A new method for improving coal wall stability in longwall mining by considering support stiffness

To propose a support stiffness based method for improving the stability of coal wall, static stiffness of the support and fracture development of the coal wall are monitored during retraction period of a panel in the second coal mine of Zhaogu coalfield. It is revealed that the range of support stiffness falls between 50 and 450 MN/m. In face length direction, support stiffness is characterized by three zones. It is small in the middle section while large magnitude is observed at two end areas. Fracture development of the coal wall is detected by geological radar, which reveal that fracture development is high in the middle section, and a decreasing trend is experienced from the middle to side areas. Such results imply face stability is strongly influenced by support stiffness. Based on such understanding, mechanical model for supporting system of the longwall face is established by considering the stiffness. The results demonstrate that roof pressure transferred onto the coal wall is negatively related to support stiffness. Then, in situ monitored relationship between support stiffness and fracture development of the coal wall is reasonably explained. Moreover, numerical modeling is carried out to validate the influence of support stiffness on face stability, and the results show the minimum support stiffness is proposed to be 100 MN/m for the target panel. The study provides a new method for selecting support stiffness in longwall panel with similar geological conditions.