1
24-037
Examining Pull-Out Tests for Grouted Rib Bolts:
A Comprehensive Analysis
Khaled Mohamed
CDC NIOSH, Pittsburgh, PA
Yuting Xue
CDC NIOSH, Pittsburgh, PA
Dogukan Guner
Missouri University of Science and Technology,
Rolla, MO
Alper Kirmaci
Missouri University of Science and Technology,
Rolla, MO
Taghi Sherizadeh
Missouri University of Science and Technology,
Rolla, MO
ABSTRACT
Resin-grouted bolts serve as a crucial means of stabilizing
yielded coal ribs in underground coal mines. A compre-
hensive investigation into their efficacy was undertaken by
a collaborative effort between the National Institute for
Occupational Safety and Health (NIOSH) and Missouri
University of Science and Technology (MST). This study
involved pull-out tests in multiple locations, including
six coal mines and the NIOSH research mine. A total of
seventy-three (73) tests were conducted, of wide range of
anchorage lengths, ranging from a short encapsulation
length of 0.305 m to a fully grouted encapsulation length
of 1.524 m.
The test findings indicate that when short encapsula-
tion bolts are installed at high rotation speeds, their anchor-
age capacity is significantly reduced, leading to failure at
the bolt-grout interface. Conversely, when these bolts
are installed at lower rotation speeds, they exhibit greater
capacity, with failure occurring at a higher anchorage load
equivalent to the yield load of steel rebar. No matter what
the rotational speeds were used during bolt installation in
this study, the fully grouted bolts consistently experienced
failure at the ultimate load of the steel rebar. Most of the
tests carried out on partially grouted bolts with anchorage
lengths of 0.610 -0.914 m have shown behavior patterns
like the fully grouted bolts, although exhibiting reduced
stiffness. The outcomes of this research offer a profound
insight into the ways in which resin-grouted bolts enhance
the stability of coal mine ribs.
INTRODUCTION
Coal ribs, which are the walls of coal pillars, sometimes
intentionally supported during mining operations to main-
tain their structural integrity. Due to the flexibility, effec-
tiveness and relatively straightforward installation process,
rib bolting systems have been widely used in underground
coal mines. The installation of grouted bolts involves
inserting resin cartridge and bolt into a drilled borehole
and driving the bolt to break and mix the resin to form
a mechanical interlock between the bolt and surrounding
coal mass. When coal ribs start to deform and dilate, load
is generated in the bolt to reinforce the ribs. However, the
rib bolting system is complex because it involves various
components, namely bolt, grout and the surrounding coal
mass, and their interactions. The properties of these com-
ponents and their interaction potentially affect the over-
all performance of the resin-grouted rib bolts. Due to the
complexity, many different methods have been employed
to investigate the bolting behaviors through laboratory and
field testing, theoretical analysis, and numerical simulation.
The occurrence of rib falls presents severe safety risks,
encompassing injuries, fatalities, and equipment damage.
24-037
Examining Pull-Out Tests for Grouted Rib Bolts:
A Comprehensive Analysis
Khaled Mohamed
CDC NIOSH, Pittsburgh, PA
Yuting Xue
CDC NIOSH, Pittsburgh, PA
Dogukan Guner
Missouri University of Science and Technology,
Rolla, MO
Alper Kirmaci
Missouri University of Science and Technology,
Rolla, MO
Taghi Sherizadeh
Missouri University of Science and Technology,
Rolla, MO
ABSTRACT
Resin-grouted bolts serve as a crucial means of stabilizing
yielded coal ribs in underground coal mines. A compre-
hensive investigation into their efficacy was undertaken by
a collaborative effort between the National Institute for
Occupational Safety and Health (NIOSH) and Missouri
University of Science and Technology (MST). This study
involved pull-out tests in multiple locations, including
six coal mines and the NIOSH research mine. A total of
seventy-three (73) tests were conducted, of wide range of
anchorage lengths, ranging from a short encapsulation
length of 0.305 m to a fully grouted encapsulation length
of 1.524 m.
The test findings indicate that when short encapsula-
tion bolts are installed at high rotation speeds, their anchor-
age capacity is significantly reduced, leading to failure at
the bolt-grout interface. Conversely, when these bolts
are installed at lower rotation speeds, they exhibit greater
capacity, with failure occurring at a higher anchorage load
equivalent to the yield load of steel rebar. No matter what
the rotational speeds were used during bolt installation in
this study, the fully grouted bolts consistently experienced
failure at the ultimate load of the steel rebar. Most of the
tests carried out on partially grouted bolts with anchorage
lengths of 0.610 -0.914 m have shown behavior patterns
like the fully grouted bolts, although exhibiting reduced
stiffness. The outcomes of this research offer a profound
insight into the ways in which resin-grouted bolts enhance
the stability of coal mine ribs.
INTRODUCTION
Coal ribs, which are the walls of coal pillars, sometimes
intentionally supported during mining operations to main-
tain their structural integrity. Due to the flexibility, effec-
tiveness and relatively straightforward installation process,
rib bolting systems have been widely used in underground
coal mines. The installation of grouted bolts involves
inserting resin cartridge and bolt into a drilled borehole
and driving the bolt to break and mix the resin to form
a mechanical interlock between the bolt and surrounding
coal mass. When coal ribs start to deform and dilate, load
is generated in the bolt to reinforce the ribs. However, the
rib bolting system is complex because it involves various
components, namely bolt, grout and the surrounding coal
mass, and their interactions. The properties of these com-
ponents and their interaction potentially affect the over-
all performance of the resin-grouted rib bolts. Due to the
complexity, many different methods have been employed
to investigate the bolting behaviors through laboratory and
field testing, theoretical analysis, and numerical simulation.
The occurrence of rib falls presents severe safety risks,
encompassing injuries, fatalities, and equipment damage.