9
Accumulated field data over several months revealed a
distinct pattern: broken bolts were found almost daily in
one area, followed by months of inactivity, after which sim-
ilar failures occurred elsewhere in the mine, aligned with
the direction of the cutter failure. This recurring pattern
allowed the mine operator to better anticipate future cutter
failures.
As illustrated in Figure 11, broken bolts, roof cracking,
and roof shear are mapped. The cutter, which developed
in February (dates shown in red), caused multiple bolts to
shear through February and March, followed by a quiet
period in April and May. In June, a few broken bolts, roof
cracks, and cutter activity were observed, with no activity in
July. The pattern resumed in August and September, with
roof cracking and cutter shearing.
The 7 ⁄8-inch Grade 60 bolt used for roof support in the
mine would require a differential displacement of approxi-
mately 0.0048 inches (0.12 mm) between the roof beds to
shear and break, assuming a shear length of 1 inch due to
roof separation.
3D LIDAR SCAN TO CAPTURE CUTTER
FAILURE AND ROOF FALLS
Figure 12 confirms the roof damage and orientation
observed in the mine using 3D LiDAR scanning. Scans
were taken in the same entries shown in Figure 11, validat-
ing the field observations. The point clouds were captured
using the Maptek I-Site 8200 stationary scanner at approxi-
mately 50 ft intervals. These point clouds were registered
and colored from an estimated roof line (in white), with
damage highlighted in red to indicate higher roof eleva-
tion. Both Figures 11 and 12 show that cutter failures are
oriented along the right rib of Entry 15, suggesting that
the principal horizontal stress in this area of the mine is
Figure 10. Schematic for the zig-zag pattern for the development of cutter roof failure at the
study mine, σ
v is the vertical stress, and σ
Hmax is the maximum horizontal stress.
Figure 11. Schematic illustrating the timing of roof bolt
shearing and cutter development based on accumulated field
data collected over several months
Figure 12. 3D LiDAR scans of the roof in the same entries as
Figure 11, showing cutter development, with red indicating
higher roof elevations or areas of roof damage
Accumulated field data over several months revealed a
distinct pattern: broken bolts were found almost daily in
one area, followed by months of inactivity, after which sim-
ilar failures occurred elsewhere in the mine, aligned with
the direction of the cutter failure. This recurring pattern
allowed the mine operator to better anticipate future cutter
failures.
As illustrated in Figure 11, broken bolts, roof cracking,
and roof shear are mapped. The cutter, which developed
in February (dates shown in red), caused multiple bolts to
shear through February and March, followed by a quiet
period in April and May. In June, a few broken bolts, roof
cracks, and cutter activity were observed, with no activity in
July. The pattern resumed in August and September, with
roof cracking and cutter shearing.
The 7 ⁄8-inch Grade 60 bolt used for roof support in the
mine would require a differential displacement of approxi-
mately 0.0048 inches (0.12 mm) between the roof beds to
shear and break, assuming a shear length of 1 inch due to
roof separation.
3D LIDAR SCAN TO CAPTURE CUTTER
FAILURE AND ROOF FALLS
Figure 12 confirms the roof damage and orientation
observed in the mine using 3D LiDAR scanning. Scans
were taken in the same entries shown in Figure 11, validat-
ing the field observations. The point clouds were captured
using the Maptek I-Site 8200 stationary scanner at approxi-
mately 50 ft intervals. These point clouds were registered
and colored from an estimated roof line (in white), with
damage highlighted in red to indicate higher roof eleva-
tion. Both Figures 11 and 12 show that cutter failures are
oriented along the right rib of Entry 15, suggesting that
the principal horizontal stress in this area of the mine is
Figure 10. Schematic for the zig-zag pattern for the development of cutter roof failure at the
study mine, σ
v is the vertical stress, and σ
Hmax is the maximum horizontal stress.
Figure 11. Schematic illustrating the timing of roof bolt
shearing and cutter development based on accumulated field
data collected over several months
Figure 12. 3D LiDAR scans of the roof in the same entries as
Figure 11, showing cutter development, with red indicating
higher roof elevations or areas of roof damage