MSHA - Directorate of Technical Support A Troubleshooting Guide for
Roof Support Systems


Tensioned Rebar Bolts

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EXCESSIVE THREAD TAKE-UP DURING TIGHTENING

Possible Cause Solution
C.8 Premature Tightening Torque inhibitor too weak or instruct operator in proper installation procedure
C.9 Plate Held Too Far From Roof Instruct operator in proper installation procedure
B.5 Improper Mixing Instruct operator in proper installation procedure
C.12 Grout Length Too Short Increase grout length
B.7 Hole Too Short Drill hole 1" longer than the bolt length
B.9 Cracks In Roof Increase grout volume to make up for lost grout or adjust anchorage zone
A.3 Applied Torque Too High Adjust bolter torque setting
B.4 Improper Hole-Deformed Bar Size Do not exceed manufacturer's recommended grout annulus
C.6 Poor Strata-Anchorage Exceeded Increase grout length or try different support system
B.15 Smooth Hole Change bits or vary drilling parameters

EXCESSIVE BLEED OFF

Possible Cause Solution
C.8 Premature Tightening Instruct operator in proper installation procedure
C.12 Grout Length Too Short Increase grout length or try different support system
B.9 Cracks In Roof Increase grout volume to make up for lost grout or adjust anchorage zone
C.6 Poor Strata - Anchorage Exceeded Increase grout length or try different support system
B.4 Improper Hole - Deformed Bar Size Do not exceed manufacturer's recommended grout annulus
B.5 Improper Grout Mixing Instruct operator in proper installation procedure
A.3 Applied Torque Too High Adjust bolter torque setting
A.1 Excessive Thrust Adjust bolter thrust and instruct operator in proper installation procedure
A.4 Plate/Bolt Mismatch Use higher grade plate
Smooth Hole Change bits or vary drilling parameters

ERRATIC OR POOR TORQUE/TENSION

Possible Cause Solution
C.3 Residual Torque - Torque Inhibitor Replace nuts
C.4 Thread Binding If torque inhibitors are defective replace nuts. If bolt ends are sharp replace bolts
A.2 Severe Installation Angle Use angle compensation device if installation angle exceeds 5-degrees
C.10 Plate Galling Replace nuts/plates or use hardened washers
A.1 Excessive Thrust Adjust bolter setting and instruct operator in proper installation procedure
C.2 Torque Inhibitor Too Strong/Weak Replace nuts
A.23 Irregular Roof Surface Use wedges and/or cap blocks to improve surface contact
A.8 Washer Too Soft Replace washers
A.17 Plate/Washer Mismatch Replace plates/washers
C.11 Plate/Nut Mismatch Replace nuts/plates
A.9 Defective Threads Replace bolts or nuts

BOLT PULLS THROUGH PLATE

Possible Cause Solution
Severe Roof Loading If widespread determine cause and upgrade support system
A.4 Plate/Bolt Mismatch Use higher grade plate
A.2 Severe Installation Angle Use angle compensation device if installation angle exceeds 5-degrees
A.12 Plate Hole Too Large Use hardened washers or replace plates if out of specification
A.11 Defective Plate Replace plates
A.17 Plate/Washer Mismatch Replace plates or washers
C.11 Plate/Nut Mismatch Replace nuts and/or plates or use hardened washers
A.8 Washer Too Soft Replace washers
A.23 Irregular Roof Surface Use wedges and/or cap blocks to improve the surface contact or use higher grade plate
A.3 Applied Torque Too High Adjust bolter torque setting

EXCESSIVE SUBSEQUENT TORQUE

Possible Cause Solution
Severe Roof Loading If widespread and loading exceeds bolt capacity use larger diameter or higher grade bolts
C.4 Thread Binding If caused by defective threads, soft shear pins, or sharp bolt ends replace nuts and/or bolts
C.3 Residual Torque-Torque Inhibitor Replace nuts
C.2 Torque Inhibitor Too Strong Replace nuts
C.10 Plate Galling Replace nuts/plates or use hardened washers
A.3 Applied Torque Too High Adjust bolter torque setting
A.2 Severe Installation Angle Use angle compensation device if installation angle exceeds 5-degrees
A.23 Irregular Roof Surface Use wedges and/or cap blocks to improve surface contact

INSTALLED TORQUE NOT ACHIEVED

Possible Cause Solution
C.8 Premature Tightening Instruct operator in proper installation procedure or if torque inhibitor is too weak replace nuts
C.9 Plate Held Too Far From Roof Instruct operator in proper installation procedure or if torque inhibitor is too weak replace nuts
C.12 Grouted Length Too Short Lengthen the grout column or try different support system
A.3 Applied Torque Too Low Adjust bolter torque setting
A.1 Excessive Thrust Adjust bolter settings and instruct operator of proper installation procedure
B.9 Cracks In Roof Increase the grout volume to make up for lost grout or adjust anchorage zone
B.4 Improper Hole/Deformed Bar Size Do not exceed manufacturer's recommended grout annulus
C.6 Poor Strata-Anchorage Exceeded Lengthen the grout column
B.15 Smooth Hole Change bits or vary the drilling parameters

SPRINGY BOLT

Possible Cause Solution
C.2 Torque Inhibitor Too Strong/Weak Replace nuts
C.8 Premature Tightening Instruct operator in proper installation procedure
B.5 Improper Grout Mixing Instruct operator in proper installation procedure
C.4 Thread Binding Replace bolts/nuts
C.9 Plate Held Too Far From Roof On Installation Instruct operator to hold the plate closer to the roof as recommended by the manufacturer
B.7 Hole too Short Hole length should be 1" longer than the bolt length
C.3 Residual Torque-Torque Inhibitor Replace nuts
A.3 Applied Torque Too High Adjust bolter torque

PLATE FAILS AFTER INSTALLATION

Possible Cause Solution
A.4 Plate/Bolt Mismatch Use higher grade plate
Severe Roof Loading If widespread determine cause and upgrade support system
A.23 Irregular Roof Surface Use wedges and/or cap blocks to improve surface contact or use higher grade plate
A.2 Severe Installation Angle Use angle compensation device if installation angle exceeds 5-degrees
C.11 Plate/Nut Mismatch Replace nuts and/or plates
A.17 Plate/Washer Mismatch Replace washers and/or plates
A.12 Plate Hole Too Large Use hardened washers or replace plates if out of specification
A.11 Defective Plate Replace plates

EXCESSIVE INSTALLED TORQUE

Possible Cause Solution
A.3 Applied Torque Too High Adjust bolter torque setting
C.4 Thread Binding If caused by defective threads, soft shear pins or sharp bolt ends, replace nuts and/or bolts
C.2 Torque Inhibitor Too Strong Replace nuts
C.3 Residual Torque-Torque Inhibitor Replace nuts
C.10 Plate Galling Use hardened washers or replace nuts and/or plates
A.2 Severe Installation Angle Use angle compensation device if installation angle exceeds 5-degrees
A.23 Irregular Roof Surface Use wedges and/or cap blocks to improve surface contact

BOLT BREAKS ON INSTALLATION

Possible Cause Solution
A.3 Applied Torque Too High Adjust bolter torque setting
A.2 Severe Installation Angle Use angle compensation device if installation angle exceeds 5-degrees
B.2 Defective Bolt Replace bolts
A.23 Irregular Roof Surface Use wedges and/or cap blocks to improve the surface contact or use higher grade or larger diameter bolts
A.9 Defective Threads Replace bolts
C.2 Torque Inhibitor Too Strong Replace nuts
C.4 Thread Binding If caused by defective threads, soft shear pins, or sharp bolt ends replace nuts and/or bolts

PLATE FAILS ON INSTALLATION

Possible Cause Solution
A.3 Applied Torque Too High Adjust bolter torque setting
A.4 Plate/Bolt Mismatch Use higher grade plate
A.23 Irregular Roof Surface Use wedges and/or cap blocks to improve surface contact or use higher grade plate
A.11 Defective Plate Replace plates
A.12 Plate Hole Too Large Use hardened washers or replace plates if out of specification
A.17 Plate/Washer Mismatch Replace washers and/or plates
C.11 Plate/Nut Mismatch Replace nut/plate or use hardened washers

LOW ANCHORAGE

Possible Cause Solution
C.12 Grout Length Too Short Increase grout length or try different support system
B.4 Improper Hole-Deformed Bar Size Do not exceed manufacturer's recommended grout annulus
B.15 Improper Mixing Instruct operator in proper installation procedure
B.9 Cracks In Roof Increase grout volume to make up for lost grout
C.8 Premature Tightening Instruct operator in proper installation procedure
C.6 Poor Roof Strata-Anchorage Increase grout length or vary anchorage zone
B.15 Smooth Hole Change bits or vary drilling parameters

LOOSE PLATE

Possible Cause Solution
C.2 Torque Inhibitor Too Strong/Weak Replace nuts
C.9 Plate Held Too Far From Roof On Installation Instruct operator in proper installation procedure
C.8 Premature Tightening Instruct operator in proper installation procedure
B.5 Improper Mixing Instruct operator in proper installation procedure
B.7 Hole Too Short Drill hole 1" longer than the bolt length
A.3 Applied Torque Too Low Adjust bolter torque setting

THREAD TAKE-UP DURING MIXING

Possible Cause Solution
C.2 Torque Inhibitor Too Weak Replace nuts
B.5 Improper Mixing Instruct operator in proper installation procedure
C.1 Bent Bolt Straighten bolt completely after bending or use nuts with stronger torque inhibitor
B.14 Crooked Hole Instruct operator in proper drill alignment while drilling
C.7 Viscous Grout Replace grout or use nuts with stronger torque inhibitor

NUT THREADS STRIP OUT

Possible Cause Solution
C.5 Limited Thread Engagement Replace nuts
C.4 Thread Binding Replace nuts
C.2 Torque Inhibitor Too Strong Replace nuts
A.9 Defective Threads Replace bolts or nuts

BOLT BREAKS IN BEND

Possible Cause Solution
B.12 Excessive Bolt Bending Instruct operator not to bend bolts more than 60-degrees and never more than 90-degrees
C.12 Grout Length Too Short The grout length should be long enough to completely encapsulate the notch or coupled bolts should be used
B.2 Defective Bolt Replace bolts

TORQUE INHIBITOR DOES NOT BREAK

Possible Cause Solution
C.2 Torque Inhibitor Too Strong Replace nuts
C.9 Premature Tightening Instruct operator in proper installation procedure
B.5 Improper Mixing Instruct operator in proper installation procedure
C.12 Grout Length Too Short Increase grout length
A.3 Applied Torque Too Low Adjust bolter torque setting
B.4 Improper Hole-Deformed Bar Size Do not exceed manufacturer's recommended grout annulus
C.6 Poor Strata-Anchorage Exceeded Increase grout length
B.9 Cracks In Roof Increase grout volume to make up for lost grout or change anchorage zone
B.15 Smooth Hole Change bits or vary drilling parameters
C.4 Thread Binding If caused by defective threads, soft shear pins, or sharp bolt ends replace nuts and/or bolts

WASHER BADLY DEFORMED

Possible Cause Solution
A.2 Severe Installation Angle Use angle compensation device if installation angle exceeds 5 degrees
Severe Roof Loading If widespread determine cause and upgrade support system
A.17 Plate/Washer Mismatch Replace washers or plates
A.12 Plate Hole Too Large Use hardened washers or replace plates if out of spec.
A.23 Irregular Roof Surface Use wedges and/or cap blocks to improve surface contact or use a higher grade plate
A.3 Applied Torque Too High Adjust bolter torque setting
A.8 Washer Too Soft Replace washers

WASHER CRACKS

Possible Cause Solution
A.8 Washer Too Hard Replace washers
A.2 Severe Installation Angle Use angle compensation device if installation angle exceeds 5 degrees
A.12 Plate Hole Too Large Replace plates
A.23 Irregular Roof Surface Use wedges and/or cap blocks to improve surface contact or use higher grade plates
A.17 Plate/Washer Mismatch Replace plates or washers