2
instrumented pillar, ultimately aiding in the optimization
of mine and support design.
Most underground instrumentation studies in coal
mines primarily focus on monitoring pillars and roofs, with
limited research dedicated to rib stability and rib support
design. One of the earlier studies on rib monitoring was
conducted by Smith (1992), who used a vertical rod as a
reference to measure the extent and depth of the yielding rib
zone and installed a horizontal multi-point borehole exten-
someter (MPBX) to monitor the horizontal movement at
various depths within the pillar (see Figure 1). This research
contributed to determining appropriate bolt lengths for rib
support in the studied mine. Colwell (2006) conducted
several field monitoring cases in Australian coal mines to
develop a rib support design tool known as the Analysis
and Design of Rib Support (ADRS). Heritage (2019) con-
ducted two rib monitoring studies in an Australian coal
mine, measuring rib and roof deformation along with rib
bolt loads during both development and longwall retreat
phases. This study provided insights into rib failure mech-
anisms at the monitored sites. A more recent study by
Rashed et al. (2020) conducted an extensive rib analysis
monitoring program for two geologically different sites in a
room-and-pillar mine. During pillar retreat, pillar load was
monitored, as well as roof and rib deformations and rib bolt
load. Using this data, Mohamed et al. (2020) calibrated a
numerical model and suggested design modifications to
enhance rib support based on the instrumentation data and
modeling outcomes.
Jones et al. (2014) identified stress-driven rib failure as
one of the leading cause of rib fatalities in United States
underground coal mines from 1996 to 2013. The study
indicated that rib falls due to brow formation were the pri-
mary contributors to these fatalities. Our visual
observations across various mines revealed that rib brow
formation occurs when hard coal or rock layers within the
pillar ribs overlie softer materials, such as coal. Over time,
or due to induced stresses within the coal pillar rib, these
softer layers can weaken or slough off, leading to the form-
ing of a brow (see Figure 2).
The objective of this study was to assess the potential
for brow formation in a room-and-pillar panel where the
rib was composed of a rock layer overlying a coal seam.
The rib monitoring program was designed to evaluate brow
formation during both the development and pillar retreat
loading phases.
DESCRIPTION OF THE STUDY SITE
The study mine is located in an underground coal mine
in Logan County, West Virginia. It extracts the No. 2 Gas
seam using the room-and-pillar method. Figure 3 presents
the typical geological section of the study mine. During
our tour to select the location of the instrumented site, we
observed that the mine extracts approximately 2 to 3 ft of
shale from the immediate roof, providing a mining height
of about 7 ft. This rib configuration has the potential to
form rib brows, which were observed in some locations,
especially near pillar corners (see Figure 4).
To stabilize the rock parting, rib bolting is conducted
on cycle in all entries of the study mine. A single row of 5-ft-
long angled, fully grouted rib bolts is installed in the top rock
parting whenever its thickness exceeds 2 ft. Accompanying
the installation of the rib bolts are 6-in by 6-in steel plates
and 12-in by 12-in plywood plates. The average spacing
between the installed bolts is 8 ft (see Figure 4).
Figure 2. Rib brow formation supported by timber props
Figure 1. Technique for quantifying monitoring rib profile,
after Smith (1992)
instrumented pillar, ultimately aiding in the optimization
of mine and support design.
Most underground instrumentation studies in coal
mines primarily focus on monitoring pillars and roofs, with
limited research dedicated to rib stability and rib support
design. One of the earlier studies on rib monitoring was
conducted by Smith (1992), who used a vertical rod as a
reference to measure the extent and depth of the yielding rib
zone and installed a horizontal multi-point borehole exten-
someter (MPBX) to monitor the horizontal movement at
various depths within the pillar (see Figure 1). This research
contributed to determining appropriate bolt lengths for rib
support in the studied mine. Colwell (2006) conducted
several field monitoring cases in Australian coal mines to
develop a rib support design tool known as the Analysis
and Design of Rib Support (ADRS). Heritage (2019) con-
ducted two rib monitoring studies in an Australian coal
mine, measuring rib and roof deformation along with rib
bolt loads during both development and longwall retreat
phases. This study provided insights into rib failure mech-
anisms at the monitored sites. A more recent study by
Rashed et al. (2020) conducted an extensive rib analysis
monitoring program for two geologically different sites in a
room-and-pillar mine. During pillar retreat, pillar load was
monitored, as well as roof and rib deformations and rib bolt
load. Using this data, Mohamed et al. (2020) calibrated a
numerical model and suggested design modifications to
enhance rib support based on the instrumentation data and
modeling outcomes.
Jones et al. (2014) identified stress-driven rib failure as
one of the leading cause of rib fatalities in United States
underground coal mines from 1996 to 2013. The study
indicated that rib falls due to brow formation were the pri-
mary contributors to these fatalities. Our visual
observations across various mines revealed that rib brow
formation occurs when hard coal or rock layers within the
pillar ribs overlie softer materials, such as coal. Over time,
or due to induced stresses within the coal pillar rib, these
softer layers can weaken or slough off, leading to the form-
ing of a brow (see Figure 2).
The objective of this study was to assess the potential
for brow formation in a room-and-pillar panel where the
rib was composed of a rock layer overlying a coal seam.
The rib monitoring program was designed to evaluate brow
formation during both the development and pillar retreat
loading phases.
DESCRIPTION OF THE STUDY SITE
The study mine is located in an underground coal mine
in Logan County, West Virginia. It extracts the No. 2 Gas
seam using the room-and-pillar method. Figure 3 presents
the typical geological section of the study mine. During
our tour to select the location of the instrumented site, we
observed that the mine extracts approximately 2 to 3 ft of
shale from the immediate roof, providing a mining height
of about 7 ft. This rib configuration has the potential to
form rib brows, which were observed in some locations,
especially near pillar corners (see Figure 4).
To stabilize the rock parting, rib bolting is conducted
on cycle in all entries of the study mine. A single row of 5-ft-
long angled, fully grouted rib bolts is installed in the top rock
parting whenever its thickness exceeds 2 ft. Accompanying
the installation of the rib bolts are 6-in by 6-in steel plates
and 12-in by 12-in plywood plates. The average spacing
between the installed bolts is 8 ft (see Figure 4).
Figure 2. Rib brow formation supported by timber props
Figure 1. Technique for quantifying monitoring rib profile,
after Smith (1992)