Differences in Loess Wetting-Induced Deformation in Fuxian County Controlled by Mineral-Pore Coupling Effects

The study of the wetting-induced deformation mechanism of loess is of great importance for engineering disaster prevention and control in the Loess Plateau region. This research focuses on the Q₃p and Q₂p loess from Fuxian County, northern Shaanxi, aiming to reveal the deformation behavior and underlying mechanisms of loess from different geological eras under wetting conditions. A comparative study of the engineering properties of the two types of loess was systematically conducted through a series of physico-mechanical tests, mineral composition analysis, scanning electron microscopy (SEM) observations, and multi-condition consolidation-collapse tests. The results indicate that the consolidation deformation process of both types of loess can be divided into three stages: slow deformation under low pressure, accelerated deformation under medium pressure, and stabilized deformation under high pressure. Under high pressure conditions, the consolidation deformation becomes more sensitive to changes in initial water content. With increasing initial water content, the compression deformation of the Q₃p specimens intensifies significantly, while that of the Q₂p specimens weakens. In collapse tests, the two groups exhibited fundamentally opposite deformation characteristics: the Q₃p specimens showed typical collapse behavior, with the collapse coefficient initially increasing and then decreasing with rising pressure, whereas the Q₂p specimens displayed certain expansion characteristics. As the initial water content increased, the collapse coefficient of the Q₃p specimens gradually decreased, while the expansion tendency of the Q₂p specimens also weakened. Microstructural analysis revealed that the stability of the loess microstructure, particularly the presence of large pores, provides the necessary space for compression and collapse deformation. Mineral composition analysis indicated that the dissolution of soluble salt minerals (e.g., calcite) exacerbates soil compression and collapse deformation, while the water-absorbing expansion of clay minerals (e.g., illite) partially suppresses these behaviors. This study elucidates the controlling mechanism of the coupling effect between mineral composition and microstructure on the wetting-induced deformation behavior of loess, providing important theoretical support and practical guidance for engineering construction and geohazard mitigation in loess regions.