Air escape and disintegration behaviors of granite residual soil

In recent years, extreme rainfall events have triggered widespread geological hazards in granite residual soil (GRS) areas, posing significant risks to human safety. Such geological disasters are closely linked to the disintegration behavior of GRS. Although pore air escape during soil disintegration has been widely observed, its effect and underlying mechanism remain unclear. Moreover, existing experimental methods are unable to capture the true disintegration state of soil particles. In this study, the conventional disintegration apparatus was improved by incorporating an air collection device to capture escaped air during testing. Based on this modification, an equation for calculating the disintegration rate ( ), which reflects soil particle loss, was derived. Additionally, equations for the air escape rate ( ) and air escape velocity ( ) were established. Disintegration tests were conducted on remolded GRS specimens with varying initial moisture contents ( IMCs ), allowing monitoring of disintegration morphology, , and pore air escape characteristics during the process. The results indicate that the complete disintegration time of soil samples decreases with increasing IMC . Based on disintegration and pore air escape characteristics, the disintegration behavior of samples with different IMCs was classified into three types. (1) CDS-A: complete disintegration with air-induced disintegration stage; (2) CDS: complete disintegration without direct air influence in the early stage; (3) CDR: uniformly rapid disintegration throughout. The pore air escape behavior and its role in promoting disintegration were further analyzed from a microscopic perspective using scanning electron microscope tests. Pore air primarily accelerates disintegration via two mechanisms: forming air escape channels and directly pushing soil particles. Based on these mechanisms and the observed variations in , the study analyzed the reasons behind the differences in disintegration behavior among samples with varying IMCs . These findings provide a scientific basis for understanding the disintegration mechanisms of GRS and the relationship between soil disintegration behavior and geological disasters.