration for SSB waves. The attenuation factor of the VL was about one-sixth of that of the peak acceleration. This low attenuation of the VL is attributed to the fact that the duration time increases as the distance increases. As VL of the DB vibration depends on the time delay of SSB, it will be reduced by controlling the time delay. The dependency of VL on the time delay was examined by the artificial DB waves (ADB waves). First, ADB waves were made by superposing SSB waves with the same time delays as those of the experimentally obtained DB waves (EDB waves). The validity of the ADB wave was checked by comparing the wave form with that of the EDB wave. These two wave forms resembled closely each other. Second, (VL)_s were computed from ADB waves by parametrically changing the time delay from 20 to 200ms. The relationship between VL and the time delay was discussed and it was found that the longer the time delay the lower the VL. Finally, scattering of shooting time at each time delay was taken into consideration in ADB waves. There was little difference (VL)_s obtained from ADB waves with shooting scattering and those without the scattering.