3D analysis of longwall face stability in thick coal seams

Face falls remain the most difficult engineering problem in single-cut longwall mining. In this paper we investigated mining of two adjacent longwall faces using 3D nonlinear analysis, to obtain a better understanding of the stress distribution around excavations and development of failed zones. The gob loading behaviour was included by applying a variable force to the roof and floor behind the longwall face. The results show that: (1) Face failures developed in the upper portion of the face extend deeper ahead of the mined face than those in the bottom portion (2) Stress distribution and development of yielded zones ahead of the coal face vary along the panel width (3) The maximum vertical stress concentration factor (VSCF) ahead of the longwall face occurs around the middle section of the panel width (4) The middle section of a longwall face also experiences the most failed zones in the unmined coal (5) The previously mined-out face increases the VSCF and volumes of failed zones in the adjacent longwall face; however, the effect extends only a short distance along the width of the panel dose to the previously mined-out panel (6) With increasing seam height, the stiffness of the coal face is reduced and therefore the longwall face carries less vertical load, but it deforms more and the yielded zones are larger (7) With decreasing GSI of the mined seam mass, the cohesion and angle of internal friction are reduced, resulting in a lower vertical stress concentration factor and larger yielded zones spatially ahead of the face.