Space-time porosity distribution on overlying strata above a shallow seam

Flow field maldistribution often leads to problems, such as the easy enrichment of stope overburden gas, the division difficulty of extraction area, and the problem of rear gob fire difficult governance. And the overburden porosity distribution during caving is one of the main factors causing the flow field maldistribution. The model of long wall top-coal caving is established with the relationship between elastic modulus, Poisson ratio, compressive strength, and tensile strength with microscopic parameters of rock, which is on the basis of the geological column of one mine in Inner Mongolia and using the Bonded Particle Model (BPM) in Particle Flow Code (PFC^2D). Analyzing the failure process, the failure mode and the failure range of excavating overburden strata, the vertical stress evolutionary process of rock mass in coal seam roof and floor and the evolution laws of porosity are recorded during the course of the stope moving. The results show that using PFC software simulates overburden strata failure process well, and the result corresponds to that simulated by FLAC.