5
that in Mine-A, the steel rebar yielded in all the SEPTs for
No. 6 bolts, except for one test. Also, Figure 2e shows that
some of SEPTs encountered yielding of steel rebars and
many of the tests achieved loads of 75% of the yield load.
Figure 2f illustrates that in Mine-F, the peak loads of the
SEPTs reached 83% of the yield load, with one of the tests
intentionally terminated before reaching the point of bolt
yielding.
Could the larger bolt diameter tested in Mine-A be
a contributing factor behind achieving the yield load in
SEPTs, as illustrated in Figure 2b? Could the rotational
speed employed during bolt installation have an impact on
achieving the yield load in some of the SEPTs? To address
the preceding questions, more controllable SEPTs were
carried out in the NIOSH Safety Research Mine. These
experiments included the evaluation of two bolt sizes, No.
5 and No. 6. Additionally, two different levels of rotation
speeds were used for bolt installation: 170 rpm and 780
rpm. Figure 3 displays images illustrating the process of cre-
ating a horizontal hole in an almost vertical coal pillar rib,
along with a photo of the bolts successfully installed within
the coal seam.
Figure 4 presents load-displacement curves resulting
from all SEPTs conducted at the NIOSH Safety Research
mine. The solid lines represent the load-displacement curves
of bolts installed at a high rotational speed of 780 rpm,
while the dashed lines show the load-displacement curves
Figure 3. SEPTs preparation carried out at the
NIOSH Safety Research Mine
Figure 4. Load-displacement curves for SEPTs conducted
in NIOSH Safety Research Mine – Solid curves represent
bolts installed at high rotation speed of 780 rpm and Dotted
curves represent bolts installed at low rotation speed of
170 rpm
that in Mine-A, the steel rebar yielded in all the SEPTs for
No. 6 bolts, except for one test. Also, Figure 2e shows that
some of SEPTs encountered yielding of steel rebars and
many of the tests achieved loads of 75% of the yield load.
Figure 2f illustrates that in Mine-F, the peak loads of the
SEPTs reached 83% of the yield load, with one of the tests
intentionally terminated before reaching the point of bolt
yielding.
Could the larger bolt diameter tested in Mine-A be
a contributing factor behind achieving the yield load in
SEPTs, as illustrated in Figure 2b? Could the rotational
speed employed during bolt installation have an impact on
achieving the yield load in some of the SEPTs? To address
the preceding questions, more controllable SEPTs were
carried out in the NIOSH Safety Research Mine. These
experiments included the evaluation of two bolt sizes, No.
5 and No. 6. Additionally, two different levels of rotation
speeds were used for bolt installation: 170 rpm and 780
rpm. Figure 3 displays images illustrating the process of cre-
ating a horizontal hole in an almost vertical coal pillar rib,
along with a photo of the bolts successfully installed within
the coal seam.
Figure 4 presents load-displacement curves resulting
from all SEPTs conducted at the NIOSH Safety Research
mine. The solid lines represent the load-displacement curves
of bolts installed at a high rotational speed of 780 rpm,
while the dashed lines show the load-displacement curves
Figure 3. SEPTs preparation carried out at the
NIOSH Safety Research Mine
Figure 4. Load-displacement curves for SEPTs conducted
in NIOSH Safety Research Mine – Solid curves represent
bolts installed at high rotation speed of 780 rpm and Dotted
curves represent bolts installed at low rotation speed of
170 rpm