7
roofline and the pillar. Cutter failure can lead to roof falls,
with the time between the cutter failure and the roof fall
ranging from a few weeks to years. The cutter damage
appeared to zig-zag vertically in thinner beds and more
horizontally in thicker ones (see Figure 9). Simple numeri-
cal models indicate that cutter failure will stop propagating
through the roof if a gap or separation occurs between roof
beds.
Field observations revealed that bolts in the center of
the cutter (shear zone) exhibited tensile failure, with clear
cup-and-cone fractures. In contrast, bolts farther from the
center experienced shear failure. This suggests that bed sep-
aration occurs near the center of the cutter (shear zone).
In an ideal scenario with symmetric loading conditions
and a uniform, homogeneous rock mass across the entry/
heading, cutter failures would propagate at both corners
of the entry when the maximum horizontal stress is per-
pendicular to it, as shown in the schematic in Figure 10.
However, in practice, as observed at the study mine, cut-
ter failure typically propagates along one side due to asym-
metrical material properties, uneven loading conditions, or
more pronounced geological discontinuities on one side of
the heading.
The cutter failure observed at the study mine differs
from that typically seen in underground coal mines. In
coal mines, cutter failure often occurs near the rib with an
almost vertical orientation. In contrast, cutter failure in
stone mines exhibits a zig-zag pattern, see Figure 9. This
discrepancy is likely due to differences in roof strength and
lamination thickness. In coal mines, cutters usually form in
Figure 8. Shear stress distribution in the immediate roof, with values in MPa, at 0°, 30°, and 90°
orientations, the maximum horizontal stress aligned along the Y-axis
roofline and the pillar. Cutter failure can lead to roof falls,
with the time between the cutter failure and the roof fall
ranging from a few weeks to years. The cutter damage
appeared to zig-zag vertically in thinner beds and more
horizontally in thicker ones (see Figure 9). Simple numeri-
cal models indicate that cutter failure will stop propagating
through the roof if a gap or separation occurs between roof
beds.
Field observations revealed that bolts in the center of
the cutter (shear zone) exhibited tensile failure, with clear
cup-and-cone fractures. In contrast, bolts farther from the
center experienced shear failure. This suggests that bed sep-
aration occurs near the center of the cutter (shear zone).
In an ideal scenario with symmetric loading conditions
and a uniform, homogeneous rock mass across the entry/
heading, cutter failures would propagate at both corners
of the entry when the maximum horizontal stress is per-
pendicular to it, as shown in the schematic in Figure 10.
However, in practice, as observed at the study mine, cut-
ter failure typically propagates along one side due to asym-
metrical material properties, uneven loading conditions, or
more pronounced geological discontinuities on one side of
the heading.
The cutter failure observed at the study mine differs
from that typically seen in underground coal mines. In
coal mines, cutter failure often occurs near the rib with an
almost vertical orientation. In contrast, cutter failure in
stone mines exhibits a zig-zag pattern, see Figure 9. This
discrepancy is likely due to differences in roof strength and
lamination thickness. In coal mines, cutters usually form in
Figure 8. Shear stress distribution in the immediate roof, with values in MPa, at 0°, 30°, and 90°
orientations, the maximum horizontal stress aligned along the Y-axis