Model for energy-based evaluation of blast waves to assess safety of structures

Abstract

Demand for safe and undamaged periphery rock walls in mining and civil construction projects has encouraged blasting engineers to study the details of controlled blasting parameters. Various researchers have proposed recommendations for optimizing blast design and safe magnitude of vibration. However, these recommendations require improvements. The magnitude of a vibration can be characterized by reflection of strata condition, explosive properties and the blast pattern implemented. It is thus proposed that, in order to develop a safe blast pattern to achieve undamaged periphery rock wall, the characteristics of wave signatures and the energy transferred to the rock medium should be analysed. This paper analyses the characteristics of vibration waves for various charge diameters (25 to 269 mm). To study the characteristics of wave signatures, wave analysis software was used to analyse various parameters of wave signatures, e.g. duration of vibration, magnitude of peak, number of peaks, acceleration/deceleration of peak, energy transmitted to the in situ rock in terms of total energy and energy of peak hold. It was observed that for small-diameter charged holes, the duration of vibration was short and the magnitude of vibration attenuated at a faster rate. Use of a long delay between rows and a jumped long delay between buffer and periphery row further dampened the magnification of vibration amplitude and duration of vibration for each delay. The magnitude of transmitted energy (total and peak hold) was less for small-diameter charged holes and varied with linear charge concentration and volume of rock per hole to be blasted. For large-diameter blast holes, vibration signatures had more peaks and of longer duration, indicating a high magnitude of strain and poor strain rate. Considering the quantum of energy transmitted by various charge diameters, this paper demonstrates that large-diameter charged holes produce a high magnitude of strain with poor strain rate and should be avoided for controlled undamaged perimeter blasting. For pre-split blasting with even a small quantity of explosive, the magnitude of transmitted energy was greater than for smooth blasting and should thus be avoided where smooth blasting can be implemented.