2008G Volume 2 - Signature Hole Blast Vibration Control - Twenty Years Hence and Beyond

In the early 1980s, a method for controlling blast vibrations other than by modifying the Scaled Distance came into use. Research studies had indicated that blast vibration could be simulated by detonating a signature hole with the vibration monitored at critical locations, and then using a computer to superpose the waveforms with varying delays. By choosing delay times that create destructive interference at frequencies that are favored by the local geology, the “ringing” vibration that excites structural elements in houses and annoys neighbors could be reduced. At that time, pyrotechnic detonator firing times were less accurate than they are today, and electronic detonators were only in the early stages of development. Since accurate delay times are crucial to effective vibration control, scatter in the firing times limited the method severely. As time has gone on, both the tools and the techniques have improved. Electronic detonators now have scatter less than a millisecond. Computers, of course have increased in speed phenomenally, and software keeps pace. In light of all these changes, many researchers and practitioners have extended and modified the original work, finding both limitations and new potential. This paper will review the history of the method, the assumptions made, the impact of increased detonator accuracy, and successes and failures of the method. Implications for future control methods, for both surface and underground blasting, will be discussed, as well as using vibrations to assess the effectiveness of the explosives. Copyright © 2008 International Society of Explosives Engineers 2008G Volume 2 Signature Hole Blast Vibration Control Twenty Years Hence and Beyond 1 of 12 Introduction For as long as the ISEE (and its predecessor SEE) has been around, blast-generated vibration and airblast have captured a lot of attention. Long before the Society’s inception, research and development addressed the fundamental problem of controlling the wasted explosive energy that goes into vibration. Early efforts focused on determining what “level” of vibration would cause annoyance or damage, and what methods could be used to assure a blaster that he or she could work effectively without worrying about neighbor problems. Simple solutions to engineering problems are generally preferred; to reach a simple solution, it helps to first simplify the problem. In the US, research by the Bureau of Mines from the 1940s and later developed simple methods to classify and address the problem of damaging vibrations. As we all know, peak particle velocity (PPV) was chosen as a descriptor that could be related to damage occurrences. Research elsewhere came to similar conclusions, though the details varied. Regulations followed from recommendations, which in turn followed from the research. The research showed that by knowing distance D and charge weight per delay W, (Scaled Distance W D / = ), one could reasonably predict the resultant vibration through a power law relation: