Analytical solution of predicting rib spalling depth of fully-mechanized coal working face based on tri-linear strain softening model

In order to predict rib spalling depth in fully-mechanized mining faces, taking the coal wall as the research object, the coal wall is regarded as a tri-linear strain softening material. Then the direct roof and main roof are taken as macro roof, and the bearing mechanical model for the interaction between macro roof, coal seam, and support is established. Combined with the boundary conditions, the analytical solution of rib spalling depth in fully mechanized mining faces is derived in this paper. The analytical solution was used to investigate the situation of coal wall spalling in the 12401 working face of Shangwan Coal Mine, and the factors and laws influencing coal wall spalling were researched. The results show that: ① The analytical solution of rib spalling depth in the fully mechanized working face in this paper is reliable and reasonable, and can quantitatively investigate the effects of roof characteristics and support parameters. ② Increasing the initial support force can reduce rib spalling depth. Increasing the stiffness of the support can reduce rib spalling depth, however the effect is poor. The supporting strength of the support protective plate, and the rib spalling depth decreases approximately linearly. ③ With the thickness and tensile strength of the roof macroscopic increasing, the rib spalling depth increases. However its growth rate gradually slows down. The main reasons are that the periodic fracture length increases with increment of the thickness and tensile strength of the roof, which leads to increment of the angle of rotation and sinking towards the goaf. ④ The mining height has a significant effect on the rib spalling depth. The rib spalling depth linearly increases with the mining height. ⑤ With uniaxial compressive strength of coal increasing, the rib spalling depth decreases. With the interface friction coefficient between the roof and the coal increasing, the rib spalling depth decreases. ⑥ With the dynamic loading coefficient of the roof increasing, the rib spalling depth increases linearly.