6
CUTTER FAILURE INITIATION AND
DEVELOPMENT
Cutter roof failure is primarily attributed to shear stress at
the entry corner exceeding the shear strength of the rock.
Figure 8 illustrates the shear stress distribution in the imme-
diate roof above Entry 1 at 0°, 30°, and 90° orientations
from FLAC3D models. Note that Entry 2 and the Crosscut
have not been mined yet.
At 0° orientation, the maximum shear stress is concen-
trated at the face, indicating that failure would likely occur
there. In contrast, at 90° orientation, shear stress peaks at
the sides and is lowest at the face, suggesting that failure
is expected to happen at the sides. The shear stress at 90°
orientation is significantly higher than at 0°. At a 30° orien-
tation, one corner experiences a higher shear stress concen-
tration compared to the other corner, indicating that failure
would initiate at that corner and propagate along both the
face and the side near the stressed corner.
Roof cutter failure is a progressive phenomenon driven
by shear failure, which initiates at the intersection of the
Figure 6. Variation of percent roof failure with maximum
horizontal stress orientation for a) Entry 1 and b) Crosscut
based on FLAC3D elastic models. The caprock thickness is
2 ft (0.61 m)
Figure 7. Distribution of maximum principal stress
(s1) in the roof of Entry 1: a) when Entry 1 is oriented
perpendicular to the maximum horizontal stress and
b) when Entry 1 is oriented parallel to the maximum
horizontal stress. Stress values are in MPa. Note that
Entry 2 and the Crosscut have not been mined yet
CUTTER FAILURE INITIATION AND
DEVELOPMENT
Cutter roof failure is primarily attributed to shear stress at
the entry corner exceeding the shear strength of the rock.
Figure 8 illustrates the shear stress distribution in the imme-
diate roof above Entry 1 at 0°, 30°, and 90° orientations
from FLAC3D models. Note that Entry 2 and the Crosscut
have not been mined yet.
At 0° orientation, the maximum shear stress is concen-
trated at the face, indicating that failure would likely occur
there. In contrast, at 90° orientation, shear stress peaks at
the sides and is lowest at the face, suggesting that failure
is expected to happen at the sides. The shear stress at 90°
orientation is significantly higher than at 0°. At a 30° orien-
tation, one corner experiences a higher shear stress concen-
tration compared to the other corner, indicating that failure
would initiate at that corner and propagate along both the
face and the side near the stressed corner.
Roof cutter failure is a progressive phenomenon driven
by shear failure, which initiates at the intersection of the
Figure 6. Variation of percent roof failure with maximum
horizontal stress orientation for a) Entry 1 and b) Crosscut
based on FLAC3D elastic models. The caprock thickness is
2 ft (0.61 m)
Figure 7. Distribution of maximum principal stress
(s1) in the roof of Entry 1: a) when Entry 1 is oriented
perpendicular to the maximum horizontal stress and
b) when Entry 1 is oriented parallel to the maximum
horizontal stress. Stress values are in MPa. Note that
Entry 2 and the Crosscut have not been mined yet