Zoning characteristics and critical stress conditions of crack propagation in the longwall panel floor
In order to analyze the mechanism of crack propagation in the longwall panel floor,the mechanical model of crack propagation in the longwall panel floor was established,and the critical stress conditions for fracture propagation in different areas of the longwall panel floor were derived,and the research results were verified by numerical simulation and field monito-ring.The results show that the floor failure has undergone five processes:shear slip,Ⅰ/Ⅱfracture propagation,flexural fracture propagation,macroscopic shear failure and unloading tensile failure.When pure type Ⅰ fracture and pure type Ⅱ fracture occur in the floor,the critical stress increases with the increase of the stress ratio and the friction coefficient of the fracture surface,and the critical stress in the floor when the pure type Ⅱ fracture occurs is al-ways less than that of the pure type Ⅰ fracture;The critical stress decreases with the increase of the stress ratio when the bending crack propagation occurs in the floor,and increases with the increase of the stress ratio when shear failure occurs;When the unloading tensile failure occurs in the floor,the critical stress is mainly related to the unloading amount and the stress concentration coefficient at the defect,and the stress concentration coefficient at the defect mainly affects the critical unloading amount,and the larger the unloading amount,the smaller the critical stress.
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