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