The influence of inter-band rock on rib spalling in longwall panel with large mining height

In order to improve rib stability, failure criteria and instability mode of a thick coal seam with inter-band rock layer are analysed in this study. A three-dimensional mechanical model is established for the rib by considering the rock layer. A safety factor is defined foy the rib, and it is observed that the safety factor exhibits a positive correlation with the thickness and strength of the inter-band rock. A calculation method for determining critical parameters of the rock layer is presented to ensure the rib stability. It is revealed that incomplete propagation of the fracture at the hard rock constitutes a fundamental prerequisite for ensuring the rib stability. The influence of the position of the inter-band rock in the coal seam on failure mechanism of the rib was thoroughly investigated by developing a series of physical models for the rib at the face area. The best position for the inter-band rock in the coal seam is at a height of 1.5 m away from the roof line, which tends to provide a good stability state for the rib. For different inter-band rock positions, two ways of controlling rib by increasing supports stiffness and flexible grouting reinforcement are proposed.