Date of Award
Master of Science
Despite progress in research related to ground control, roof falls remain a major problem leading to injuries and fatalities in underground coal mines. Around 68 million rock bolts are installed annually in coal mines in the USA (Tadolini and Mazzoni, 2006), of which 68% of primary supports in coal mines are fully grouted resin rebar bolts. A fully grouted rock bolt is one that is fixed inside the drill hole by means grout, and is fully encapsulated throughout the length of the bolt. Production in underground coal mines is achieved by the combined processes of excavation and ground support, carried out in a cycle. Primary support is that which is installed on cycle during production. Secondary support is that which is installed in addition to primary support, i.e., out of the cycle, and typically in intersections where the effective span is much larger making extra support both appropriate and necessary. Although safe and effective, there is still considerable opportunity to improve the performance of fully grouted resin rebar. The objective of this thesis is to measure and study key installation parameters of fully grouted resin bolts to optimize their performance. This will be accomplished by conducting a series of lab tests, developing a new small-scale test method, performing in situ tests, and numerical modeling. With a research collaboration between the Department of Mining and Mineral Resources Engineering at Southern Illinois University Carbondale (SIUC) and Orica Americas funded by the Illinois Coal Research Institute (ICCI), almost two hundred pull tests (ASTM F432) were conducted mainly at the Orica North American Innovation and Technology Center in Bowerston OH, but also at two underground coal mines in the Illinois Basin. Laboratory testing consisted of rock bolt pull tests in a basically homogenous and isotropic material (concrete block) and hardness tests by modifying a drill press by varying key installation parameters. In situ testing consisted of rock bolt pull tests to at two different mines (Mines A and B). These were analyzed and optimized to better understand the performance of grouted rock bolts. Pull tests were conducted at SIUC’s Coal Research Center high-bay laboratory in Carterville, IL to investigate the effect of glove fingering when installing #5 and #6 rebar. Finally, a series of tests were performed to study the behavior of axial load shedding (creep) with time in grouted, tensioned rock bolts using U-cells (Mitri, 2012) and conventional load cells followed by a basic numerical modelling on the pull test. It was found that spin time and rotational speed play significant role to obtain a more effective fully grouted rebar system. An eccentric action was added to the wrench used for installing the bolts had no significant impact on the pull out load at in situ conditions but showed increase in the pull out load, when the installation procedure was altered. Resin hardness can be used as parameter to predict the pull out load of fully grouted rock bolt system and a significant creep was observed in the fully grouted tensioned rock bolts.
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