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Abstract of the Article

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A laboratory study on bond failure mechanism in rock bolts using a modified Hoek cell

Authors:
[ Mahdi Moosavi ] - Assistant Professor, Mining Engineering Dept., Faculty of Engineering, The University of Tehran, Tehran, Iran
[ Ahmad Jafari ] - Assistant Professor, Mining Engineering Dept., Faculty of Engineering, The University of Tehran, Tehran, Iran
[ Arash Khosravi ] - Graduate student, Mining Engineering Dept., Faculty of Engineering, The University of Tehran, Tehran, Iran

Abstract:

The stability of underground excavations during and after construction is the main concern of geomechanical design engineers. Rock masses contain natural discontinuities, which may cause stability problems, therefore most underground openings need to be stabilized to maintain their integrity during their service life. The best way to achieve this is through the use of reinforcement to help maintain the load-carrying capability of rock masses near excavation boundaries. Rock bolt is the most widely used type of reinforcement in rock engineering projects. Although numerous research on the bond capacity of a bolt is available but the detail study of the bond failure mechanism in this type of reinforcement has yet to be done. The main component of the bond capacity in rock bolts is mechanical interlocking, which after onset of slip, mobilizes the shear strength of the grout against the steel ribs. Similar to any rough interface, the most important factors controlling the shear strength at bolt-grout interface are confining pressure and grout properties. Many examples exist in which a properly performed bolt at initial stages of installation has failed later due to stress decreases caused by nearby excavations. To study the pressure dependency of bond strength of a deformed bar, a modified triaxial Hoek cell was designed to facilitate application of a radial confining pressure to a grouted bolt while pulling it axially. During the test, both axial displacement of the bolt as well as the radial dilation of the grout was monitored. While pull out, the cement that is captured between lugs will shear which in turn emphasizes the importance of shear strength of the grout annulus. In this paper, details of the laboratory test results are presented and conclusions are given based on the obtained results.

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