Rock bolting and pull out test on rebar bolts
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Pull out tests were carried out in the laboratory of rock mechanics at Norwegian University of Science and Technology (NTNU) for the purpose of determining the critical embedment length of fully grouted rebar bolts. The 20-mm rebar bolts and the grouting material, the Rescon Zinc bolt cement used in the testing are widely used in underground projects in Norway. Different embedment lengths, ranging from 10 cm to 40 cm, were employed in the tests under different water-cement ratios for the grouting mortar. The critical embedment length for a given water-cement ratio is determined on the diagram of the pull - out load versus the embedment length. A chart of the critical embedment bolt length versus the water-cement ratio as well as the uniaxial compressive strength of the cement mortar is established based on the testing results. In the theoretical part of the thesis, the main focus is on rock bolting. Bolting principals are introduced along with different types of rock bolts, design of bolting systems and stability problems caused by rock stresses. In the final part of the theoretical part the procedure of pull out testing is described and the load bearing capacity of rock bolts are categorized into the groups in accordance with load deformation performance. Finally, previous pull out test research is presented.