Investigating the Evolution of Coal Pore Structure Triggered by Fault Activation

To investigate the quantitative relationship and dynamic response evolution between fault activation and coal pore morphology, this study employs coal samples from faults with varying throws to simulate the fault throw activation process. Taking the 120910 working face of the Longfeng Coal Mine in Guizhou as the study area, six groups of coal samples with gradient throws were collected. High-pressure mercury intrusion porosimetry (MIP), low-temperature nitrogen adsorption (LTNA), and fractal theory were integrated to systematically reveal the evolutionary characteristics of coal pores driven by fault activation. The results indicate a three-stage dynamic evolution characterized by distinct critical thresholds. (1) In the initial fracture development stage corresponding to fault throws not exceeding 1.2 m, fault activation promotes the propagation and coalescence of primary fractures, manifested as slight increases in specific surface area and pore volume. (2) As the throw increases to 1.2–1.6 m, corresponding to the strong compaction stage, intense compression triggers extensive collapse of pore throats ranging from 2 to 50 nm, resulting in a sharp 57.8% decline in specific surface area and the poorest pore connectivity; (3) When the throw exceeds 1.6 m and the process enters the secondary fracturing stage, the coal undergoes brittle failure, generating abundant ultrafine pores. This drives an exponential rebound in specific surface area and increases the micropore volume to 0.0069 m3/g, indicative of significant pore refinement. Collectively, this evolutionary process exhibits a three-stage dynamic pattern of “fracture development-strong compaction-secondary fracturing” with well-defined critical points. This study elucidates the pore structure evolution characteristics of coal during fault activation, providing guidance for safe gas drainage and coal and gas outburst prediction.