Numerical simulation of hard top-coal's pulsed caving in fully mechanized caving face

In order to improve the top-coal recovery in fully mechanized longwall face, the hard top-coal caving was simulated through particle flow program in three dimensions. According to the pressing cracking test of hard coal, the top-coal's fragmentation size and spatial distribution were simulated. Considering the condition of top-coal caving path, the shield beam angle, the friction coefficient between the top-coal and the shield beam were simulated also. On the basis of the 4 factors above, 3 levels of each factor were considered, so the orthogonal numerical test was carried out. Based on the evaluation index, the volume of caved top-coal, the influence of the above 4 factors on the top-coal recovery was studied through the range method. According to the kinetic energy obtained from the numerical calculation, the pulsed caving, which was affected by the appearance and disappearance of the arch, was revealed. The results showed that the size and spatial position of top-coal block is the determinants of the recovery ratio. The bigger the block, and the lower the block layer, the more obvious the arch effect. The contact force and the friction energy showed that the transient arch could become the stable arch which induced the ending of top-coal caving.