26th U.S. Symposium on Rock Mechanics, Rapid City, South Dakota, 26–28 June 1985
Authors: H. N. Maleki and M. P. Hardy (AAI), and C. J. H. Brest van Kempen (Brest van Kempen & Associates, Inc.)
Performance characteristics of an instrumented bolt utilizing the vibrating wire gages were evaluated through 140 field and laboratory tests. Evaluations consisted of instrumented bolt stability, repeatability and accuracy as affected by field installation factors, i.e., tension, torsion and bending moments. Bolt bending moments are present in field installations due to non-squareness of the mine roof and the bolt hole. The testing revealed several problems with the instrumented bolt, requiring redesign of the instrumented bolt assembly. Improvements in the instrumented bolt design included using a stronger bolt unit coupled to a standard 5/8-in. (15.8-mm) shank and anchor and modifying the instrumented bolt installation procedure to eliminate the bending effects. The elimination of bolt bending was achieved by the design and field application of an 8.5-in. (216-mm) hole facing tool. The modified instrumented bolt assembly and bolt installation procedure allowed bolt tension measurement under field conditions up to 12,500 lbs (55.6 N) with good long-term stability and no significant impact on the bolting operation. Also, as part of this study, we assured ourselves that the installed instrumented bolt was representative of other un-instrumented bolts. The elimination of bending in the installation of conventional bolts would also enhance their operating range. Application of the facing tool to all mechanical bolt installations is recommended.