The spectral control of ground vibration using electronic delay detonators

Abstract

Abstract The present work deals with the measurement and modelling of ground vibrations due to electronic delay blasts fired at three quarry sites and a motorway development site. The results show that, under favourable conditions, an electronic delay sequence may be designed to produce certain vibration frequencies in the ground at a given location. This is due to the accuracy of electronic delays as well as their flexibility for selecting any desired sequence. Thus it should be possible to control blast vibrations in resonant structures such as houses, bridges, grain silos and open pit walls. In this regard, the vibration amplitudes from electronic delay blasts exhibit characteristic frequency bands that are dependent upon the time delay intervals. Such spectral banding is usually not observed in pyrotechnic delay blasts because of their delay scatter. However, the present results also show that if the local geology is too variable, then it is possible that the vibration frequency is unable to be adequately controlled, irrespective of delay accuracy. Under these conditions, the vibration time waveform is unpredictable, and so, obviously, are peak motion measures such as the traditional vector peak particle velocity. In such situations, and with regard to vibration, electronic detonators will provide no clear advantage over pyrotechnic detonators. Electronic delays have the possibility of reducing ground vibrations at a particular monitoring location only provided the delay sequence is specially designed to do so. Even then, reducing vibrations at one particular location may not yield reduced vibration at other locations equidistant from the blast. In this regard the present trials also show that blast vibration depends on the location of the monitor with respect to the initiation point and the direction of initiation. Thus simply replacing a standard pyrotechnic delay sequence by the equivalent electronic delay sequence will certainly not guarantee an overall reduction in blast vibration.