Skeleton Structure of Segregated Ice Lenses in Frozen Soil and Its Effects on the Mechanical Properties

Clarifying the relationship between frozen soil strength and its internal structure is essential for predicting frozen soil properties. Due to the limitations in testing and observation methods, there is a lack of quantitative analysis regarding the structure of segregated ice in frozen soil. Therefore, a series of uniaxial compression tests and computerized tomography (CT) scans were performed on frozen clay containing abundant segregated ice to analyze the characteristics and the effects of the ice structure. Based on the compression tests, the presence of the ice structure increases the strength of the frozen clay by approximately 70%, confirming the reinforcing effect of the ice structure on strength. According to CT scan results, the segregated ice within the soil forms a skeletal structure interconnected by ice lenses and ice wedges, and the morphological characteristics of this skeleton are related to the freezing depth. To quantify the evolution of this ice skeleton, five parameters were introduced, and expressions of these parameters with freezing depth were established. The area of the polygon enclosed by the ice wedge (which is correlated with the side length) and the thickness of the ice wedge increase linearly with freezing depth, while the spacing and thickness of ice lenses tend to increase with significant fluctuation. The mechanism of this evolution is effectively explained by the periodic consolidation of soil caused by negative pore-water pressure during the formation of ice lenses. Finally, a simplified model of the ice skeleton is proposed, featuring a distinct tower-like profile with walls that thicken from top to bottom and a middle section composed of plates that are dense at the top and become loose toward the bottom. This structural feature of the ice skeleton is an important source of the high strength of frozen soil, which holds significant implications for the active utilization of frozen soil.