DESIGNING A ROCK BOLTING SYSTEM

Special Research Report SR-73 Studies revealed that a considerable cost reduction was possible by suspending a monorail transportation system on roof bolts. One such system has been installed at the Thirty-Slope Mine Inc., St. Clair, Pennsylvania and studied under production conditions. The performance of rock bolts is of paramount importance in such an installation. Although research has been conducted for a number of years, perfor- mance was further evaluated by static and dynamic tests. Bolts of two different lengths equipped with four variations of anchorage devices were studied to establish basic data pertaining to economy and safety. Forty-two inch long bolts with expansion shells and resin packages were selected to suspend the system. In addition to field studies, analytical analyses were attempted to discover the important parameters affecting bolt performance. The parameters considered were: compressive strength, internal friction of rock, and the geometry of serration. The effects of these parameters were presented in dimensionless form, indicating that inverted serra- tions and increased internal friction angles gave better performance. It was also noted that initial rapid loss of bolt load was due to too closely spaced serrations.