Characterization and dynamic evolution law of transverse fractures in the upper protected coal seam.

Taking prefabricated coal briquettes as fracture test units, a similar physical simulation experimental platform equipped with a flexible loading device was established to investigate the dynamic evolution mechanism of transverse fractures in the upper protected coal seam. In-situ-like CT scanning three-dimensional imaging technology was employed to extract the internal transverse fractures of coal samples and their distribution patterns, while the evolution law of transverse fractures was analyzed using fractal dimension and fracture angle. The ABAQUS finite element software was utilized to establish a transverse fracture evolution model, aiming to study the variation laws of stress, displacement, and subsidence displacement of overlying strata after mining. The subsidence characteristics of overlying strata in the coal seam were obtained, and the dynamic evolution of overlying strata was divided into three stages: roof separation failure, fracture and collapse stage, overlying strata destruction stage, and destruction stabilization stage. This study provides key theoretical basis and data support for the accurate characterization of dynamic evolution of transverse fractures during the mining of upper protected coal seams, the analysis of evolution laws of gas migration channels, and the scientific formulation of targeted gas extraction schemes.