ICGCM Papers:
Fundamental Research Studies
 
 
The Load Transfer Properties of Post-Groutable Cable Bolts Used in the Australian Coal Industry
31st International Conference on Ground Control in Mining
The Load Transfer Properties of Post-Groutable Cable Bolts Used in the Australian Coal Industry
by
Rob Thomas, Strata Engineering (Australia) Pty Ltd, Charlestown, Australia
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[Conference] 31st International Conference on Ground Control in Mining
[Price] Free  [Comments] 0
[Topical Area] Fundamental Research Studies
[Author] Rob Thomas, Strata Engineering (Australia) Pty Ltd, Charlestown, Australia
[Abstract] 
Problem Statement:
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Adequate load transfer is considered essential for optimum ground support and is increasingly important in weak roof and/or high stress environments. If adequate load transfer is achieved not only can this have a positive impact on the resulting roof behaviour but may also allow the use of lower and hence more economic densities of roof support. A wide variety of post-groutable cable bolts are currently in use in the Australian coal mining industry, each of varying capacity, design and grouting methodology. Whilst all of the cables are supplied with the appropriate steel specification, strength and modulus data, critically the Australian coal mining industry does not have access to a comprehensive and comparative database on the corresponding load transfer performance.
Objective of the Paper:
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On the basis of the above, this paper describes the methodology and results of a laboratory pull testing program that aims to assess the impact of cable bolt design on load transfer and specifically, the impact on the capacity and pre and post-peak stiffness of the anchorage. Other points addressed include the details of the testing methodology used and a review of the various grouting techniques, grout types, pre-tensioning techniques and hole diameters used in the Australian coal industry. As part of the testing program, 20 cables were tested including (i) plain strand cables in hole diameters ranging from 28 to 55mm and (ii) bulbed and bird-caged cables in hole diameters ranging from 42 to 65mm. Other parameters assessed include the significance of smooth and profiled wire, individual wire diameter, wire packing, and tight and expanded geometry bird-cages.
Key Findings:
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The main results of the testing indicate that in comparison to plain strand cables, if the cable is bulbed or bird-caged, the capacity of the anchor can increase by up to 200% and the pre-peak stiffness by up to 700%. The results also indicate that hole diameter does not have a significant impact on load transfer with plain strand cables and that by increasing the hole diameter, a slight improvement in load transfer can be achieved with bird-caged cables.
Key Conclusions:
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Accepting that high load transfer is not always the main prerequisite when determining the most appropriate cable bolt type and that other factors such as pre-tension, cost and speed of installation must be taken into account, guidance is also provided as to what type of cable is most appropriate in what type of ground conditions. Lastly, consideration is also given to future potential improvements in cable bolt design including bird-cage size and frequency, hole size and grout strength.