Assessing the impact of retrogressive thaw slump on soil structure by analyzing the multifractal characteristics of soil particle size distribution on the Qinghai–Tibet Plateau

Climate warming has intensified retrogressive thaw slumps (RTS) in permafrost regions of the globe, especially in the Qinghai–Tibet Plateau (QTP), resulting in severe soil erosion. Evaluating their impact on soil structure is vital for comprehending local ecological shifts and ensuring engineering stability. In this study, soil samples were collected from different depths in different positions from a RTS on the QTP, after which the concentration, uniformity, and symmetry of the soil particle size distribution (PSD) were quantified via multifractal theory. The results showed that the erosion depth of the RTS was less than 40 cm by comparing the differences in the multifractal dimensions of the soil at different depths between the undisturbed and eroded areas. The erosion effects of the RTS led to an increase in the degree of variation in the soil in the vertical direction and the fine graining of the soil. The soil heterogeneity in the eroded area initially sharply increased, followed by a gradual decrease. The PSD of eroded soil tended to be more concentrated in certain specific sub ranges, resulting in an increase of local heterogeneity of soil structure and a decrease of the soil shear strength. The multifractal parameters, including D₁/D₀ and Δα are recommended as indicators for quantitatively evaluating the erosion effects on soil structure from the retrogressive RTS on the QTP.