Longwall face stability analysis from a discontinuum-Discrete Fracture Network modelling

• Published in: Tunnelling and underground space technology Vol. 124; p. 104480
• Main Authors: Le, Tien Dung, Oh, Joung
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01.06.2022; Elsevier BV
• Subjects: Building codes; Coal; Coal face spall; DFN; Face stability; Failure rates; Fracture characteristics; Fracture strength; Fracture toughness; Geological engineering; Longwall mining; Mining engineering; Overburden; Stability analysis; Stiffness; Stress analysis; Top coal fall; UDEC; Underground construction; Underground mining; Face stability; Fracture characteristics; Coal face spall; UDEC; Top coal fall; DFN
• ISSN: 0886-7798; 1878-4364
• DOI: 10.1016/j.tust.2022.104480

[Display omitted] •Face spall interacts with top coal fall, reducing longwall safety and productivity.•Face spall and top coal fall, previously studied separately, are jointly investigated.•Coal seam fractures are stochastically modelled based on field measurements.•Face stability is dependent on fracture orientation and fracture density.•Face stability is directly proportional to fracture strength and fracture stiffness. This paper presents the longwall face stability analysis under a realistic representation of geological structures and caving behaviours within coal seam. Face spall and its accompanying top coal fall, previously studied separately from each other, are jointly investigated by using a discontinuum-based code with a built-in Discrete Fracture Network (DFN) generator. The study provides further evidence to demonstrate that longwall mining forms increasing relief zones of vertical and horizontal stresses in vertically and horizontally elliptical shapes, respectively. Well ahead of face line intact blocks and fractures predominantly fail in shear while near face line fractures predominantly fail in tension. Both coal face spall and top coal fall ahead of shied support are found to occur in gravity-induced caving mode, and the spall is most severe at the top portion of face line. The study reveals that a longwall face is least stable when its fractures plunge into mined-out area and make an angle of 45 degrees with the overburden loading direction. The face is more stable when the fractures plunge into unmined area rather than when plunge into mined-out area. The stability of longwall face is found to be directly proportional to fracture strength. An increase in fracture stiffness decreases coal face spall and top coal fall rates but at the same time it increases fracture failure rate to some extent. The findings from this study can assist engineers in better identifying longwall face instability risks and accordingly improving face control for safe and productive underground longwall mining.