Promoting effect and microscopic mechanism of train-induced vibration on loess disintegration

Loess disintegration aggravates slope erosion and triggers hazards such as spalling, landslides, and mudflows. Long-term vibrations along railways can change the microstructure of the loess, thereby affecting its disintegration characteristics. However, few studies have considered the effects of long-term vibrations caused by trains on the disintegration of intact loess. This study conducted disintegration tests on loess subjected to prolonged vibrations at varying frequencies to analyse the differences in the disintegration behaviour. Using scanning electron microscopy (SEM) and soil-water characteristic curve (SWCC) tests, this study characterised the microstructural changes in loess before and after vibration to reveal the mechanism by which train-induced vibration affects loess disintegration characteristics. The results indicated that train-induced vibrations expedited the loess disintegration process, improving the disintegration efficiency and the dispersion degree of the disintegrated soil. Overall, higher vibration frequencies were associated with a more pronounced promoting effect on disintegration in the 0-25 Hz range. Three distinct stages of disintegration evolution based on a growth model were identified quantitatively, and the effect of vibration frequency on the disintegration acceleration at each stage was quantificationally analysed. The train-induced vibration decreased the duration of the initial two stages of disintegration and notably increased the disintegrated mass, thereby significantly improving the overall disintegration efficiency. The promoting effect of loess disintegration by train-induced vibration was attributed to increased suction imbalances caused by heightened pore differentials after vibration, as well as reduced particle occlusal and cementation forces caused by particle abrasion and the loosening of weakly cemented aggregates. These factors combine to accelerate the imbalance between the disintegration and resistance forces. These findings provide beneficial insights into the potential hazards of loess slopes exposed to long-term train vibrations.