Distribution and Evolution Law of Void Fraction in the Goaf of Longwall Mining in a Coal Mine: Calculation Method and Numerical Simulation Verification

Many voids are produced in the mining process of ore-bearing strata. To explore the development law of voids after mining coal-bearing strata, a theoretical model was established to derive the overall distribution and shape of voids in the goaf. The above theory was verified using the numerical calculation method. The turning point of the void change was found. The research results show that the void in the goaf was widely distributed around the stope, and the overall void ratio was affected by the mining conditions, such as the mining height and face length. While advancing the working face, the dynamic development of the void first increased and then decreased. At first, the distribution of the void ratio in the goaf was between 0.293 and 0.889 under specific geological conditions, and then, with the advancement of the working face, a large void ratio was reserved at 0 similar to 40 m behind the working face. When the working face was advanced to the first roof collapse length, the void fractures continued to decline. Using the above voids, the backfilling of solid mine waste can be effectively realized, and the ecological environment can be protected.