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The function of roof bolts and a new device for underground roof stabilisation Karara, Said Mahmoud

Abstract

Investigations were carried out to reach a comprehensive understanding of the action of the roof bolt together with its anchor, on the rock, and how this action helps in stabilising the roof in underground openings. Tests were conducted on a two dimensional photoelastic epoxy model, as well as on a limestone rock model. Results and their analysis revealed that, with the present design of the roof bolt, the most effective type of anchor is the one with the lowest-transverse force. Thus, the glue-anchored bolts are more effective than the expansion shell anchored ones. It was found that the expansion-shell-anchored bolts give high lateral compressive stresses around the anchor, longitudinal compressive stresses along the effective length of the bolt, and tensile lateral stresses in between the end bearing plates. The epoxy anchored standard bolts give no significant transverse compressive stresses around the anchors, nor between them, longitudinal compressive stresses along the effective length of the bolt, and lateral tensile stresses inbetween the end bearing plates. In practical application, the limitations imposed by present rock bolt designs inhibit the attainment of stress distribution patterns in accord with theoretical roof stabilisation principles. To increase the bolt efficiency in stabilising the roofs, a compressive device was found very useful in adding lateral compression to the surrounding stress field. This device can be used alone or fitted to rock bolts to induce compressive lateral stresses in zones where such stresses might help to form a stable roof.

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