Thermal gradient–dependent fracture behavior of ice-rich frozen soils

Fractures in frozen soils are strongly associated with thermal gradient–dependent heterogeneity and significantly affect frost heaving and thaw subsidence in permafrost by altering the soil structure and the moisture migration path. An experimental study was conducted to investigate the quantitative relationship between fracture behavior and stress-induced heterogeneity of frozen soils with a thermal gradient. A series of visualization-aided unconfined compression tests on frozen soil columns with a thermal gradient under various water contents and temperatures was performed. The results indicated that the influences of water content and temperature on the observed fracture can be unified into an heterogeneity level. An increase in the heterogeneity level weakened the peak strength and enhanced the volumetric dilation of the frozen samples. The strain localization zone was the main location for fracture initiation and development, and its range accounted for over 70% of the fracture. The height of the fracture reduced with stress-induced heterogeneity level increased, while its reducing rate was over 2 times more than that of the maximum lateral deformation and strain localization zone. A mean asymmetry coefficient over 1.2 in the heterogeneity level observed at the two sides of the frozen specimens was attributed to the occurrence and change in location of the shear fracture. These observations and findings have significant importance for development of a fracture model that incorporates the influences of stress-induced heterogeneity in frozen soils with a thermal gradient to improve the mathematical formulations on frost heave.