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Freeze–thaw cycles can deteriorate the expansive soil performance. Phase change materials (PCMs) absorb and store heavy latent heat from the environment, which can be utilized to mitigate freeze–thaw deteriorations in expansive soil. In this study, an environmentally friendly paraffin-based PCM was selected, which included two different forms: liquid (pPCM) and microcapsules (mPCM). The volume change, mechanical properties, thermal properties, and microstructure of the improved soil were studied. These results showed that PCMs can release considerable thermal energy during phase transitions, which improves the thermal stability of the soil. The pPCM enhanced the plasticity of soil and prevented brittle failure; mPCM reduced the damage to the soil microstructure caused by freeze–thaw cycles. Macroscopically, it weakened the swell–shrink behavior and limited the degradation of the resilient modulus, unconfined compressive strength, and failure strain of expansive soil. The optimal PCM content was determined based on the mechanical and thermal properties of the improved soil. This study provides a new idea for the engineering treatment of expansive soil in cold regions. [ABSTRACT FROM AUTHOR]

The thermal state of permafrost in the present and future is fundamental to ecosystem evolution, hydrological processes, carbon release and infrastructure integrity in cold regions. In 2011, we initiated a permafrost monitoring network along the China–Russia crude oil pipeline (CRCOP) route at the eastern flank of the northern Da Xing'anling Mountains in Northeast China. We compiled an integrated dataset of the ground thermal state along the CRCOP route consisting of meteorological data near the southern limit of latitudinal permafrost, ground temperature (GT) data in 20 boreholes with depths of 10.0–60.6 m, soil volumetric liquid water contents (VWCs) and 2D electrical resistivity tomography (ERT) data at different sites. Results demonstrate a permafrost warming during 2011–2020 in the vicinity of the southern limit of latitudinal permafrost, as manifested by rising GTs at almost all depths in response to climate warming. Local thermal disturbances triggered by the construction and operation of CRCOPs have resulted in significant permafrost warming and subsequent thawing on the right-of-way (ROW) of the pipelines. This permafrost thaw will persist, but it can be alleviated by adopting mitigative measures, such as an insulation layer and thermosyphons. The in situ observational dataset is of great value for assessing the variability of permafrost under the linear disturbances of the CRCOPs and related environmental effects, for understanding hydro–thermal–mechanical interactions between the buried pipelines and permafrost foundation soils, and for evaluating the operational and structural integrity of the pipeline systems in the future. The dataset is available at the National Tibetan Plateau/Third Pole Environment Data Center (10.11888/Cryos.tpdc.272357; Li, 2022). [ABSTRACT FROM AUTHOR]

Thermal insulating materials (TIMs) are widely used in roadways, tunnels, airfields, pipeline systems, and buildings in cold regions to prevent infrastructure from freeze damages and reduce energy consumption. During the period of use in cold regions, however, seasonal freeze-thaw actions can cause degradation of thermal and mechanical properties of TIMs and even malfunctions. Lots of research has been carried out on the durability of TIMs under cyclic freeze-thaw (CFT), but comprehensive reviews are scarce at present. Based on a literature review, the state and development of the test apparatus, temperature controls for the CFT test, and changes in the thermal and mechanical characteristics of TIMs during the CFT operations were summarized in this study. The review shows that the CFT can damage the TIMs' microstructure, which will result in an increase in the materials' thermal conductivity and water absorption rate with a decrease in their mechanical strength. However, since the application scenarios of TIMs are various, there are significant differences in previous researches, especially the test conditions. These differences limited the applicability of the test results and make a barrier among researchers and engineers. Thus, a unified test method for the durability of TIMs under the CFTs should be established in the future. [ABSTRACT FROM AUTHOR]

Freeze-thaw interface in unsaturated coarse-grained soil (CGS) is a weak plane which can cause slope failures in cold regions. This study presents a series of large-scale direct shear tests on freeze-thaw interface in CGS through a temperature control system. The tested soil was taken from a high slope in the Qinghai-Tibet Plateau. It was remolded with three dry densities (1.9, 2.0, and 2.15 g/cm3) and three moisture contents (9.0%, 11.5%, and 14.0%). With testing results, direct shear curves mainly performed as hardening deformation, and they were affected considerably by specimen conditions. The shear strength increased with both the increasing dry density and normal stress, but it was opposite with moisture content changed. The cohesion and internal friction angle increased with the increase in dry density but decreased with the moisture content. The particle movement and water migration of freeze-thaw interface in CGS during the test were significant, and they had close relations with the shear properties of specimens. And, an empirical model was produced to express the effect of pore ice on the shear strength of interface during the shear test. The tests and analysis in this study may provide useful references for CGS slope stability analysis in high cold regions. [ABSTRACT FROM AUTHOR]

Frost heave of soils involves complex coupled interactions among moisture, heat, and stress, which can cause serious damage to cold regions engineering. In this paper, a series of one-directional freezing experiments were implemented for the Tibetan clay with rigid restraint in an open system. The varying characteristics of the temperature, frost-heaving force, and water replenishment during the freezing process were analyzed under different freezing temperatures (−5, −7, and − 9°C), dry densities (1.65, 1.7, and 1.75 g cm−3), and initial moisture contents (11, 14, and 17%) of the soil samples. It was concluded that the freezing of soil samples mainly occurred within 10–25 hours from the beginning of the experiment; hereafter, the soil temperatures tended to be stable. The development of frost-heaving force could be divided into three stages as slow increase, quick increase, and relative stable stages. Low freezing temperature, large dry density, and high moisture content were all the contributors to the frost-heaving process of the soil, which could increase the freezing depth, magnitude of the frost-heaving force, and amount of water replenishment. The variations in water replenishment from the open system corresponded to the three stages of the frost-heaving force but had time lags. The moisture contents at different layers of soil samples were measured after the freezing experiment. The results showed that the freeze part of soil samples experienced a significant wetting, while the unfrozen part experienced drying during the experiment. The degrees of wetting and drying were related to the freezing temperature, dry density, and initial moisture content of the soil samples. The experiment results could provide data support for theoretical study on moisture, heat, and stress coupling in freezing soil. [ABSTRACT FROM AUTHOR]

The shear behavior of a frozen soil-structure interface plays a vital role in analyzing the performance of engineered structures in cold regions. This study investigates the freeze-thaw cycling impact on the shear behavior of a frozen soil-concrete interface by direct shear tests. Test specimens consisting of a Portland cement concrete disk and frozen loess with an initial moisture content ranging between 9.2% and 20.8% were prepared and conditioned at various sub-zero temperatures (i.e., −1 °C, −3 °C, and − 5 °C) and freeze-thaw (F-T) cycles (i.e., 0, 5, 10, and 20). Experimental results, including shear stress - horizontal displacement curves, the displacements and shear strengths at both peak and residual status, are presented and analyzed. In particular, the influence of F-T cycling on shear behavior is examined. The peak displacement is found to increase linearly with increasing initial moisture content, but their correlation weakens as the number of F-T cycling increases. However, the residual displacement is found to be insensitive to the initial moisture content, temperature, normal stress, and F-T cycling. While the residual friction angle is slightly larger than the peak one before F-T cycling, both gradually increase with an increasing number of F-T cycling. Large cohesion in the peak strength, especially at lower temperatures, completely diminishes in the residual strength due to damage of ice bondage, resulting in a significant shear strength loss between the peak and residual status. The impact of F-T cycling on the interface shear behavior can be attributed to moisture migration toward, formation and accumulation of ice films at the interface. The findings from this study including the shear strength parameters and the displacements at both peak and residual status, can be used to simulate the performance of engineered geotechnical assets such as pile foundations, retaining walls, and earth dams or irrigation channels with concrete linings in cold regions. • Investigate the shear behavior of a frozen soil-concrete interface. • Focus on both shear strength and displacement characteristics. • Examine F-T cycling impact on the shear displacement and strength parameters. • Present key parameters for the simulation of the interface shear behavior. [ABSTRACT FROM AUTHOR]

In winter, cold air flowing into tunnels undergoes heat exchange with the surrounding rock and lining, rendering frost protection a critical concern. In this paper, a practical procedure for integrating the FEM–CFD coupled method into probabilistic analysis is presented for determining the thermal insulation length demand of tunnels in cold regions, in which uncertainties in the air temperature and wind speed are considered. The results indicate that with ventilation implemented in the coldest month, tunnel temperatures gradually rise along the longitudinal direction, exhibiting a distinct temperature variation near the entrance. Based on the numerical simulation results obtained with 100 air temperature and wind speed samples, generated using the Monte Carlo method, the thermal insulation length demand of the tunnel ranges from 1000 to 1500 m, showing a distribution that follows the characteristics of a normal distribution. Additionally, a corresponding surrogate model is developed, and a thermal insulation failure probability model is proposed to analyze the sensitivity of meteorological parameters, revealing that the air temperature is the primary factor influencing the thermal insulation length demand. The findings of this research provide novel insights for the engineering community in designing resilient and sustainable tunnels in cold regions, mitigating the potential risks associated with freezing events and ensuring safe and efficient transportation infrastructure. • Probabilistic models for air temperature and wind speed were proposed. • Uncertainties of air temperature and wind speed affect thermal insulation length. • A surrogate model of the thermal insulation length demand was developed. • An analysis of the thermal insulation failure probability was conducted. [ABSTRACT FROM AUTHOR]

In cold and arid regions, the maintenance of roadways and railways faces significant challenges due to serious spalling and sheet erosion, rill erosion, and shallow sliding of loess slopes. Moreover, the frequency and severity of these shallow failures, as well as the vegetation cover, differ greatly between sunny and shady slopes, further complicating slope maintenance. This study focuses on field observations conducted over two consecutive years along a highway at the western end of Chinese Loess Plateau, specifically examining soil temperatures and moisture content within two cut slopes. By analyzing the differences in hydro-thermal regimes within a depth of 100 cm between the sunny and shady slopes, and considering the meteorological data collected at the study site, the research aims to provide insights into these failures of loess slopes. The results indicate that the shady slope undergoes significant seasonal freeze-thaw cycles from the surface down to a depth of 100 cm. The freezing duration ranges from 96 to 120 days, with a freezing index ranging from −250 °C·d to −850 °C·d. Additionally, the shallow layer on the shady slope experiences significant daily freeze-thaw cycles in late autumn and early winter. In contrast, the sunny slope experiences minimal seasonal freeze-thaw processes. Although the shallow surface layer of the sunny slope undergoes some daily freeze-thaw cycles in late winter and early spring, the amplitudes of soil temperature fluctuations are significantly smaller compared to those on the shady slope. Given that the precipitation is concentrated in summer and autumn, the moisture content of the soil on the shady and sunny slopes exhibits noticeable seasonal changes. The soil layers on the shady slope tend to be relatively dry, while those on the sunny slope remain relatively moist. The moisture content within the observed depth on the sunny slope remains relatively consistent, while on the shady slope, a clear gradient is evident. The moisture content of the shallow slope layers within a depth25 cm primarily responses to heavy rainfall events, with a greater response observed on the shady slope compared to the sunny slope. The field-observed hydro-thermal data collected in this study serve a valuable basis for implementing revegetation strategies and enhancing the stability of loess slopes in cold and arid regions. • Hydro-thermal regimes of sunny and shady cut slopes were observed in loess regions. • Seasonal and daily freeze-thaw of sunny and shady cut slopes were compared. • Dry-wet cycles of sunny and shady cut slopes were compared. • Response of soil moisture content of slopes to rainfall events were discussed. [ABSTRACT FROM AUTHOR]