7
curves for longer anchorage length of 0.914 m. Figure 6b
illustrates the load-displacement curves of PGPTs carried
out in Mine-C. In one of the tests, the yielding capacity of
steel rebar was reached, while in the other test, the peak load
reached approximately 83% of the yield capacity of a steel
rebar. Table 2 summarizes the key features of all conducted
PGPTs extracted from Figure 6. The anchorage capacity of
rib bolts, as determined by PGPTs, primarily relies on the
yielding of the steel rebar, irrespective of unregulated rota-
tion speeds that adopted during their installation.
Fully Grouted Pull-out Tests (FGPTs)
Pull-out tests were carried out on fully grouted bolts in
four mines. The rotation speed during bolts installation
was not regulated in all the FGPTs. These tests were con-
ducted until the bolts failed for some tests, with strict
adherence to safety protocols throughout the testing pro-
cess. Figure 7 shows the head portion of one of fractured
bolts showing the necking behavior induced during the
pull-out test. Figure 8 illustrates the load-displacement
curves of all FGPTs. Table 3 lists a summary of the key
features of all conducted FGPTs as extracted from Figure 8.
As anticipated, the load-bearing capacity of rib bolts within
all FGPTs primarily relies on the yielding characteristics of
the steel rebars, regardless of the unregulated rotation speed
employed during their installation.
In a prior investigation focused on the performance
of mechanically anchored rib bolts within underground
coal mines, significant findings highlighted the substantial
influence of coal mass strength on the observed bolt capac-
ity (Mohamed, et al., 2019).
In our ongoing research, we initially hypothesized a
similar influence of coal mass strength on the measured
capacity of resin-grouted bolts. However, our findings did
not support this hypothesis. Instead, we discovered that
coal mass strength does impact the measured stiffness of
grouted bolts, with stronger coal seams exhibiting a stiffer
bolt behavior. This observation was quite evident in MineE
when rib bolts were tested within the soft Pocahontas No. 3
coal seam.
Table 2. Key features of PGPTs for bolts with a length of 1.219 m and rebar diameter of 15.875 mm
Mine Coal Seam
Number
of Tests
Anchorage
Length (m)
Average 1st
peak load
(kN)
1st Peak
Load Range
(kN)
Average 1st Peak
Displacement
(mm)
B Pittsburgh 3 0.610 98 95–103 17
2 0.914 92 87–92 10
C Pittsburgh 2 0.686 59 40–77 6
Figure 7. Load-displacement curves for FGPTs, where solid
lines correspond to a 1.219 m bolt length and dotted lines
correspond to a 1.524 m bolt length
Figure 8. Head portion of fractured bolt
showing necking behavior induced by FGPT
curves for longer anchorage length of 0.914 m. Figure 6b
illustrates the load-displacement curves of PGPTs carried
out in Mine-C. In one of the tests, the yielding capacity of
steel rebar was reached, while in the other test, the peak load
reached approximately 83% of the yield capacity of a steel
rebar. Table 2 summarizes the key features of all conducted
PGPTs extracted from Figure 6. The anchorage capacity of
rib bolts, as determined by PGPTs, primarily relies on the
yielding of the steel rebar, irrespective of unregulated rota-
tion speeds that adopted during their installation.
Fully Grouted Pull-out Tests (FGPTs)
Pull-out tests were carried out on fully grouted bolts in
four mines. The rotation speed during bolts installation
was not regulated in all the FGPTs. These tests were con-
ducted until the bolts failed for some tests, with strict
adherence to safety protocols throughout the testing pro-
cess. Figure 7 shows the head portion of one of fractured
bolts showing the necking behavior induced during the
pull-out test. Figure 8 illustrates the load-displacement
curves of all FGPTs. Table 3 lists a summary of the key
features of all conducted FGPTs as extracted from Figure 8.
As anticipated, the load-bearing capacity of rib bolts within
all FGPTs primarily relies on the yielding characteristics of
the steel rebars, regardless of the unregulated rotation speed
employed during their installation.
In a prior investigation focused on the performance
of mechanically anchored rib bolts within underground
coal mines, significant findings highlighted the substantial
influence of coal mass strength on the observed bolt capac-
ity (Mohamed, et al., 2019).
In our ongoing research, we initially hypothesized a
similar influence of coal mass strength on the measured
capacity of resin-grouted bolts. However, our findings did
not support this hypothesis. Instead, we discovered that
coal mass strength does impact the measured stiffness of
grouted bolts, with stronger coal seams exhibiting a stiffer
bolt behavior. This observation was quite evident in MineE
when rib bolts were tested within the soft Pocahontas No. 3
coal seam.
Table 2. Key features of PGPTs for bolts with a length of 1.219 m and rebar diameter of 15.875 mm
Mine Coal Seam
Number
of Tests
Anchorage
Length (m)
Average 1st
peak load
(kN)
1st Peak
Load Range
(kN)
Average 1st Peak
Displacement
(mm)
B Pittsburgh 3 0.610 98 95–103 17
2 0.914 92 87–92 10
C Pittsburgh 2 0.686 59 40–77 6
Figure 7. Load-displacement curves for FGPTs, where solid
lines correspond to a 1.219 m bolt length and dotted lines
correspond to a 1.524 m bolt length
Figure 8. Head portion of fractured bolt
showing necking behavior induced by FGPT