Impact of Discrete Fracture Characteristics on Longwall Top Coal Stability

impact the top coal stability in the Longwall Top Coal Caving method
(LTCC) both ahead of shield support (top coal fall) and behind shield
support (top coal caving). The top coal stability in such conditions is
not well understood in the literature and has been studied from either
fall or caving behaviour. In this paper, a discontinuum-based
numerical program is used to study longwall top coal stability when
discrete fractures exist in coal seam and vary in characteristics (i.e.,
orientation, density, stiffness, strength, and intersecting fractures).
The study demonstrates that the existence of discrete fractures
decreases the top coal stability ahead of shield support, particularly
in initial face extraction. The parametric study finds that when the
fracture orientation makes an angle of 90 degrees to the positive xaxis, it has the least impact on top coal fall. When the fractures plunge
into the mined-out area, they facilitate top coal caving and vice versa
when they plunge into the unmined area. The study reveals that the
fracture density is directly proportional to top coal fall and top coal
caving. Meanwhile, the fracture stiffness and strength are inversely
proportional to both top coal fall and caving. The study also
demonstrates the important role of coal seam characteristics
(strength, elastic modulus, and depth) in top coal fall. The findings
from this paper can assist engineers in improving panel geometry
design and roof control for efficient underground mining when
discrete fractures exist and vary in a coal seam.