Department of Labor
Mine Safety and Health Administration
EXPANSION SHELL/RESIN ASSISTED ROOF BOLT ALERT
A mine in District 8 recently
experienced several roof falls on a working section panel.
Several roof bolts were recovered from one of the falls and
inspected. The bolts were expansion shell/resin assisted type
bolts using a jam nut. The bolts recovered had severely twisted
shells with the leaves buckled inward onto the threads. Although
some geologic conditions had an impact on the deteriorated roof
conditions in the area, the distorted shells on the bolts may
have significantly contributed to the roof falls.
The roof bolts used a standard expansion shell with a jam
nut and were installed with 2 feet of resin. Tests have shown
that when the jam nut is too strong, the nut will not strip off
and the expansion shell will then twist and deform during
tensioning of the bolt. The results are low tension/torque ratio,
shell distortion, high thread tension, or some combination of
these. When this occurs the bolt is not functioning properly. For
expansion shell/resin assisted bolts, the jam nut should have a
breaking torque less than or equal to the installed torque of the
- Make sure products received from manufacturers are certified
as meeting all applicable ASTM specifications as stated in 30 CFR
§ 75.204. Jam nuts should not interfere with the proper
tensioning of the bolt.
- Check roof bolting machines for proper torque settings.
Abnormally high torque may also add to the problem of distorted
- Re-instruct roof bolting machine operators as to proper
installation procedures, such as proper drill hole depth, resin
cartridge length, and installed torque. Follow the manufacturer's
If you would like further information on this subject, please
contact the MSHA District Office at 812-882-7617.
Please post this alert notice in a conspicuous location
at the mine.
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This information was provided by concerned
miners in an effort to eliminate accidents. Accident or "close
call" information within District 8 may be shared by contacting
the MSHA office at (812) 882-7617.