Abstract
SUMMARY A new type of roof bolt dynamometer has been developed to monitor changes in bolt tension with precision of +/-25 N. These dynamometers were installed in an Eastern Kentucky drift coal mine. At the monitoring site the immediate roof of Coalburg seam is composed of shale of varying thickness up to 1 m; thus the 1.2 m bolts were anchored in all cases in the overlying sandstone. The selected site was located in an intake airway about 600 m from a portal. It had a potential for roof problems due to sharp variations in air humidity, which is known to contribute to roof deterioration. Observation holes drilled in the mine roof were used for borescope inspection with miniature TV camera to localize and measure separation planes in situ. During the one year monitoring period the roof deteriorated considerably. Field data for this period illustrate changes in shaly roof. Analysis of the results is used as a base for the identification of the roof failure phenomena.
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