Behaviour of cable bolts in shear: experiment and mathematical modelling
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The application of cable bolts for ground support is increasing in underground coal mines worldwide. Currently, two methods of evaluating the performance of the cable bolt are favoured: the short encapsulation pull test, and the shear test. The former method can be used both in the laboratory and in the field while the latter can be undertaken mainly in the laboratory. There are two methods of shear strength testing: single and double shear tests. This paper examines the double shear testing of several cable bolts currently marketed in Australia under various pre-tension stresses. Both plain and indented wire cable bolts were tested. It was found that the shear strength of the cable bolt was a function of the wire geometry and initial pre-tension. Indented wire cable bolts were lower in shear strength than the plain wire cable bolts. A mathematical model was proposed to evaluate the shear strength of cable bolts using Fourier series and a linear relationship between shear and normal loads. The model coefficients were determined based on the experimental results. The findings from the mathematical modelling tallied well with the experimental results.