A Study of Correlations between Rock Bolt Pull-Out Tests and Rock Mass Rating Scores in Underground Mining
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Rock bolt pullout testing is a common method of testing the strength of ground support in underground mining over time. Bolts that fail the pullout test fail either due to shear failure at the head of the bolt or by slipping in one piece out of structurally incompetent rock. There are many methods for quantifying rock mass strength; in this study, Bieniawski's Rock Mass Rating (RMR) system is used. This study focuses on the correlation between slipped rock bolt pullout tests with low RMR scores in underground mines. Underground mine sites participating in this study are located in Eastern Nevada, which is infamous for its low rock strength. Bolts used in this study are inflatable friction bolts, primarily Swellex bolts by Atlas Copco but with a few other manufacturers of inflatable friction bolts as well. When data was controlled for corrosive weakening of the bolt and normalized for bolt length, correlations between slipped pull-tests and low RMR scores were generally strong, positive, and statistically significant.