Study on co-existence mechanism of tensile-shear failure of rib spalling in large mining height working face

As to the serious problem of coal rib spalling during the periodic pressure in shallow buried large mining height working face,the theoretical calculation a nd numerical simulation method are used to calculate the change of elastic strain energy density before and after the roof fracture,and quantitatively indicate the energy source of coal body failure of the large mining height during the peridic pressure period.The rib spalling mechanism of large mining height is described,the cohesion w eakening and friction strengthting( CWFS) constitutive model is realized,and the rib spalling mechanism is verified.The brittleness coefficient in the CWFS model is intro duced into the rib spalling formula,and the modified coal body destruction formula is obtained.The results show that the large mining height mining causes the change 0 f the stress state in the coal body,so that the coal body is in a low confining pressure or no confining pressure state.The coal body cohesion strength component and th e shear strength component are not simultaneously activated. Rather,the cohesive force of the coal body decreases with the increase of the plastic strain,and the friction strength increases with the increase of the plastic strain,which leads to the tensile failure of the coal body in the large mining height working face,and the shear failure a Iso occurs within the coal body.Thus,the phenomenon of tensile-shear coexist.