Study on the Mechanism of a Hanging Roof at a Difficult Caving End in a Fully-Mechanized Top Coal Caving Face

During the mining process of fully-mechanized caving faces, the roof of the roadway behind the working face easily forms an arched-shape hanging roof structure with the working face pushed forward, which results in potential hazards such as gas accumulation and large-scale roof collapse. Based on the actual situation of a hanging roof at a difficult caving end in fully-mechanized top coal caving faces, through borehole exploration, surrounding rock displacement observation, bolt stress monitoring, theoretical formula calculation, and numerical simulation methods, the structure characteristics of the hanging roof at the end of the fully-mechanized caving face are studied. The ultimate failure depth and ultimate break distance of the hanging roof structure at the end of the working face are obtained, and its formation mechanism is analyzed. It is concluded that the hanging structure is formed by the following reasons: the lithology of sandy mudstone and fine sandstone above the top coal of the roadway is strong; the hanging roof structure is less affected by working-face mining; there is a result of insufficient rotary pressure of the upper mudstone while working together with the protective coal pillar and end support the caving step distance of the curved hanging roof structure is 10~13.55 m