6
from the one bolt by hammering. I suspect that this
was because the bolts only had residual resin in the
mid and deep span portions of the bolt. The more
recent incidents of a failed bolts not holding weight
and a poor pull test on the 69 level have led us to
suggest more must be done to protect the entire bolt.
A GWO (geotechnical work order) was issued in
October 2022 after a resin anchored bolt in the TPL2
Pump Room that was to be used as part of the rigging
to change piping in the pump room began to move and
started to come out of the hole with very minimal effort.
Water has coming out of the hole, and approximately
2 feet of the bolt at the collar was shown not to have resin.
Subsequently a bolt just above that bolt failed a pull test of
only 7 tons (minimal to be 15 tons). The area was subse-
quently rehabbed with 8 bolts on 4 bolt per row pattern to
insure ground support. Both bolts were pulled out intact
and were sent to a material testing facility and a report gen-
erated (PNL, 2023).
PNL Test Results
The conclusions were that the two bolts were either not
fully encapsulated or properly installed initially in October
2020. It also brings up the difficulty in installation of bolts
with the current cartridge package resin systems and jack-
legs. The presence of large amounts of hot water in weaker
ground may also affect resin-bondage when mixing. The
greatest loss in cross-sectional area was found in the #2 bolt
(0.50 in2) and yields a corrosion rate of 0.042 in2/yr. The
average cross-sectional loss of 0.54 in2 (which was consis-
tent on both bolts samples examined) yields a corrosion
rate of 0.022 in 2/yr (see Figure 11). Based upon these
values, the bolts are estimated to fall below the minimum
pull strength at approximately 6 years for minimum and 12
years for average corrosion.
No evidence of any epoxy resin encapsulation was
observed on any of the lengths of bolts provided for analy-
sis. The corrosion pattern is suggestive of a leak path that
existed around the bolt. The isolated leak path allowed for
the first 1–4 feet of the galvanized coating to be attacked
and allowed for pitting corrosion to initiate. The surface
adjacent to the pits showed notable galvanized coating still
present to varying thicknesses.
Partial Bolts
In addition to the two whole length bolts that were tested,
5 bolts were over cored, but only the first 1–2' were recov-
ered. All 5 holes were difficult to properly over core, even
with dip angle and bolt alignment techniques. There may
be several reasons for this such as using the wrong drill, or
seemingly bent bolts in the first few feet. We may need to
specialize in a portable drill rig specifically for overcoring.
There was no evidence any visible resin encapsulation on
the surface of any of the samples received
CORROSION PROTECTION SELECTION
Figure 12 is a diagram from Preston and others (2019)
that shows the relative corrosion resistance versus elonga-
tion capacity. It emphasizes the use of grouted or resin fully
encapsulated bars as providing the most resistive to corro-
sion. The grout or resin provides a barrier between the steel
and the mine water. Encapsulation using grout is shown as
Figure 10. Corrosion loss for rebar bolts, and photos sample
36195 showing near anchor, mid-anchor and deep end
corrosion from (CTL, 2019) bolt tests
Figure 11. Graphical plot of load capacity vs time for 2
resin rebar bolts in 68L Pump Room based upon calculated
corrosion rates (from PNL, 2023)
from the one bolt by hammering. I suspect that this
was because the bolts only had residual resin in the
mid and deep span portions of the bolt. The more
recent incidents of a failed bolts not holding weight
and a poor pull test on the 69 level have led us to
suggest more must be done to protect the entire bolt.
A GWO (geotechnical work order) was issued in
October 2022 after a resin anchored bolt in the TPL2
Pump Room that was to be used as part of the rigging
to change piping in the pump room began to move and
started to come out of the hole with very minimal effort.
Water has coming out of the hole, and approximately
2 feet of the bolt at the collar was shown not to have resin.
Subsequently a bolt just above that bolt failed a pull test of
only 7 tons (minimal to be 15 tons). The area was subse-
quently rehabbed with 8 bolts on 4 bolt per row pattern to
insure ground support. Both bolts were pulled out intact
and were sent to a material testing facility and a report gen-
erated (PNL, 2023).
PNL Test Results
The conclusions were that the two bolts were either not
fully encapsulated or properly installed initially in October
2020. It also brings up the difficulty in installation of bolts
with the current cartridge package resin systems and jack-
legs. The presence of large amounts of hot water in weaker
ground may also affect resin-bondage when mixing. The
greatest loss in cross-sectional area was found in the #2 bolt
(0.50 in2) and yields a corrosion rate of 0.042 in2/yr. The
average cross-sectional loss of 0.54 in2 (which was consis-
tent on both bolts samples examined) yields a corrosion
rate of 0.022 in 2/yr (see Figure 11). Based upon these
values, the bolts are estimated to fall below the minimum
pull strength at approximately 6 years for minimum and 12
years for average corrosion.
No evidence of any epoxy resin encapsulation was
observed on any of the lengths of bolts provided for analy-
sis. The corrosion pattern is suggestive of a leak path that
existed around the bolt. The isolated leak path allowed for
the first 1–4 feet of the galvanized coating to be attacked
and allowed for pitting corrosion to initiate. The surface
adjacent to the pits showed notable galvanized coating still
present to varying thicknesses.
Partial Bolts
In addition to the two whole length bolts that were tested,
5 bolts were over cored, but only the first 1–2' were recov-
ered. All 5 holes were difficult to properly over core, even
with dip angle and bolt alignment techniques. There may
be several reasons for this such as using the wrong drill, or
seemingly bent bolts in the first few feet. We may need to
specialize in a portable drill rig specifically for overcoring.
There was no evidence any visible resin encapsulation on
the surface of any of the samples received
CORROSION PROTECTION SELECTION
Figure 12 is a diagram from Preston and others (2019)
that shows the relative corrosion resistance versus elonga-
tion capacity. It emphasizes the use of grouted or resin fully
encapsulated bars as providing the most resistive to corro-
sion. The grout or resin provides a barrier between the steel
and the mine water. Encapsulation using grout is shown as
Figure 10. Corrosion loss for rebar bolts, and photos sample
36195 showing near anchor, mid-anchor and deep end
corrosion from (CTL, 2019) bolt tests
Figure 11. Graphical plot of load capacity vs time for 2
resin rebar bolts in 68L Pump Room based upon calculated
corrosion rates (from PNL, 2023)