Research on the spontaneous combustion of the goaf at different advancing distances based on the dynamic evolution of porosity

Spontaneous combustion of residual coal in the goaf is one of the main disasters in coal mines. Understanding the law of spontaneous combustion of residual coal can effectively prevent coal mine fires. This paper establishes a dynamic evolution model of overburden caving and porosity in the goaf using PFC numerical simulation software, and compares and analyzes the dynamic changes in porosity and the spontaneous combustion zone at advancing distances of 50m, 70m, and 100m. The results show that when the working face advances 100m, the porosity in the caving zone of the goaf decreases from 0-0.6 to 0.16-0.3. The range of the spontaneous combustion zone on the return air side expands from 42m-50m to 39m-61m, and on the inlet side, it expands from 0 to 22m-50m. With increased exposure time, the spontaneous combustion zone range shifts slightly forward to 32m-55m on the inlet side and 21m-49m on the return side. This study reveals the dynamic evolution law of the spontaneous combustion zone in the goaf under the influence of different advancing distances and exposure times, which can assist in preventing goaf fires.