Presplit Assessment by Signature Hole Blast Vibration with Accelerometer Measurement

摘要

The effectiveness of presplit in soft or fractured ground is hard to visualize or quantify. There have been many attempts by the blasting community to measure and quantify the effectiveness of presplit blasts. Various methods have been adapted by different researchers, and the results are debatable.The optimum presplit should provide the maximum filtering to the blast vibration amplitudes (e.g. PPA and PPV) and at the same time the presplit itself should generate the least amount of vibration amplitude to the highwall. This paper presents a new method to measure the effectiveness of presplit blasting by measuring blast vibrations using accelerometers. The accelerometers can measure much more accurately and for a wider range of frequencies and amplitudes than most geophones.Peak particle acceleration (PPA) and peak particle velocity (PPV) of the blast vibration are plotted against the charge weight scaled distance. The blast vibration difference between the blastholes fired before (without presplit filtering) and after the presplit (with the presplit filtering) are identified as the measure of the effectiveness of the presplit blasts and expressed on a percentage basis.The assessment shows a clear separation for unfiltered and filtered data by presplit in both Peak Particle Acceleration (PPA) and Peak Particle Velocity (PPV). With regression equations, PPA and PPV reductions can be estimated for a given scaled distance. Reductions in the order of 60% to 66% are currently being achieved at the test site for a scaled distance of 1.0m/kg0.5 (2.21 ft/lbs0.5). The presplit reduced PPV and PPA more effectively when the scaled distance is below 2.5 m/kg0.5 (5.52 ft/lbs0.5). PPV and PPA are directly related to energy, therefore the use of presplitting techniques reduces the amount of energy directed at the highwall and hence reduces the damage to the highwall.