The breaking characteristics of thick-hard roof and determination of support capacity in fully mechanized caving face

It is difficult to determine the first roof weighting interval of hard roof on fully mechanized caving face.Based on the working face 8301 of Dongzhouyao coal mine, a model of two edges fixed in thick and hard roof was established by using energy method.According to the model, the horizontal stress distribution in the main roof and the analytic formula for the first roof weighting interval of the main roof were obtained.The characteristics of roof breaking and working resistance of the support were analyzed by using numerical simulation.And the working resistance of support in different positions of the working face under different advance distance was attained based on field observation.The results showed that mine pressure behaviors were more intense under the condition of thick and hard roof, with larger the first roof weighting interval and higher working resistance of support as compared to general conditions.To be specific, the first roof weighting interval was about 58 m in working face 8301, while the periodic roof weighting length ranged from 15 to 20 m.The rated working resistance of support was 13, 000 kN, but the observed maximum working resistance was 11 000 kN, only 78.7% of the rated value.It is believed that safety and efficiency of coal mining under the condition of thick and hard roof can be achieved