Mechanism of thaw settlement induced by segregated ice melting based on a visualizing study

The melting of segregated ice in ice-rich frozen soils is a primary driver of soil structural instability and thaw settlement, yet the dynamic morphological evolution of segregated ice and its quantitative linkage to thaw settlement remain poorly understood. To address this issue, a series of physical model experiments were conducted using a self-developed visualized thaw settlement experimental platform for ice-rich frozen soils. Thus, the different surface thawing temperatures (5 °C, 7 °C, and 10 °C) , multiple particle-size gradation schemes (G-I to G-V), and different external load levels (0.5 kPa, 1.0 kPa, and 1.5 kPa) were introduced to investigate the influence of temperature, gradation, and pressure on segregated ice melting and thaw settlement behavior. The results indicate that the melting process of segregated ice can be divided into a rapid phase-change stage and a stable thaw settlement stage. An increase in surface thawing temperature significantly shortens the duration of the phase-change stage and enhances downward migration of liquid water toward the unfrozen zone, resulting in a pronounced increase in thaw settlement. Particle-size gradation regulates moisture accumulation and migration by modifying pore structure and capillary force intensity; segregated ice is more readily formed in fine-grained soils, which exhibit a higher risk of thaw settlement after melting. External loading has a limited influence on the phase-change pattern; however, by increasing pore water pressure, it significantly intensifies settlement deformation during the stable stage. Pore structure collapse induced by segregated ice melting dominates the rapid settlement stage, whereas pore water drainage and soil skeleton reorganization govern deformation during the stable thaw settlement stage.