Mining Publication: Roof Bolt Response to Shear Stress: Laboratory Analysis

Recent studies by researchers from the National Institute for Occupational Safety and Health indicate that shear loading contributes significantly to failure of bolts used for rock reinforcement in coal mine roofs. Laboratory test on 17 bolts were grouted through two high-strength concrete blocks, and axial tension was applied to as much as 75% of yield strength. With the block interface acting as a failure plane, shear loads were applied to the blocks at a constant rate of displacement to the ultimate strength of the bolts. The tests characterized the relationship of axial bolt loads to shear forces across a rock bedding plane and measured the distribution of axial and bending strain along the length of the bolts. These results will improve the selection of roof reinforcement in mine areas were high shear stresses are present, thus improving the safety of miners working in these areas.