A Study on Macro and Micro Characteristics and Correlation of Soil under Cyclic Freeze–Thaws

Abstract

When soil is subjected to freeze–thaw cycles, its macro morphology and overall strength experience certain changes that often are caused by microscopic modifications of its internal structure in geological hazards. To clarify the relationship between the microstructure characteristics and the macro deformation of silt under cyclic freeze–thaws, eight silt samples with different compactions and moisture contents were set up to conduct five cycles and computed tomography (CT). The displacement and CT images of the soil were obtained. The displacement monitoring results show that there was a relationship between compaction and moisture content, which determined whether the silt experienced a settlement or an expansion. To capture the quantitative microstructural characteristics from the CT images, the two-dimensional threshold histogram method was improved, and the threshold values between fracture and soil units in the freezing and thawing states were found. Furthermore, six microstructural parameters of fractures were obtained. Through correlation analyses, the relationship between the microstructural parameters and soil displacement was verified to be similar to that between the physical parameters and the displacement. In addition, an exponential statistical model of micro and macro parameters was established, showing that the soil microstructure can be improved, and the displacement is constrained within a relatively tight bound after cyclic freeze–thaws.