3
broad range of overburden depths, bolt lengths, and bolt
diameters. The SEPTs conducted by Aziz et al. (2016) fur-
ther confirmed that an encapsulation length of 0.305 m is
appropriate for pull-out tests aimed at investigating roof
bolt anchorage failure. Extending the encapsulation length
beyond this point was found to potentially induce bolt
yielding.
However, it is important to highlight that there is a
significant lack of pull-out tests performed on the rib bolts,
indicating the need for additional research in this specific
area. This paper represents ongoing research, jointly under-
taken by the National Institute for Occupational Safety and
Health (NIOSH) and Missouri University of Science and
Technology (MST). The objective of this study is to con-
duct a comprehensive investigation of the effectiveness of
rib bolting in various coal seams within the Eastern mines
of the United States. This will be accomplished by perform-
ing a series of pull-out tests in those mines in addition to
the NIOSH Safety Research mine.
IN-SITU PULL OUT TESTS FOR RESIN-
GROUTED RIB
A total of 73 pull-out tests were carried out across six dif-
ferent coal mines and at the NIOSH Safety Research
mine. The rib bolts were tested in five different coal seams:
Pittsburgh seam, No 2 Gas seam, Kellioka seam, Jawbone
seam, and Pocahontas No. 3 seam. No. 5 bolts, which has a
diameter of 15.875 mm, were the dominantly tested bolts
in this study although a limited number of No. 6 bolts with
a diameter of 19.05 mm were also tested. All the tested
bolts were grade 60 with a tensile strength of 414 MPa.
The yield loads for No. 5 and No. 6 bolts are 82 kN and
118 kN, respectively. Most of the tested bolts were 1.219 m
long, although some were 1.524 m in length. All the tested
bolts were installed into holes with a 25.4 mm diameter,
while the resin cartridge had a diameter of 23 mm.
Three different anchorage types of rib bolts were exam-
ined in this study: (1) Fifty-one (51) pull-out tests were
conducted on Short Encapsulation (SEPT) bolts, each hav-
ing an anchorage length of 0.305 m, (2) Fifteen (15) pull-
out tests were conducted on fully grouted bolts (FGPT),
and (3) Seven (7) pull-out tests were conducted on partially
grouted bolts (PGPT), with anchorage lengths ranges from
0.610 m to 0.914 m.
All the rib bolts were installed within the coal seams.
Most of the bolts were installed horizontally, although
there were a few exceptions where the installation devi-
ated from the horizontal orientation. Typically, we did not
select the resin type for pull-out tests. Instead, we used the
resin cartridge employed by the mine for rib bolting and
follow their method of bolt installation. The spin time for
all tested bolts was approximately 4–10 seconds, with a
hold time of around 60 seconds. A minimum of 2 hours
elapsed between bolt installation and testing. It is impor-
tant to highlight that different roof bolters and operators
participated in the installation of rib bolts in this study.
The speed of bolt installation was generally unregulated,
except when tests were performed in the NIOSH Research
Mine. The tested bolts were subjected to a minimum axial
displacement at the bolt head of 20 mm. In the process of
conducting pullout tests on rib bolts, our primary goal was
to prevent exceeding the fracture load of the steel rebar,
except in few cases where the intention was to apply force
until the bolt fractured, while adhering to all essential safety
precautions.
SHORT ENCAPSULATION PULL-OUT
TESTS (SEPTS)
To assess the anchorage capacity of grout while avoiding the
yielding of steel rebar, the anchorage length for all SEPTs
was set to 0.305 m, as established in previous research stud-
ies (Mark et al., 2000 Chugh et al., 2016
Aziz et al., 2016). Figure 2 displays the load-displace-
ment curves obtained from the SEPTs conducted in six dif-
ferent mines. The y-axis represents the recorded load in kN,
while the x-axis represents the measured head displacement
in mm. The red line indicates the yield load of the exam-
ined bolts in kN. It’s worth mentioning that the SEPTs for
rib bolts No. 5 and No. 6 in Mine-A, were installed on dif-
ferent days by different operators. Additionally, the tests in
MineE intentionally terminated before reaching bolt yield-
ing, because of inadequate safety precautions in the event
of bolt failures.
It is apparent from Figure 2 that there is no unique
load-displacement pattern that can be extracted from the
conducted SEPTs. These tests exhibited a range of behav-
iors, with some SEPTs demonstrating softening character-
istics, while others exhibited a consistent plastic behavior.
Table 1 provides a summary of the key features extracted
from Figure 2 for all the SEPTs. Notably, Table 1 shows a
significant variation in the measured average peak loads for
No. 5 Bolts, ranging from 26% to 88% of the yield load of
steel rebar. Conversely, No. 6 bolts exhibit consistent aver-
age peak loads, ranging between 83% and 74% of the yield
load of steel rebar.
Prior to carrying out the SEPTs, there was no expec-
tation that any of the tested bolts would yield, and that
failure would happen at the grout/bolt interface. However,
the tests revealed that in many of the performed SEPTs,
bolt failure was the result of steel yielding. Figure 2b shows
broad range of overburden depths, bolt lengths, and bolt
diameters. The SEPTs conducted by Aziz et al. (2016) fur-
ther confirmed that an encapsulation length of 0.305 m is
appropriate for pull-out tests aimed at investigating roof
bolt anchorage failure. Extending the encapsulation length
beyond this point was found to potentially induce bolt
yielding.
However, it is important to highlight that there is a
significant lack of pull-out tests performed on the rib bolts,
indicating the need for additional research in this specific
area. This paper represents ongoing research, jointly under-
taken by the National Institute for Occupational Safety and
Health (NIOSH) and Missouri University of Science and
Technology (MST). The objective of this study is to con-
duct a comprehensive investigation of the effectiveness of
rib bolting in various coal seams within the Eastern mines
of the United States. This will be accomplished by perform-
ing a series of pull-out tests in those mines in addition to
the NIOSH Safety Research mine.
IN-SITU PULL OUT TESTS FOR RESIN-
GROUTED RIB
A total of 73 pull-out tests were carried out across six dif-
ferent coal mines and at the NIOSH Safety Research
mine. The rib bolts were tested in five different coal seams:
Pittsburgh seam, No 2 Gas seam, Kellioka seam, Jawbone
seam, and Pocahontas No. 3 seam. No. 5 bolts, which has a
diameter of 15.875 mm, were the dominantly tested bolts
in this study although a limited number of No. 6 bolts with
a diameter of 19.05 mm were also tested. All the tested
bolts were grade 60 with a tensile strength of 414 MPa.
The yield loads for No. 5 and No. 6 bolts are 82 kN and
118 kN, respectively. Most of the tested bolts were 1.219 m
long, although some were 1.524 m in length. All the tested
bolts were installed into holes with a 25.4 mm diameter,
while the resin cartridge had a diameter of 23 mm.
Three different anchorage types of rib bolts were exam-
ined in this study: (1) Fifty-one (51) pull-out tests were
conducted on Short Encapsulation (SEPT) bolts, each hav-
ing an anchorage length of 0.305 m, (2) Fifteen (15) pull-
out tests were conducted on fully grouted bolts (FGPT),
and (3) Seven (7) pull-out tests were conducted on partially
grouted bolts (PGPT), with anchorage lengths ranges from
0.610 m to 0.914 m.
All the rib bolts were installed within the coal seams.
Most of the bolts were installed horizontally, although
there were a few exceptions where the installation devi-
ated from the horizontal orientation. Typically, we did not
select the resin type for pull-out tests. Instead, we used the
resin cartridge employed by the mine for rib bolting and
follow their method of bolt installation. The spin time for
all tested bolts was approximately 4–10 seconds, with a
hold time of around 60 seconds. A minimum of 2 hours
elapsed between bolt installation and testing. It is impor-
tant to highlight that different roof bolters and operators
participated in the installation of rib bolts in this study.
The speed of bolt installation was generally unregulated,
except when tests were performed in the NIOSH Research
Mine. The tested bolts were subjected to a minimum axial
displacement at the bolt head of 20 mm. In the process of
conducting pullout tests on rib bolts, our primary goal was
to prevent exceeding the fracture load of the steel rebar,
except in few cases where the intention was to apply force
until the bolt fractured, while adhering to all essential safety
precautions.
SHORT ENCAPSULATION PULL-OUT
TESTS (SEPTS)
To assess the anchorage capacity of grout while avoiding the
yielding of steel rebar, the anchorage length for all SEPTs
was set to 0.305 m, as established in previous research stud-
ies (Mark et al., 2000 Chugh et al., 2016
Aziz et al., 2016). Figure 2 displays the load-displace-
ment curves obtained from the SEPTs conducted in six dif-
ferent mines. The y-axis represents the recorded load in kN,
while the x-axis represents the measured head displacement
in mm. The red line indicates the yield load of the exam-
ined bolts in kN. It’s worth mentioning that the SEPTs for
rib bolts No. 5 and No. 6 in Mine-A, were installed on dif-
ferent days by different operators. Additionally, the tests in
MineE intentionally terminated before reaching bolt yield-
ing, because of inadequate safety precautions in the event
of bolt failures.
It is apparent from Figure 2 that there is no unique
load-displacement pattern that can be extracted from the
conducted SEPTs. These tests exhibited a range of behav-
iors, with some SEPTs demonstrating softening character-
istics, while others exhibited a consistent plastic behavior.
Table 1 provides a summary of the key features extracted
from Figure 2 for all the SEPTs. Notably, Table 1 shows a
significant variation in the measured average peak loads for
No. 5 Bolts, ranging from 26% to 88% of the yield load of
steel rebar. Conversely, No. 6 bolts exhibit consistent aver-
age peak loads, ranging between 83% and 74% of the yield
load of steel rebar.
Prior to carrying out the SEPTs, there was no expec-
tation that any of the tested bolts would yield, and that
failure would happen at the grout/bolt interface. However,
the tests revealed that in many of the performed SEPTs,
bolt failure was the result of steel yielding. Figure 2b shows