4
Therefore, there is no multiple-seam interaction expected
at the study panel.
Table 1 lists the immediate roof lithology within the
bolting horizon, determined by scoping holes up to 8.5 ft
into the roof near the instrumented pillar. It shows that the
immediate roof at the study site consists primarily of shale,
with coal and sandstone streaks
The lithology of the rib in instrumented pillar P3,
observed at the study site, is illustrated in Figure 7. The
rib height varies between 6.2 ft and 7 ft and consists of
a 3.7-ft to 4-ft coal seam, situated between a rock part-
ing (2 to 2.5 ft thick) and a bottom rock parting (0.5 ft
thick). The angle between the face cleat and the orientation
of entry No. 4 at the instrumented pillar was measured to
be 80 degrees. The ribs of pillar P3 are supported by a row
of fully grouted, 5-ft-long No. 6 Grade 60 bolts, spaced
approximately 6 ft apart (see Figure 7). These rib bolts are
installed in the rock parting, near the roofline, at an angle
of 20 to 30 degrees. Their primary function is to anchor
the rock parting to the immediate roof, avoiding rib brow
formation.
The uniaxial compressive strengths of the rock parting
and coal seam were estimated through indirect measure-
ments using Schmidt hammer rebound tests on the rib
of an instrumented pillar. The average Schmidt hammer
rebound numbers (N) recorded were 38 for the rock part-
ing and 35 for the coal seam. These rebound values were
then applied to Equation (1) (Saptono et al., 2013) for the
rock parting and Equation (2) (Rashed et al., 2018) for the
coal seam to estimate the uniaxial compressive strengths,
respectively. Based on these calculations, the uniaxial com-
pressive strengths were determined to be 5,556 psi for the
rock parting and 3,747 psi for the coal seam.
UCS for shale (psi) =44.66*N1.327 (1)
UCS for coal (psi) =215.7*N-3,779 (2)
DESCRIPTION OF THE INSTRUMENT
LAYOUT
The instruments in pillar P3 were installed while the con-
tinuous miner was advancing one-break inby the instru-
mented pillar. Figure 8 illustrates a scaled layout of the
instrumented pillar P3, showing the positions of roof
extensometers (RX), load cells (LC), borehole pressure cells
(BPC), and multi-point borehole extensometers (MPBX).
Roof extensometers RX1 and RX2 were installed to
monitor roof displacements in the middle of entry No. 4
and cross-cut No. 24, respectively. The anchor point for
each roof extensometer was positioned at a depth of 15 ft
into the roof, which is approximately equal to the width of
the entry at the study site. This depth was selected to ensure
that the anchors experience minimal induced stress from
both the entry and the cross-cut.
Load cells (LC) were mounted on 5-ft-long, No. 6,
Grade 60 rib bolts with a grout length of 34 in. to measure
the induced loads in the rib bolts at both the entry and the
cross-cut. LC-1, LC-2, and LC-3 were installed in the entry
side (entry No. 4) of the instrumented pillar, while LC-4,
Table 1. Roof lithology scoped in entry no. 4
Rock layer Thickness, ft
Shale (top) 1.9
Shale with sandstone streak 0.1
Shale/dark coal streak 1.4
Shale with sandstone streak 0.2
Shale 4.6
Crack zone/sandstone 0.1
Shale (bottom) 0.2
Figure 7. Rib lithology as observed at the instrumented pillar
(P3)
Figure 8. Layout of instrument in Pillar (P3)
Therefore, there is no multiple-seam interaction expected
at the study panel.
Table 1 lists the immediate roof lithology within the
bolting horizon, determined by scoping holes up to 8.5 ft
into the roof near the instrumented pillar. It shows that the
immediate roof at the study site consists primarily of shale,
with coal and sandstone streaks
The lithology of the rib in instrumented pillar P3,
observed at the study site, is illustrated in Figure 7. The
rib height varies between 6.2 ft and 7 ft and consists of
a 3.7-ft to 4-ft coal seam, situated between a rock part-
ing (2 to 2.5 ft thick) and a bottom rock parting (0.5 ft
thick). The angle between the face cleat and the orientation
of entry No. 4 at the instrumented pillar was measured to
be 80 degrees. The ribs of pillar P3 are supported by a row
of fully grouted, 5-ft-long No. 6 Grade 60 bolts, spaced
approximately 6 ft apart (see Figure 7). These rib bolts are
installed in the rock parting, near the roofline, at an angle
of 20 to 30 degrees. Their primary function is to anchor
the rock parting to the immediate roof, avoiding rib brow
formation.
The uniaxial compressive strengths of the rock parting
and coal seam were estimated through indirect measure-
ments using Schmidt hammer rebound tests on the rib
of an instrumented pillar. The average Schmidt hammer
rebound numbers (N) recorded were 38 for the rock part-
ing and 35 for the coal seam. These rebound values were
then applied to Equation (1) (Saptono et al., 2013) for the
rock parting and Equation (2) (Rashed et al., 2018) for the
coal seam to estimate the uniaxial compressive strengths,
respectively. Based on these calculations, the uniaxial com-
pressive strengths were determined to be 5,556 psi for the
rock parting and 3,747 psi for the coal seam.
UCS for shale (psi) =44.66*N1.327 (1)
UCS for coal (psi) =215.7*N-3,779 (2)
DESCRIPTION OF THE INSTRUMENT
LAYOUT
The instruments in pillar P3 were installed while the con-
tinuous miner was advancing one-break inby the instru-
mented pillar. Figure 8 illustrates a scaled layout of the
instrumented pillar P3, showing the positions of roof
extensometers (RX), load cells (LC), borehole pressure cells
(BPC), and multi-point borehole extensometers (MPBX).
Roof extensometers RX1 and RX2 were installed to
monitor roof displacements in the middle of entry No. 4
and cross-cut No. 24, respectively. The anchor point for
each roof extensometer was positioned at a depth of 15 ft
into the roof, which is approximately equal to the width of
the entry at the study site. This depth was selected to ensure
that the anchors experience minimal induced stress from
both the entry and the cross-cut.
Load cells (LC) were mounted on 5-ft-long, No. 6,
Grade 60 rib bolts with a grout length of 34 in. to measure
the induced loads in the rib bolts at both the entry and the
cross-cut. LC-1, LC-2, and LC-3 were installed in the entry
side (entry No. 4) of the instrumented pillar, while LC-4,
Table 1. Roof lithology scoped in entry no. 4
Rock layer Thickness, ft
Shale (top) 1.9
Shale with sandstone streak 0.1
Shale/dark coal streak 1.4
Shale with sandstone streak 0.2
Shale 4.6
Crack zone/sandstone 0.1
Shale (bottom) 0.2
Figure 7. Rib lithology as observed at the instrumented pillar
(P3)
Figure 8. Layout of instrument in Pillar (P3)