Coal wall failure mechanism of longwall working face with false dip in steep coal seam

The coal wall and floor of the longwall face in the steeply inclined coal seam are prone to damage,which se- riously affects the advance of the working face. By establishing theoretical model,bottom friction experiments,numeri- cal calculations,etc. ,the characteristics of coal seam roof breaking and caving rock sliding are studied,and the coal wall failure mechanism under different coal seam occurrence and mining conditions is revealed. The concrete measures to prevent coal wall damage and floor slip are put forward. The study shows that the caving rock from the roof of the longwall face in steeply inclined coal seams will form different degrees of filling in the goaf. From bottom to top,it forms three sections including “compact filling section”,“uneven filling section” and “non-filling section”. However, due to insufficient filling in the upper part of the working face,the dynamic pressure phenomenon is obvious,which is likely to cause serious coal wall slab and bottom plate slip phenomenon,and the working condition of the support will also become worse,which becomes the most unstable surrounding rock of the whole working face. The fragile area seriously affects the safe and efficient production of the working face,and is the key area for the surrounding rock control of the working face. The stability of the working floor is significantly affected by the stability of the coal wall. In actual production,it is found that when the coal seam occurrence and mining conditions are different,the coal wall failure generally presents three failure modes:“plastic-flow”,“extrusion-slip” and “shear-slip”. The use of a pseudo-tilt ar- rangement at the working face not only can significantly improve the stability of the coal wall and the bottom plate,but also effectively prevent the hydraulic support from falling and sliding, and can also avoid the occurrence of flying gangue at the working face. With the integration of conveyor and the “flexible reinforced coal wall”,it is possible to re- alize the safe and efficient mining of longwall working face in steep coal seam,and effectively solve a series of rock for- mation control problems faced by the mechanized mining of steep coal seam.