Over the last 20 years, roof support technology has made numerous advances since the original wedge and slotted bolts of the 1950's. By comparison, the roof supports used today are more complex and specialized than the supports used in the past, providing mines with a varied selection of supports from which to choose. As a result, when problems with supports are encountered, it is more difficult to determine whether it is the result of geological changes, poor installation practices, or malfunctioning supports.
The purpose of this guide is to provide a logical sequence to resolving the most common problems encountered with roof supports. The information contained in this guide was originally published as MSHA IR 1237. The authors are Raymond A. Mazzoni, George J. Karabin, and Joseph A. Cybulski.
To simplify the troubleshooting procedures, roof supports are classified into five categories to make it easier to emphasize problems that are unique to a particular support type:
| 1. | Mechanical Bolts |
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Bolts using an expansion anchor without resin. | |
| 2. | Fully Grouted Bolts |
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Non-tensioned, headed rebar. | |
| 3. | Tensioned Rebar Bolts |
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Threaded deformed bar using a grout anchor and tension nut. | |
| 4. | Point/Combination Anchored Bolts |
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Two-piece bolts using a grout anchor and a tensioning coupler without an expansion anchor. | |
| 5. | Mechanically Anchored Resin-Assisted Bolts | Tensioned grouted bolts using expansion anchors. |
The problems and probable causes listed in each category are the result of data accumulated from years of laboratory and field investigations. The troubleshooting tips are quite comprehensive, but due to the many variables affecting strata control are not intended to address every conceivable problem that might be encountered.