Microscale Investigation of Aggregate Stability Characteristic and Pore Structure of Collapsing Wall in Granite Red Soil

Benggang is a special large‐scale erosion landform distributed in the granite red soil area of southern China, and the complex and stochastic secondary erosion processes induced by the instability of collapsing walls lack systematic explanation. Research on this from a microscopic perspective may be the key to solving this challenge. In this study, x‐ray computed tomography was used to analyze aggregate stability and the internal pore characteristics of 18 soil depths collected along a complete collapsing wall. The results revealed considerable vertical differences in soil properties. The mechanically stable aggregates and water‐stable aggregates were mainly in the > 2 mm and < 0.25 mm particle size ranges, respectively. The disaggregation reduction (DR) value obtained via ultrasonication can reasonably characterize the cohesive ability of aggregates in coarse‐textured soils and was significantly positively correlated with the soil mechanical properties. The medium and micro pores (especially < 30 μm) occupied more than 95% of the pore space among the soil aggregates. The morphological parameters characterizing the pores, including length, tortuosity, diameter, surface area, volume, and sphericity, increased significantly with increasing soil depth and stabilized after reaching 285–315 cm, implying that the pore functionality varied along the collapsing wall. Soil organic matter (SOM) explained 74.4% of the variation in aggregate stability, followed by the proportion of < 30 μm aggregate pores and sphericity, indicating that cementing materials dominated and that the pore distribution and morphology jointly affected soil aggregate stability. Therefore, the variability of the aggregate stability and pore structure in the collapsing wall may be key influencing factors for secondary Benggang erosion.