6
for bolts installed at a low rotational speed of 170 rpm.
Table 1 provides a summary of the key features of all SEPTs
extracted from Figure 4.
Figure 4 clearly demonstrates the profound influence
of the rotation speed utilized during bolt installation on
the measured anchorage capacity of SEPTs. Employing
a high rotational speed during bolt installation results in
diminished anchorage capacities. A comparable trend was
previously observed by Mishra in 2015, who conducted
laboratory-based SEPTs to investigate the impact of spin
time and rotational speed on bolt performance. These find-
ings emphasize the significance of both spin time and rota-
tional speed in determining bolt capacity.
a) No. 6 bolt
Figure 5 shows post-testing images of a tested bolt that
was installed at a high rotational speed, along with snap-
shots taken inside the drilled borehole. These images reveal
that the bolt/grout interface of the No. 5 tested bolt exhib-
its signs of damage, while the grout appears to be firmly
bonded to the borehole boundaries.
The SEPTs conducted in the NIOSH Safety Research
led to the conclusion that if an optimal rotational speed
were employed during bolt installation, it is likely that
the anchorage capacity of rib bolts, as measured by SEPT,
would be equivalent to yield load of steel rebar, irrespective
of the bolt diameter.
PARTIALLY GROUTED PULL-OUT TESTS
(PGPTS)
Following the same procedure adopted for conducting
SEPTs, partially grouted pull out tests (PGPTs) for rib
bolts were tested in two mines. The rotation speed dur-
ing bolts installation was not regulated in all the PGPTs.
Unfortunately, the RPMs of the roof bolter were not
recorded in those tests. In Mine-B, two anchorage lengths
were tested (0.61 m and 0.914 m) for No. 5 bolt with bolt
length of 1.219 m. Figure 6a shows the load-displacement
curves of PGPTs in Mine-B. It shows that all PGPTs expe-
rience steel rebar yielding with stiffer loaddisplacement
Figure 5. Post-testing photographs showing No. 5 tested
bolt installed at a rotational speed of 780 rpm, along with
snapshots captured within the drilled borehole
Figure 6. Load-displacement curves of PGPTs with solid
lines denoting a 0.61 m anchorage length and dashed lines
indicating a 0.914 m anchorage length
for bolts installed at a low rotational speed of 170 rpm.
Table 1 provides a summary of the key features of all SEPTs
extracted from Figure 4.
Figure 4 clearly demonstrates the profound influence
of the rotation speed utilized during bolt installation on
the measured anchorage capacity of SEPTs. Employing
a high rotational speed during bolt installation results in
diminished anchorage capacities. A comparable trend was
previously observed by Mishra in 2015, who conducted
laboratory-based SEPTs to investigate the impact of spin
time and rotational speed on bolt performance. These find-
ings emphasize the significance of both spin time and rota-
tional speed in determining bolt capacity.
a) No. 6 bolt
Figure 5 shows post-testing images of a tested bolt that
was installed at a high rotational speed, along with snap-
shots taken inside the drilled borehole. These images reveal
that the bolt/grout interface of the No. 5 tested bolt exhib-
its signs of damage, while the grout appears to be firmly
bonded to the borehole boundaries.
The SEPTs conducted in the NIOSH Safety Research
led to the conclusion that if an optimal rotational speed
were employed during bolt installation, it is likely that
the anchorage capacity of rib bolts, as measured by SEPT,
would be equivalent to yield load of steel rebar, irrespective
of the bolt diameter.
PARTIALLY GROUTED PULL-OUT TESTS
(PGPTS)
Following the same procedure adopted for conducting
SEPTs, partially grouted pull out tests (PGPTs) for rib
bolts were tested in two mines. The rotation speed dur-
ing bolts installation was not regulated in all the PGPTs.
Unfortunately, the RPMs of the roof bolter were not
recorded in those tests. In Mine-B, two anchorage lengths
were tested (0.61 m and 0.914 m) for No. 5 bolt with bolt
length of 1.219 m. Figure 6a shows the load-displacement
curves of PGPTs in Mine-B. It shows that all PGPTs expe-
rience steel rebar yielding with stiffer loaddisplacement
Figure 5. Post-testing photographs showing No. 5 tested
bolt installed at a rotational speed of 780 rpm, along with
snapshots captured within the drilled borehole
Figure 6. Load-displacement curves of PGPTs with solid
lines denoting a 0.61 m anchorage length and dashed lines
indicating a 0.914 m anchorage length