Freeze–thaw deformation of silty sand in the context of artificial ground freezing applications

Artificial ground freezing (AGF) is widely used for temporary ground improvement in underground construction. However, predicting freeze–thaw (FT) deformation remains challenging due to strongly coupled thermo-hydro-mechanical processes. Although applied vertical stress is generally expected to suppress frost heave, field observations continue to report significant ground movements. This study investigates the FT deformation of silty sand under controlled thermal and mechanical conditions, with particular emphasis on the role of applied vertical stress. FT tests were conducted in a temperature-controlled oedometer under vertical stresses ranging from 30 to 1000 kPa while varying cooling rate, temperature gradient, initial soil density, and stress history. Under low stress (30 kPa), thermal conditions and initial density strongly influenced deformation. Reducing the cooling rate increased frost heave by up to 44%, while increasing the temperature gradient from 0.4 to 0.65°C/mm amplified heave by 78%. Initial density controlled the post-thaw deformation state. Increasing the applied stress to 1000 kPa delayed freezing initiation, restricted water migration, and reduced frost heave from about 33% to 9%, substantially decreasing the influence of thermal and density effects. Overconsolidation partially reduced FT susceptibility, while extreme preloading increased frost heave, indicating that stress history cannot substitute for actively applied stress during freezing. Overall, the results show that FT deformation is strongly stress-dependent and provide practical guidance for AGF design and deformation risk assessment.