U.S. Department of Labor

Mine Safety and Health Administration 1100 Wilson Boulevard Arlington, Virginia 22209-3939

FROM:           MARK E. SKILES
                        Director of Technical Support

                        RAY McKINNEY
                       Administrator for
                            for Coal Mine Safety and Health



SUBJECT:      Tensioned Cable Bolts

Scope
This Procedure Instruction Letter (PIL) applies to Coal Mine Safety and Health (CMS&H) District Managers and coal mine enforcement personnel.

Purpose
This PIL establishes procedures to evaluate Tensioned Cable Bolts for use as required support for compliance with Title 30 Code of Federal Regulations (30 CFR) § 75.204(b) and 75.221(a)(9).

Procedure Instructions
CMS&H District Managers shall evaluate requests for approval of Tensioned Cable Bolts used as required support as follows:

     Component Tests: Laboratory tests should be conducted to determine the strength and compatibility of all of the individual components of the cable bolts. Any components covered by ASTM F432-95 must meet those specifications. The manufacturer should specify all other components. Any changes to the original components or additional components added to the support would warrant additional testing. Once a specific design has been successfully tested, no further testing should be required unless the quality of the components is suspected of being inferior.

     Installation Procedure: Roof bolter operators should be trained in safe handling and proper installation techniques. In-mine testing should be conducted to determine if the supports can be installed safely and reliably. These tests should ensure that the safety of the operator is not jeopardized during the handling and installation of the tensioned cable bolts.

     Pull Tests: Underground pull tests should be completed to determine the anchorage capacity and displacement characteristics of the support for the anchor length used. If the anchor length or type is modified, additional anchorage tests should be conducted.

     Tension Tests: Underground tests should be conducted to determine the installed load range of the supports and verify that the tension level can be achieved and maintained as required in 30 CFR § 75.204(f). These tests should be done with a load-measuring device that is capable of indicating the installed load of the support. Any anomalies that occur during the test, e.g. spring-back, should be noted in order to determine the effect on the installed load and the ability to comply with the regulations.

     Test Area: Depending on the district's experience with tensioned cable bolts as required support and the roof conditions at a specific mine, a test area may be warranted. If deemed necessary, a test area could be established to demonstrate the effectiveness of the tensioned cable bolts. A test area can range from an area of the mine where a number of bolts are installed for observational purposes up to a fully instrumented area monitoring roof sag and bolt loading.

Based on District experience with the test area, the District could then review the tests or demonstration results of the bolts at the mine for possible inclusion in the mine's roof control plan.

The Mine Safety and Health Administration shall require that tensioned cable bolts, approved as required support, have specifications in the roof control plan. Presently, there are no ASTM or nationally recognized specifications for tensioned cable bolts used in underground mines. Also, some manufacturers have multiple designs of tensioned cable bolts. Listing a specification in the roof control plan would eliminate any confusion between the District and the mine operator regarding the approval of a particular tensioned cable bolt. This specification should include the following:

• Each component of the system should be specified including all dimensions. For example, if a threaded tube is used, the tube length, tube thread strength, and thread length should be listed.



• A drawing depicting all components used with the system. This drawing should show the location of each component.



• For the cable itself, the plan should have a specification that includes the type of strand, e.g. 7-strand epoxy coated, a minimum strength requirement, and the head/housing should be capable of breaking the cable without failing.



• Each cable bolt should have a marking to identify the length, manufacturer, and type of cable (epoxy, galvanized, or etc.).



• Minimum resin cartridge length (actual length of the cartridge and not the grouted length), cartridge diameter and hole diameter should be listed.



• The installation procedure and remedial action if a bolt is improperly installed. For example, if the bolt is not properly tensioned, the head sprung back, or a spinner occurs, then another bolt should be installed.



• Tension range and a method of determining it in order to comply with 30 CFR § 75.204(f)(4) of the regulations. Also, a procedure should be established to verify this method.