Evaluation of parameters effecting blast induced vibrations

The following research focuses on the effect of measuring blast induced vibrations and the effect of the monitoring equipment and procedure on the outcomes. Mining and quarrying operations today are faced with ever increasing restrictions on their operations especially in the environmental field. Development applications for new operations have to contend with environmental issues such as dust, air pollutants, blast induced vibration and noise levels that at times restrict production outputs. Vibration monitoring has become an integral part of the mine/quarry operations and it is essential that the operators have confidence in the equipment that is used to measure these environmentally sensitive parameters. These issues were addressed in this thesis in both a laboratory investigation and a more practically oriented set of field trials. A standard technique used for measuring blast induced vibration levels was investigated and the error associated with the procedure was detailed. This standard technique was then compared to other commonly used mounting techniques. Some of these techniques have been accepted by the industry for many years basically because they are easy to carry out and do not require much time to set up. The errors encountered during this comparative trial were attributed to the poor bonding of the soil to the mounting device. This study was focused on the practicality aspect of vibration monitoring. The procedure recommended was found to have small random errors which were attributed to the complex nature of the vibration wave travelling through the ground. The laboratory investigation highlighted areas where care should be taken when bonding the mounting block to a soil type environment. Field trials were conducted in both surface and underground mining operations and a large range of vibration levels were used as the vibration sources for these trials. A n understanding of the vibration waveform and the importance of examining this waveform was discussed. The on screen display of all vibration monitoring equipment can give a misleading result as only the peak levels are displayed on the screen. What caused this peak level was examined. A special purpose laboratory vibration rig was designed and constructed to test some of the soil properties and their effect on the vibration wave transmission through the soil. The standard monitoring technique was used in the laboratory study to test properties such as moisture content of the soil, compaction of the soil in close proximity to the mounting block, type and size distribution of the soil. All of these soil properties had an effect on the vibration transmission through the soil and this effect was quantified. The fields trial phase of this study was mainly carried out at a local open cut coal mine. This coal mine site proved ideal as the frequency of the blasting operation allowed for a large number of trials to be carried out in a small period of time. Also the operations had variable explosive charge weights per delay and the distance from the blast to the monitoring location was regularly varied. In the field trial phase of this study the variability of the standard technique was investigated and the error level that could be expected was quantified. A comparison between typical mounting techniques and the standard technique quantified errors that could occur with these other methods. The density of the mounting block was also investigated with no significant change being measured for a large range of mount densities used. The investigation led to many conclusions and recommendations as follows: 1. The coupling or bonding of the soil to the monitoring equipment was found to be the most important factor. 2. A vibration monitoring procedure and equipment was recommended for soil monitoring applications. 3. The variation in the recommended procedure was measured and measurements within 1 0 % of each other were shown to be similar because of the nature of the vibration wave travelling through the ground. 4. Variations in industry accepted mounting procedures were shown to be quite significant with the recommended procedure having a sound scientific background. 5. Modern day electronics have made important advances in the equipment used to monitor blast induced vibrations and careful selection is recommended. 6. Analysis of the blast induced vibration waveform was shown to be critical as erroneous results can occur if instrument read outs are only used. 7. Vibration monitoring and subsequent modelling and prediction can play a useful role in establishing greenfield site vibration data