Keywords: Red Beds, moisture absorption expansion, non-uniformity, fracture, uplift, high-speed railway subgrade.

The sustained uplift deformation issue in high-speed railway subgrades in the Sichuan Red Beds region poses a long-term and potential threat to operational safety. Through reliance on practical engineering, this study conducts micro-fine-scale testing, triaxial expansion characteristic experiments, and in-situ layered uplift monitoring in the Sichuan Red Beds region. It analyzes the non-uniform expansion characteristics caused by differences in mineral composition, microstructural organization, and rock layer structure at different scales. The study explores the mechanism of its long-term uplift effect on the subgrade. The results indicate significant variations in the types and content of expansive clay minerals produced in the interlayers of the Sichuan Red Beds. Coupled with the preferential orientation of microscopic particles, this leads to high expansion force, a wide range of values, and noticeable anisotropy. This non-uniform expansion deformation creates macro-micro cracks, influencing the measured layered uplift quantity controlled by joint and fracture surface distribution. It is also identified as a crucial mechanism for the sustained non-convergent uplift deformation of the subgrade under the influence of repeated environmental changes. The research findings provide practical reference for high-speed railway construction and disease treatment in the Sichuan region.

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