Disintegration Mechanism of Coal-Bearing Soil Based on Granularity Entropy and Water–Air Two-Phase Flow

Coal-bearing soils (CBS), products of coal-bearing strata weathering, are particularly prone to disintegration due to the effects of dry-wet cycles. Static water disintegration tests, environmental scanning electron microscopy (ESEM), and mineral chemical composition analyses were conducted on CBS. The disintegration evolution of CBS is characterized by granularity entropy and is analyzed concerning the disintegration ratio. Furthermore, the disintegration mechanism is examined based on the water-air two-phase flow (WTF) and mineral chemical reactions. Results show a significant exponential relationship between the standard basic entropy (A) and disintegration ratio (D_R), where the disintegration ratio decreases as the standard basic entropy increases. As the number of dry-wet cycles increases, A initially decreases rapidly before stabilizing, mirroring the variation pattern of the particle size distribution curve and its derived indicators. Illite produces significant short-range hydration repulsion, leading to the formation of additional cracks in CBS. WTF significantly influences disintegration; water intrusion increases air pressure, and the subsequent pressure release plays a critical role in damaging soil structure. These findings are significant for the safety and protection of CBS slope engineering.