Evaluating pre-split performance through direct measurements of near field acceleration, particle velocity and gas pressure

Abstract

Pre-split techniques are routinely used to minimise rock mass damage from production blasting. Design parameters rely on site-specific guidelines and in order to improve designs, it is important to be able to measure its performance. One criterion is related to the pre-split ability to adequately filter blast-induced stresses and explosion gases. This paper presents the results of a monitoring program implemented to evaluate the performance of pre-split practices. Triaxial accelerometers and pressure sensors were installed behind pre-split lines and a site-specific criterion was established to determine whether or not filtering effects were occurring. The recorded maximum peak particle velocity (PPV) vector sum behind pre-splits in all blasts monitored was below the threshold of damage of intact rock and rock mass discontinuities. With regards to the recorded gas pressure, measurements from production blasts showed fluctuations of low pressure levels, indicating that pre-split parameters were effectively filtering-induced stresses and gases.