Axial Performance of Cable Bolts Under Various Bonding and Loading Conditions

Axial Performance of Cable Bolts Under Various Bonding and Loading Conditions

Cable bolts are one of the main methods of support for many mining and civil engineering projects. This study focused on the axial performance of the cable bolts under various conditions. A large scale pull out apparatus was designed to support the testing of various mainstream cables in the Australian mining industry. An additional small scale test was also devised to provide comparative results with the large scale test. Six cable types, ranging from plain to indented and bulbed, were encapsulated using two types of cementitious and resin based bonding agents. The cables were first tested in each testing scale in monotonic and cyclic loadings to simulate varying stress paths for the service life performance of the cables. The results showed much higher stiffness for the large scale tests compared to the small scale sleeve pull out tests. All grouted cables consistently illustrated higher load values in all tests compared to the resin sample. The bulbed cable indicated that the presence of a bulb structure on a cable tends to overshadow other attributes. Cyclic tests in both testing setups suggested a low to almost non-existing adverse effect on the pull out test compared to the monotonic tests. Surface indentation clearly increased the performance of the cable bolts in all cases. The radial stiffness value on the large scale tests was a determining factor. In the end, a series of numerical models using finite element was calibrated by the results of the large scale tests. The sensitivity analysis of the numerical model exhibited a similar effect for the elastic modulus of confinement and the uniaxial compressive strength of the concrete and grout for plain and bulbed cables. Finally, in the numerical model, the most important factor proved to be the bulb size; with a high potential to alter the load values with even small changes.

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