The implementation and quantification of the Vallejos and McKinnon re-entry methodology

The occurrence of seismicity in high stress hard rock mines poses a challenge to geotechnical engineers and mine management around the world. Only a few practical options are available when the mitigation of seismic risk is considered. One of the most widely used options is the implementation of a reentry protocol. These protocols are useful at limiting personnel exposure to elevated seismic hazard associated with the occurrence of a firing. There are several methodologies available for determining an appropriate reentry time. The success rate of these methods varies between sites. Recent work by Vallejos and McKinnon (2010) suggest a new approach to the reentry problem. They provide methodology that could be implemented on any mine site with a seismic system. The method evaluates the current response in terms of the statistical properties of the rock mass based on historic responses. Discussions on the practical implementation of the method on a site-wide basis were limited, and did not provide an indication of what could quantitatively be expected from the method. The Vallejos and McKinnon method could be automated and practically implemented on most mine sites with a comprehensive seismic data record. It was shown the methodology, in some cases, may be an improvement on the widely used ‘blanket’ rule implemented on many mine sites.