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A case study of bolt performance in a two-entry gateroad.
Proceedings of the 17th International Conference on Ground Control in Mining, August 4-6, 1998, Morgantown, West Virginia. Peng SS, Holland CT, eds., Morgantown, WV: West Virginia University, 1998 Aug; :249-256
This paper presents the results of a case study conducted in a two-entry gateroad in a coal mine where excessive roof deformation and bolt loading resulted in failure of many roof supports. The instruments consisted of 16 fully grouted, straingaged resin bolts, load cells on both full and partially grouted cable bolts, and vertical deflection multipoint extensometers. These instruments were installed on-cycle to measure loading on bolts in an existing support pattern and to determine if cable bolts could be used to improve roof stability. Results showed significant amounts of movement within the bolted zone. In some cases, these movements were enough to load the supports past their ultimate strength. Geology appeared to be a significant factor in localized roof degradation; that is, a very weak rock layer in the immediate roof overlain by a very strong rock layer contributed to the development of shear planes. Only one instrumented bolt had a maximum strain of less than 2,000 microstrain, which was the yield point of the steel. The average maximum strain on all bolts was 20,000 microstrain. However, electrical continuity to many gages was lost, and a pattern was noted that would indicate possible bolt failure. Wire mesh and concrete cans installed as secondary support performed very effectively.
Mining-industry; Coal-mining; Underground-mining; Mine-safety; Roof-failures
National Institute for Occupational Safety and Health, Spokane Research Laboratory, Spokane, WA 99207
Other Occupational Concerns
Proceedings of the 17th International Conference on Ground Control in Mining, August 4-6, 1998, Morgantown, West Virginia