ICGCM Papers:
New Ground Control Product Developments
 
 
System Behavior of Roof Bolt Systems with Varying Bearing Plate / Angle Compensating Device Combinations
35th International Conference on Ground Control in Mining
System Behavior of Roof Bolt Systems with Varying Bearing Plate / Angle Compensating Device Combinations
by
Gregory E Smith, Engineered Mine Solutions, LLC, Lebanon, United States
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[Conference] 35th International Conference on Ground Control in Mining
[Price] Free  [Comments] 0
[Topical Area] New Ground Control Product Developments
[Author] Gregory E Smith, Engineered Mine Solutions, LLC, Lebanon, United States
[Abstract] 
Key Conclusions:
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The Mine Ground Support Design Engineer should test the total support system to understand its profile, capacity, and failure modes. This system behavior should be input into the support design in addition to the individual component specifications as mandated in 30CFR part 75 and detailed in document ASTM F432. By varying different ASTM F432 grade 3 plate / angle compensating device combinations, the system behavior and failure modes can be significantly altered. A system using a new plate / angle compensating device combination improves system behavior, capacity, and offers material savings and other operational benefits.
Key Findings:
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A load versus deformation study was conducted using a common 7/8" bolt and varying the grade 3 plate / angle compensating device combinations to accommodate a 1-3/8" diameter mechanical anchor. Each system was tested by testing the bolt at right angles to the simulated roof plane and at an off-set angle of 10 degrees. All (3) combinations studied exhibited different load deformation profiles as well as different failure modes. Only (1) system was able to achieve the minimum bolt ultimate strength. In another test conducted at Bruceton, (2) of the systems were compared. The results showed similar system profiles and, again, only the new system was able to achieve the minimum bolt ultimate strength rating. This system achieved actual bolt failure in all tests, averaging over 63,000 lbs.
Objective of the Paper:
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The objective of this paper is to study the load versus deformation profile and failure mode of (2) different commonly used tensionable bolt systems and to introduce an alternative plate / angle compensating device combination that greatly improves the behavior and overall capacity of the system.
Problem Statement:
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Tensionable headed roof bolt systems are common in the US. Many of these systems utilize a mechanical anchor to develop tension as well as a bearing plate and spherical washer to comply with the requirements of 30CFR 75.204(f)(8). This regulation mandates that an angle compensating device be used in tensionable systems when the bolt is installed at an angle greater than 5 degrees from the plane of the bearing plate. For several reasons, the manufacturer often supplies the bolt with the washer and mechanical anchor assembled. The bearing plate is then supplied with a center hole large enough to allow it to slip over the anchor prior to installation. The bearing plate is often a dome or volcano style plate. In these systems, the load versus deformation profile and failure mode need to be identified to properly design the support system. It is common in these systems for the failure mode to be at the plate and at loads much less than the minimum ultimate strength of the bolt.