Shrinkage characteristics of red clay on the Qinghai-Tibet Plateau under freeze-thaw cycles

The increasing trend toward warmer and wetter climatic conditions on the Tibetan Plateau has heightened the risk of rainfall-induced landslides in areas where red clay is widely distributed. This study aims to investigate the evolution of shrinkage characteristics of red clay from the Nangqian area of the Qinghai-Tibet Plateau under repeated freeze–thaw cycles through the direct measurement method. The results show that the freeze-thaw cycle causes the initial structure of the soil to be destroyed and reorganized, resulting in volume shrinkage. After four freeze–thaw cycles, the volume of the sample shows a recoverable expansion and contraction change. With increasing freeze–thaw cycles (N), the shrinkage characteristic curves of the two initial dry density specimens gradually shift upward, the slope of the proportional shrinkage section significantly decreases, and the curves tend to coincide at N=5 and N=7. Meanwhile, the fitting parameters a and b of the Fredlund model have smaller numerical fluctuations when N=7, indicating that the influence of freeze–thaw cycles on soil shrinkage tends to be stable after approximately seven cycles. The freeze-thaw cycle causes structural shrinkage segments in the two initial dry density specimens, and the structural limits are approximately 0.77 and 0.68, respectively. This study provides a theoretical basis for the prevention of freeze-thaw disasters in plateau areas.