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This paper presents a comprehensive research about the coupled influence of freeze-thaw procedure and stress condition on cyclic mechanical properties of the frozen clay. According to cyclic test data of frozen clay at the temperature −10 °C, dynamic responses in various cases of confining pressures, cyclic loading amplitudes and freeze-thaw cycles are investigated in detail. Cyclic stress ratio is used to investigate the coupling effects of the freeze-thaw procedure, confining pressure and dynamic loading amplitude on permanent strain curves under same dynamic cycle-time. The permanent axial strain raises with increase of cyclic stress ratio. An empirical formula is presented to quantitatively characterize the coupled effects on the permanent deformation of frozen samples. Two-stage evolution features of resilient modulus in the cyclic loading process are clearly observed under all confining pressures and dynamic stress amplitudes. The inflection points of two-stage curves are rationally considered as the endpoints for the post-compaction compression stage. The axial strain value at this inflection point is defined as the yield strain under cyclic loading conditions. The yield strain point roughly occur around 3000th-3900th loading cycles. When the freeze-thaw cyclesreached at 6, the loading cycles at the inflection point (yield point) were approximate 3300. There was no obvious freeze-thaw cycle threshold for the dynamic elastic properties of frozen samples. Finally, based on the analysis for the loading cycle numbers at those yield points, the dynamic strength curves of samples under different confining pressures can be established. • Dynamic properties of frozen clay under freeze-thaw cycles were investigated. • Cyclic yield stress is determined based on two-stage evolution of resilient modulus. • Dynamic strength curve is both dependent on confining pressure and stress amplitude. [ABSTRACT FROM AUTHOR]

Research on the effect of snow on the temperature field of frozen ground is of great significance to the laying of underground oil pipelines, design of roads, and control of frost damage in cold regions. The heat transport laws of frozen ground with phase changes under periodic temperature boundary conditions were analyzed based on data monitoring in this paper. Based on the boundary conditions determined by the monitoring data, the numerical calculations of frozen ground and subgrade with/without snow cover were carried out, and the effects of snow cover on the temperature fields of frozen ground and subgrade in cold regions were explored. Monitoring results demonstrate that the temperature at different sections of frozen ground with phase change presents a sine-like function under the periodic temperature boundary condition. According to monitoring data, when the thickness of the natural surface snow cover is about 25 cm, the daily average minimum temperature of soil at 0.1 m from the surface will rise by about 10 °C compared to that without snow cover during a year (in a cycle); nevertheless, when combined with numerical calculation, the permafrost table increases by about 2.87 m, and the permafrost base decreases by more than 5.59 m. Under the boundary conditions set in this paper, the permafrost under the subgrade disappears in a greater area due to the construction of the subgrade in the snow-covered area. In addition, the elliptical thawing soil area produced by the lower part of the slope of a snow-covered subgrade will adversely affect its stability. • The mechanism of heat transfer of frozen ground under periodic boundary conditions was revealed in detail. • Change laws of the temperature field of natural frozen soil with and without snow cover were analyzed. • Effect of snow cover on the temperature field of subgrade and the reason for frost damage of subgrade were studied. [ABSTRACT FROM AUTHOR]

This paper investigated the freezing processes of Qinghai-Tibet silty clay within an added quartz sand layer (QSL) under different one-dimensional freezing temperature gradients by using computed tomography scanning and image acquisition technologies in an open system. The heat transfer, cryostructure formation and water migration processes and mechanisms were discussed. The results reveal that the temperature of the samples was essentially steady within 12 h, and the addition of the QSL has a significant impact on the temperature distribution in the samples. The moisture content of the QSL and the frozen part of the sample increased, while the moisture content of the unfrozen zone decreased significantly after being frozen for 120 h. The QSL was able to effectively limit liquid water migration, however, there was still vapor migration in the samples. Ladder-like and net -like cryostructures formed in the vertical sections of the sample while polygon cracks formed in the horizontal sections, which providing pathways for moisture migration. The saturated vapor pressure difference which calculated by the Antony Equation can be used as the driving force for vapor migration from the unfrozen zone to the frozen zone. From both an experimental and theoretical standpoint, this work is intended to aid research into the physical process and mechanism of sand interbedded stratum and foundation freezing. • The image acquisition and computed tomography scanning method were used to study the cryostructure of freezing soil. • Ladder-like and net-like cryostructures were formed due to the freezing temperature gradient. • The added quartz sand layer was able to effectively limit liquid water migration but there still vapor migration exists. • The polygon cracks formed in the horizontal sections of the soil samples, providing pathways for moisture migration. • The saturated vapor pressure difference provides the driving factor for vapor migration in the freezing soil. [ABSTRACT FROM AUTHOR]

Frost damage of soil foundations of engineering structures is controlled by mechanical properties of soil under frozen and unfrozen states, existing widely in cold regions such as Genhe area that is termed as the "pole of cold" in China. For investigating engineering properties of soil in cold regions, a series of triaxial compressive tests were carried out on both frozen and unfrozen Genhe silty clay with different degrees of compaction under different confining pressures. The test results show that the stress-strain curves gradually change from softening to hardening with increasing confining pressure, temperature and decreasing compaction degree. Additionally, both axial and radial deformation is more sensitive to lower confining pressures. An accurate method was proposed for determining the elastic modulus. The elastic modulus and strength decrease significantly as the state of soil changes from frozen to unfrozen. The effect of compaction degree on radial deformation, strength and failure strain is gradually eliminated with the increase of confining pressure, which can be observed in both frozen and unfrozen soil. The isotropic tensile strength and the cohesion were obtained in the stress spaces of p - q and σ - τ respectively, and the ice cementing force was identified by adopting the difference of the two strength parameters between frozen state and unfrozen state. The results indicate that the ice cementing force calculated by two strength parameters is consistent, which increases with increasing compaction degree. • The coupling effect of compaction degree and confining pressure was identified. • A method was proposed for accurately determining the elastic modulus under global strain measurement. • The restraining effect of confining pressure on radial deformation was quantified. • The ice cementing force was determined by two methods and the two results were consistent. [ABSTRACT FROM AUTHOR]