First fracture structure characteristics of main roof plate considering elastic-plastic deformation of coal

A mechanical model for the first fracture of main roof plate structure considering the elastic-plastic deformation of coal was established in this study. According to the finite difference principle and the fracturing criterion of main bending moment,the first fracture position and order of main roof plate structure with the elastic-plastic foundation boundary as well as the influencing factors and weight relationships of the fracture morphology characteristics in the whole region of main roof were systematically calculated and studied,and the engineering significance of the mechanical model was also expounded. The following conclusions were obtained based on the above research:① When the main roof thickness h and elastic modulus E are relatively large,while the elastic coal foundation coefficient kt and the roof-hanging span of main roof are relatively small,the fracture position and order of main roof are illustrated as follows:the middle lower surface of roof in mining hanging roof area→the upper surface of roof ahead of the unplasticized elastic coal surface→the upper surface of roof along the short side of the stope ahead of the unplasticized elastic coal surface,and an O-type fracture circle will be formed in the roof on the elastic coal area. On the contrary,the fracture position and order of main roof are illustrated as follows:the upper surface of roof ahead of the plasticized coal surface→the middle lower surface of roof in mining hanging roof area→the upper surface of roof along the short side of the stope ahead of the plas-ticized coal surface,and an O-type fracture circle will be formed in the roof on the plasticized coal area. ;Finally,the “O-X” type fracture shape is formed. ② When the plasticized range of coal b0 and the plasticized degree of coal increase,the distance between the main roof fracture line ahead of the coal surface and the coal surface,and the absolute value of the main bending moment in each area of main roof will increase. That is,the roofhanging span of main roof will decrease. ③ When the plasticized range of coal b0 and the shallow plasticized coal foundation coefficient k0 are relatively large,the fracture position and order of main roof are illustrated as follows:the middle lower surface of roof in mining hanging roof area→the upper surface of roof along the long side of the stope ahead of the plasticized coal surface→the upper surface of roof along the short side of the stope ahead of the plasticized coal surface,and an O-type fracture circle will be formed in the roof on the plasticized coal area. When the values of b0 and k0 are relatively small,the fracture position and order of main roof are illustrated as follows:the upper surface of roof along the long side of the stope ahead of the elastic coal surface→the middle lower surface of roof in mining hanging roof area→the upper surface of roof along the short side of the stope ahead of the elastic coal surface,and an O-type fracture circle will be formed in the roof on the elastic coal area. Finally,the “O-X” type fracture shape is formed. ④When the ratio of k0 to kt is any constant value and the ratio of kt to h3 is also any constant value,the value and position of the main bending moment and the fracture law of main roof will remain unchanged.