Mechanical response of split-set rock bolts in squeezing ground.
Williams-T; Bayer-D; Brady-T; Pakalnis-R; Varley-F
Proceedings of the 24th International Conference on Ground Control in Mining, August 2-4, 2005, Morgantown, West Virginia. Peng SS, Mark C, Tadolini SC, Finfinger GL, Khair AW, Heasley KA, eds., Morgantown, WV: West Virginia University, 2005 Aug; :366-371
Researchers from the National Institute for Occupational Safety and Health's Spokane Research Laboratory installed Split-Set rock bolts instrumented with strain gauges to document the mechanical load response of the bolts in weak ground. Short-term monitoring of the bolts immediately after installation showed that some of the gauges went into tension. It was felt that the force exerted on the bolts to drive them into the hole should have caused the gauges to show compression. The tension probably resulted from the holes having crooked sections. Long-term monitoring over the course of a year also showed that the bolts were bending at some locations and that loads as high as 98 kN (22,000 lb) were recorded along sections of the bolts. Load cells were placed on the head end of the bolts to determine head loads. Head loads up to 14.7 kN (3,300 lb) were generated during bolt installation. In addition, closure readings were taken across the drift to determine the convergence rate responsible for bolt loading. A Rock Mass Rating (RMR) was calculated at the site to compare with bolt response. The bolts were installed as part of the rebolting process in an area being repaired because the near-vertical beds in the walls were buckling and causing the wall to fail. The instrumented Split-Set rock bolts will provide data that will lead to greater understanding of the behavior of the rock/bolt support mechanism. It may also be possible to explain the overall performance of the bolts in situ in terms of their design effectiveness. This work showed that load at the head of a Split-Set rock bolt was less than load along the interior of the bolt.
Ground-control; Injuries; Coal-mining; Safety-research; Hazards; Models; Computer-software; Mining-industry; Longwall-mining; Geology; Underground-mining; Geophysics
NIOSH Pittsburgh Research Laboratory, P.O. Box 18070, Pittsburgh, PA 15236
Peng-SS; Mark-C; Tadolini-SC; Finfinger-GL; Khair-AW; Heasley-KA
Proceedings of the 24th International Conference on Ground Control in Mining, August 2-4, 2005, Morgantown, West Virginia