Date of Award
Master of Science
This thesis is directed towards the comparison of active and passive bolts systems to reveal which system shows the most favorable behavior for improved performance, safety and cost. This was achieved through the incorporation of new technologies, field data, numerical modeling and established theories in ground control analysis. All in all, a better understanding of the quasi-static behavior of underground coal mine roofs has been attained. Over the summer of 2010, the Department of Mining and Mineral Resource Engineering at Southern Illinois University Carbondale, in conjunction with Andy Hyett of YieldPoint Inc., Peabody and the National Institute of Occupational Safety and Health (NIOSH), installed over one hundred and seventy instrumented extensometers, closure meters, shear-meters, passive rebar roof bolts, tension rebar roof bolts, and double lock rebar roof bolts at three coal mines. Two of the three coal mines were room-and-pillar mines and the other a longwall mine. Data was routinely collected over a nine-month period to analyze shearing, dilation, and axial bolt loading occurring within the rock mass, and entry closure occurring between the excavation hanging-wall and foot-wall. Based on bolt loadings, shear, axial behavior and statistical analysis, initial results indicate that active roof bolts do not show superior performance for the added cost. Active bolts seem to show no difference from passive bolts in the initial loading phase either, indicating that tension bleed-off is a concern soon after installation; however, this observation was not captured, as the data loggers were not intrinsically safe. Considering the modeling results, the trends in axial loading seem to be calibrated but the magnitudes are not. Computer modeling also shows the potential to accurately model in situ bolt performance; however, challenges remain in obtaining a good match between numerical modeling and field observations.
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