2
The effectiveness of the rib bolting systems mainly depends
on the rib support design, which can be affected by the
local geological condition, the type and size of coal ribs,
and the load and stress on the ribs. Inadequate support
design could result in insufficient reinforcement and sub-
sequent rib instabilities. The rib bolting design in U.S.
underground coal mines currently relies on a trial-and-
error approach. Researchers from the National Institute for
Occupational Safety and Health (NIOSH) have been work-
ing on the development of -an engineering-based approach
for coal rib stability analysis and bolting design (Dolinar, et
al., 1991, Mohamed, et al., 2019, Mohamed, et al., 2023).
Pull-out test is a conventional method to investigate the
load transfer mechanism and anchoring ability of bolts,
providing crucial information for engineering-based rib
support design. It involves the gradual application of axial
load using a hydraulic jack to measure the force required
for the bolt to be pulled out and provides valuable informa-
tion about the anchorage capability of the bolts for bolting
design. Pull-out tests can be conducted either in laboratory
or on field. Figure 1 shows a schematic drawing of the com-
ponents of the standard pull gear.
Laboratory tests are often favored over field tests due to
their cost-effectiveness and ease of control (Blanco Martín
et al., 2011 Ma et al., 2017 Ma et al., 2013 Bastami et al.,
2017 Chen et al., 2018 Bartels and Pappas 1985). These
laboratory experiments provide several advantages, enabling
the examination of various factors affecting bolt perfor-
mance. These factors encompass grout properties (Kilic
et al., 2002) bolt surface configurations (Aziz et al., 2006
and Tao et al., 2017) bolt diameters (Rao Karanam and
Dasyapu, 2005) host rock properties (Bartels and Pappas,
1985) and confining pressure (Moosavi et al., 2001).
It is important to recognize that the bond characteris-
tics observed in laboratory tests may not accurately repre-
sent the conditions of bolts in the field. These- laboratory
tests do- not account for various- factors, such as the pres-
ence of resin cartridge film, and machinery effects, all of
which have the potential to impact bolt performance. In a
comprehensive study conducted by Cincilla in 1986, over
1,000 pull-out tests were carried out on roof bolts across
11 underground coal mines throughout the United States.
These tests encompassed various anchorage lengths of
0.305, 0.457, 0.610, and 1.219 m. The findings revealed
a repeated trend: in most of the roof bolt tests, the behav-
ior of the steel rebar became the dominant factor in the
bolt’s response to axial loading conditions imposed dur-
ing the pull-out test, typically once the resin grout length
exceeded approximately 0.610 m. To further investigate
the anchorage failure of roof bolts, Mark et al. (2000) con-
ducted Short Encapsulation Pull Tests (SEPT) in the roofs
of underground coal mines. These tests grouted only the
top 0.305 m of the bolt so that the bolts would not reach
yielding during the tests. Subsequently, Chugh et al., 2016
carried out SEPTs to establish a comprehensive database
for mine roofs in the Illinois coal basin. Their dataset com-
prised data from over 200 tests conducted in 20 mines across
Illinois, Indiana, and Western Kentucky, encompassing a
Figure 1. Pull-out test gear components
The effectiveness of the rib bolting systems mainly depends
on the rib support design, which can be affected by the
local geological condition, the type and size of coal ribs,
and the load and stress on the ribs. Inadequate support
design could result in insufficient reinforcement and sub-
sequent rib instabilities. The rib bolting design in U.S.
underground coal mines currently relies on a trial-and-
error approach. Researchers from the National Institute for
Occupational Safety and Health (NIOSH) have been work-
ing on the development of -an engineering-based approach
for coal rib stability analysis and bolting design (Dolinar, et
al., 1991, Mohamed, et al., 2019, Mohamed, et al., 2023).
Pull-out test is a conventional method to investigate the
load transfer mechanism and anchoring ability of bolts,
providing crucial information for engineering-based rib
support design. It involves the gradual application of axial
load using a hydraulic jack to measure the force required
for the bolt to be pulled out and provides valuable informa-
tion about the anchorage capability of the bolts for bolting
design. Pull-out tests can be conducted either in laboratory
or on field. Figure 1 shows a schematic drawing of the com-
ponents of the standard pull gear.
Laboratory tests are often favored over field tests due to
their cost-effectiveness and ease of control (Blanco Martín
et al., 2011 Ma et al., 2017 Ma et al., 2013 Bastami et al.,
2017 Chen et al., 2018 Bartels and Pappas 1985). These
laboratory experiments provide several advantages, enabling
the examination of various factors affecting bolt perfor-
mance. These factors encompass grout properties (Kilic
et al., 2002) bolt surface configurations (Aziz et al., 2006
and Tao et al., 2017) bolt diameters (Rao Karanam and
Dasyapu, 2005) host rock properties (Bartels and Pappas,
1985) and confining pressure (Moosavi et al., 2001).
It is important to recognize that the bond characteris-
tics observed in laboratory tests may not accurately repre-
sent the conditions of bolts in the field. These- laboratory
tests do- not account for various- factors, such as the pres-
ence of resin cartridge film, and machinery effects, all of
which have the potential to impact bolt performance. In a
comprehensive study conducted by Cincilla in 1986, over
1,000 pull-out tests were carried out on roof bolts across
11 underground coal mines throughout the United States.
These tests encompassed various anchorage lengths of
0.305, 0.457, 0.610, and 1.219 m. The findings revealed
a repeated trend: in most of the roof bolt tests, the behav-
ior of the steel rebar became the dominant factor in the
bolt’s response to axial loading conditions imposed dur-
ing the pull-out test, typically once the resin grout length
exceeded approximately 0.610 m. To further investigate
the anchorage failure of roof bolts, Mark et al. (2000) con-
ducted Short Encapsulation Pull Tests (SEPT) in the roofs
of underground coal mines. These tests grouted only the
top 0.305 m of the bolt so that the bolts would not reach
yielding during the tests. Subsequently, Chugh et al., 2016
carried out SEPTs to establish a comprehensive database
for mine roofs in the Illinois coal basin. Their dataset com-
prised data from over 200 tests conducted in 20 mines across
Illinois, Indiana, and Western Kentucky, encompassing a
Figure 1. Pull-out test gear components