B.1 DEFECTIVE GROUT
To determine if the grout is defective cut open a cartridge and push out a
small amount of the grout and catalyst. Next thoroughly mix the grout by hand.
If the grout does not harden within the manufacturer's gel time it could be
defective. Next, install a bolt with just enough resin to grout two feet. After
allowing the grout to cure for 5 minutes apply 150 ft.-lbs. to the bolt head
with a torque wrench. If the bolt head rotates the grout should not be used
until the manufacturer has tested it.
B.2 DEFECTIVE BOLT
Defective bolts can result in premature bolt failure. Only notched rebar can
be field tested easily. If the bolts are breaking in the notched area, take a
bolt and bend it 90-degrees then straighten it. Inspect the notch for cracks. If
no cracks are visible then the notch itself is good, however, the strength of
the notch should also be checked. This can be accomplished by performing a pull
test provided enough anchorage is available to break the bolts. The pull test
should be conducted by installing the bolt with enough material to grout the
bolt above the notch. Next, pull the bolt to failure. The notch strength should
be a minimum of 23,000 lbs. A pull test could also be conducted to check the
strength of a full diameter bolt in the same manner by partially grouting the
bolt. When checking the bolts underground it is not necessary, nor recommended
to break the bolts. Loading the bolts to the minimum ultimate is sufficient
since most bolts have breaking loads in excess of the minimum. If the pull test
cannot be conducted at the mine, the bolts should be sent to a testing lab for
evaluation.
B.3 IMPROPER GROUT CARTRIDGE
It is important to use the correct grout cartridge and installation procedure
to ensure a successful installation. Always check the box that the cartridges
came in for information regarding the proper application of the grout e.g.,
borehole size, cure rate, equivalent length, etc. If grout cartridges are found
outside of the box or if the label identifying the product is missing the
cartridges should not be used.
B.4 IMPROPER HOLE - DEFORMED BAR SIZE
If the deformed bar and hole diameter are not sized correctly, the grout
annulus will not be within the manufacturer's recommendations and can result in
a poor installation. Check the borehole diameter at various points along the
length. If the hole diameter is good the problem could be due to the type of
deformed bar being used. Some specialty deformed bar are rolled specifically for
a particular manufacturer. Often these types of deformed bar are of a smaller
diameter than standard rebar and might need some adjustment in the installation
e.g., additional resin or smaller diameter holes.
B.5 IMPROPER MIXING
Improper mixing affects the installation by causing the grout to cure too
fast or too slow. If you suspect that the grout is not being mixed properly have
the operator install several bolt as you observe the procedure and time the
mixing cycle. If the operator is not following the manufacturers installation
procedures, go over the procedure and install several more bolts to see if the
problem has been corrected.
B.6 TEMPERATURE TOO HOT/COLD
If the grout cartridges are too cold they may become too hard which would
make penetration of the cartridges difficult or in some cases may prevent
complete insertion of the bolts. Cold temperatures may also require longer
mixing time to generate more heat to ensure proper curing. Hot temperatures will
cause the grout to cure more rapidly. In this case reducing the mixing times can
slow down the cure rate. When long bendable bolts are used hot temperatures may
cause the grout to cure before the bolt is fully inserted. When this occurs a
slower curing grout should be used. Tests should be conducted to determine the
cure rate needed.
B.7 HOLE TOO SHORT/LONG
Measure the borehole length. Generally the hole length for fully grouted bolt
installations are drilled 1" longer than the bolt length.
B.8 HOLE DIAMETER TOO LARGE/SMALL
Hole diameter can vary in hard or soft strata. Check the hole diameter along
the borehole length. If the hole diameter is not within the manufacturer's
tolerance check the drill bit dimensions which should be within plus or minus
0.030-inch of the recommended hole diameter.
B.9 CRACKS IN ROOF
After checking all the other possibilities e.g., hole diameter, hole length,
etc. the next step should be to check the borehole for cracks with a
strata-scope. Any cracks can be a source of grout migration out of the borehole.
B.10 EXCESS ROTATION DURING INSERTION
In some applications especially when using long bolts, excessive rotation
during insertion can cause the grout to cure before the bolt and plate have
contacted the roof. To determine if excessive rotation is causing the problem,
have the operator install several bolts with as little rotation as possible
during insertion. If this remedies the problem, then instruct the operator to
continue installing the bolts in a similar manner.
B.11 EXCESSIVE THRUST DURING MIXING
Applying thrust to the bolt head during the mixing cycle is unnecessary and
can cause excessive heat build up and sparking, both of which are possible ignition
sources. Before installing any more bolts, make sure that the operator is not
using the drilling settings during the installation of the bolts. If sparking,
smoke, or a hot bolt head occur during the mixing cycle, then the bolter thrust
setting is too high. Reset the bolter thrust and instruct the operator not to
apply thrust while mixing.
B.12 EXCESSIVE BOLT BENDING
Excessive bolt bending can cause the formation of cracks in the notched area
resulting in a significant loss of bolt strength. Observe the operator to see
how the bolts are being bent. In general the bolts should not be bent more than
60-degrees and never more than 90-degrees.
B.13 EXCESSIVE TORQUE APPLIED
When making a torque check on a non-tensioned grouted bolt never apply more
than 150 ft.-lbs. Applying more than 150 ft.-lbs. could twist off the bolt head
or destroy the grout anchor. If the bolt head rotates at 150 ft.-lbs. then the
installation is no good and another bolt should be installed.
B.14 CROOKED HOLE
To check if crooked holes are causing the problem insert a bolt without
grout. If the bolt cannot be fully inserted, or resistance is felt, then the
hole is crooked. Instruct the operator to be more careful of the bolter
alignment while drilling.
B.15 SMOOTH HOLE
In rare situations drilling in some strata produces an extremely smooth hole
which results in very poor anchorage. If this problem is encountered, try
changing to a different type of drill bit. If the problem persists next try
varying the bolter thrust and/or rotation.
B.16 SHELF LIFE EXCEEDED
When the shelf life of the grout is exceeded the cartridges can become hard
which affects the workability of the grout and possibly the anchorage of the
support. If the shelf life is exceeded, the grout should be discarded or should
be analyzed by the manufacturer.
B.17 STORAGE TEMPERATURE TOO HOT
Storing grout in a hot environment affects shelf life and the cure time.
Grout manufacturers have recommended storage requirements for their grout which
should be followed.
B.18 BOLTING MACHINE ON DRILLING SETTINGS
Most bolting machines have two settings, one for drilling the holes and one
for installing the supports. It is important that the machine is on the correct
setting for proper bolt installations.
