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Composite geotextiles are frequently utilized in water delivery canals and other projects in cold regions. However, the peak strength of the soil-geotextile interface can be degrade due to continuous wet-dry-freeze-thaw (WDFT) cycles, potentially compromising the stability of the infrastructure. This paper presents the use of a temperature-controlled direct shear system to conduct direct shear tests on the interface between the soil and the geotextile composite under a variety of normal pressures, temperatures, and WDFT cycles. The study shows that WDFT has minimal effect on the shear stress-shear displacement curve at positive temperatures. At negative temperatures, the curve transitions from strain hardening to strain softening. At negative temperatures, the average increase in peak strength was 39 %, 56.9 %, and 65.3 % after a single WDFT cycle at −2 °C, −6 °C, and −10 °C, respectively. A gradual decline in peak strength was observed with each subsequent cycle, although the peak strength remained slightly higher than the initial strength. The average growth rates were 6.6 %, 19.3 %, and 29.2 % after ten cycles, respectively. The interfacial cohesion and friction angle exhibited similar trends to those of peak strength. The sensitivity analysis revealed that temperature and WDFT cycles exert a considerable influence on the interface cohesion.

Buried pipelines have been widely used to transport petroleum-based products over long distances in permafrost regions. Field observations reveal that they are endangered by rapid permafrost thawing and resulting massive soil movements, despite adopting some measures to protect pipeline foundation permafrost. A new mitigation technique is proposed to slow down the permafrost thawing ulteriorly. With this technique, a seasonal air-cooled embankment (SACE), mainly composed of a crushed rock layer, supports the pipeline and transfers the heat from the pipeline to ambient air in the cold seasons. A scale model test with the controlled air and oil temperatures was carried out to evaluate the proposed measure. The temperature and volumetric unfrozen water content of the permafrost subgrade beneath both the SACE and the direct-buried pipeline, as well as ground surface displacements, were measured during the whole testing process. A comparison of the hydrothermal process of the subgrade permafrost under the SACE and the direct-buried warm pipeline indicates that the proposed measure can substantially mitigate the rapid thawing of permafrost by controlling the geothermal regimes of the pipeline.

Highways and their surrounding areas in mountainous and plateau regions are particularly susceptible to environmental changes, which can significantly impact their safety. In the context of global warming, the magnitude of environmental changes around highways has been further amplified. These environmental disturbances pose substantial risks to highway infrastructure in mountainous regions. By using satellite data and remote sensing techniques, this study focused on the environmental variations of the Du-Ku Highway (DKH) in the Tianshan Mountains and the preliminary revealed shifts in surface water, land surface temperature (LST), normalized difference vegetation index (NDVI), and temperature vegetation dryness index (TVDI) since 2000. The quantitative results showed that the water bodies with area between 0.1 and 0.5 ha showing the most significant growth around the DKH. The LST values are primarily distributed between 280 and 285 K, while the NDVI values are mostly below 0.4, and the TVDI is mainly concentrated at the two extremes. In the context of global warming and its amplified impact on mountainous and plateau regions, these findings offer critical insights that can directly support mountainous highway construction and maintenance strategies by identifying environmental indicators, providing a scientific foundation for making data-driven decisions.

The interface between soil and concrete in cold climates has a significant effect on the structural integrity of embedded structures, including piles, liners, and others. In this study, a novel temperature control system was employed to conduct direct shear tests on this interface. The test conditions included normal stress (25 to 100 kPa), temperature (ranging from 20 to −6 °C), water content (from 10 to 19%), and shear rates (0.1 to 1.2 mm/min). Simultaneously, the deformation process of the interface was continuously photographed using a modified visual shear box, and the non-uniform deformation mechanism of the interface was analyzed by combining digital image correlation (DIC) technology with the photographic data. The findings revealed that the shear stress–shear displacement curves did not exhibit a discernible peak strength at elevated temperatures, indicating deformation behavior characterized by strain hardening. In the frozen state, however, the deformation softened, and the interfacial ice bonding strength exhibited a positive correlation with decreasing temperature. When the initial water content was 16% and the normal stress was 100 kPa, the peak shear strength increased significantly from 99.9 kPa to 182.9 kPa as the test temperature dropped from 20 °C to −6 °C. Both shear rate and temperature were found to have a marked effect on the peak shear strength, with interface cohesion being the principal factor contributing to this phenomenon. At a shear rate of 0.1 mm/min, the curve showed hardening characteristics, but at other shear rates, the curves exhibited strain-softening behavior, with the softening becoming more pronounced as shear rates increased and temperatures decreased. Due to the refreezing of interfacial ice, the residual shear strength increased in proportion to the reduction in shear rate. On a mesoscopic level, it was evident that the displacement of soil particles near the interface exhibited more pronounced changes. At lower shear rates, the phenomenon of interfacial refreezing became apparent, as evidenced by the periodic changes in interfacial granular displacement at the interface.

Soil properties play a crucial role in the stability of engineering foundations, particularly in cold regions where temperature gradients impact water migration and soil conditions. This study utilized MRI-Cryogenic Soil-Moisture Analyzer (MRI-CSMA) to conduct indoor freeze-thaw experiments on silty clay specimens with varying initial water contents (12.0 %, 16.8 %, and 21.1 %). Dynamic changes in water content and temperature at different soil depths were analyzed. The results revealed distinct stage decrease characteristics in both temperature and water content as freezing progressed, with more pronounced changes closer to the cold end. Conversely, during thawing, temperatures and water content gradually increased as the boundary temperature rose. Notably, after the freeze-thaw cycle, the frozen zone consistently retained higher water content than the unfrozen zone, indicating water redistribution, regardless of initial water content levels. Furthermore, in three soil samples with different initial water contents, the water migration flux in the unfrozen soil layer decreased exponentially as freezing time increased. This phenomenon can be attributed to the combined effects of water boundary conditions, temperature gradients, and soil structure changes during soil freezing. These findings are likely to have significant implications for understanding water-heat dynamics in cold region soils as well as ensuring the stability of engineering projects.

The shear characteristics of the soil-geosynthetic interface are the primary factors affecting the load transmission rules. The interfacial shear parameters are affected by cycles of freeze-thaw and alter as a result of the periodic temperature fluctuations. Using an enhanced temperature-controlled direct shear apparatus, this paper investigates the interfacial shear characteristics between silty clay and composite geotextile according to freeze-thaw cycles. Analysis is done on how the interfacial stress-strain relationship, strength, and strength characteristics are affected by the soil moisture content, normal pressure, and test temperature. The results demonstrate that at low freezing temperatures and high moisture contents, the interfacial stress-strain curve is strongly influenced by cycles of freeze-thaw, and that the interfacial shear strength tends to grow initially before decreasing as the number of freeze-thaw cycles increases. The variations in interfacial shear strength correlate to the changes in interfacial friction angle and interfacial cohesion, and the primary element influencing the variation of shear strength is the alteration in interfacial cohesion. With a high soil moisture content initially, the migrating water has greater effect on shear strength during the freeze-thaw cycle. The findings of the significant level research indicate that the moisture content has a significant influence on the shear strength.

To study the effect of area-to-volume ratio on the dissolution and deterioration characteristics of sandstone in the static acid-rock reaction system, the HCl and H2SO4 solutions with pH=2 and 5 are selected as corrosion environments, and the different area-to-volume ratios are set by changing surface areas of sandstone. The effects of area-to-volume ratios on the physicochemical and mechanical properties of sandstone are studied. According to the acid-rock reaction theory, the effect of the area-to-volume ratio on the diffusion-dissolution mechanism during sandstone corrosion is analyzed. The results show that the sandstone mass loss rate and amount of substance of total cations are all related to the corrosion time as a power function. The area-to-volume is positively correlated with the dissolution rate constant and has little effect on the reaction order. The reaction order is less than one in different environments, indicating that the sandstone corrosion rate decreases gradually with soaking time. In the pH=2、5 HCl solution and pH=2 H2SO4 solution, the amount of substance of cation shows N(Ca2+) > N(Na+) > N(Mg2+) > N(K+), and in the pH=5 H2SO4 solution, it is N(Na+) > N(Ca2+) > N(Mg2+) ≈N(K+). The acid-rock reaction can be summarized as two mechanisms: diffusion control and chemical reaction control. The two control parameters are negatively correlated with the area-to-volume ratio and positively with the pH value of solutions. The parameter values in the H2SO4 solutions are slightly larger than the corresponding values in the HCl solutions. The interaction between sandstone and acid in different conditions is dominated by the chemical reaction. The area-to-volume ratio significantly influences diffusion more than the chemical reaction. The mechanical properties of sandstone are weakened after acid corrosion. The damage of sandstone under uniaxial compression can be divided into four stages: compaction, elastic deformation, plastic yielding and post-peak. The peak strength and elastic modulus decrease, the peak strain increases, the brittleness declines, and the ductility is enhanced. The larger the area-to-volume ratio, the more severe the sandstone deterioration is. Overall, the smaller the pH value of solutions, the more prominent the effects of the area-to-volume ratio on the dissolution characteristics and mechanical properties of sandstone are, which is more obvious in the HCl solutions than in the H2SO4 solutions. The finding can provide theoretical references for the safety assessment and disaster prevention of rock mass engineering under an acidic environment.

The water bodies existing along highways in the high altitude areas of the Qinghai–Tibet Plateau (QTP) will aggravate subgrade settlement and road damage, and affect the long-term stability of road networks. Based on remote sensing and geographic information system (GIS) techniques, this study analyzed the changes in the number and area of water bodies along the G109 and G219 highways in the QTP in the past 20 years. The results showed that between 2000 and 2019, the number of water bodies along the two highways increased by 24 and 19%, respectively, and their area increased by 26 and 19%, respectively. The area and the number of water bodies >1 km2 in the permafrost area and those

Crushed rock layers (CRLs), ventilation ducts (VDs) and thermosyphons are air-cooling structures (ACSs) widely used for maintaining the long-term stability of engineered infrastructures in permafrost environments. These ACSs can effectively cool and maintain the permafrost subgrade’s frozen state under climate warming by facilitating heat exchange with ambient air in cold seasons. As convection is a crucial working mechanism of these ACSs, it is imperative to understand the near-surface wind flow (NSWF) across a constructed infrastructure, such as an embankment. This article describes a yearlong field observation of the NSWF across an experimental expressway embankment, the first of its kind on the Qinghai–Tibet Plateau (QTP). The wind speed and direction along a transect perpendicular to the embankment on both the windward and leeward sides and at four different heights above the ground surface were collected and analyzed. The results showed that the embankment has a considerable impact on the NSWF speed within a distance of up to ten times its height, and in the direction on the leeward side. A power law can well describe the speed profiles of NSWF across the embankment, with the power-law indices (PLIs) varying from 0.14 to 0.40. On an annual basis, the fitted NSWF PLI far away from the embankment was 0.19, which differs substantially from the values widely used in previous thermal performance evaluations of ACSs on the QTP. Finally, the significance of the NSWF to the thermal performance of the ACSs, particularly the CRLs and VDs, in linear transportation infrastructure is discussed. It is concluded that underestimating the PLI and neglecting wind direction variations may lead to unconservative designs of the ACSs. The results reported in this study can provide valuable guidance for infrastructure engineering on the QTP and other similar permafrost regions.

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.

To carry out engineering construction in a permafrost area, it is of great importance to grasp the spatial distribution of permafrost and its hydrothermal characteristics within the scope of engineering activities. Compared with the continuous permafrost area, the permafrost distribution in discontinuous permafrost area is complicated due to existence of island talik, which causes highly poor continuity and uniformity of ground hydrothermal conditions and brings great difficulty and uncertainty to the engineering geological investigation. In the present study, the spatial distribution of permafrost and the freeze-thaw process of shallow ground at the I-stage terrace of a river on the Qinghai-Tibet Plateau were studied based on field investigation including drilling, electrical resistivity tomography, and borehole temperature measurement. The results show that the relict permafrost, patchy permafrost, and island talik are distributed in the limited range of the study area. Among them, the buried depth of relict permafrost layer is in the range of 7 ~ 14 m, while the patchy permafrost layer is in the range of 3.0 ~ 17.0 m depth, and the mean annual ground temperature of both is close to -0.1°C, which belongs to extremely high-temperature permafrost. The seasonal freezing/thawing depths of shallow ground within the relict permafrost, patchy permafrost, and island talik range from 2.5 to 3.0 m. The freezing period of the seasonal freezing layer is 5.5 months, while the thawing period of the seasonal thawing layer is 6 months. The complex plane and spatial distribution of permafrost in the field are closely related to local factors such as topography, geomorphology, groundwater, and lithology of shallow ground. It is believed that the formation of the island talik in the study area is controlled by solar radiation and precipitation infiltration.

Owing to the limitations of the apparatus, the influence of its principal stress direction on the anisotropic behavior and non-coaxiality of frozen soil has not been fully considered in previous studies. At a temperature of -10°C, a series of hollow cylinder tests for frozen standard sand (FSS) was conducted under different directional angles of major principal stress and mean principal stresses in this study. The experimental results indicate that the stress-strain-strength anisotropy and non-coaxiality of the FSS are highly dependent on the principal stress direction. The stress components of the FSS vary linearly with increasing shear stress at different directional angles of the major principal stress and mean principal stresses. With a linear increase in shear stress, the strain components of the FSS exhibited a nonlinear increasing trend. The FSS strength gradually decreased as the directional angle of the major principal stress and the mean principal stresses in the test range increased. Under the different principal stress directions, the non-coaxiality of the FSS, non-coincidence of the direction of the principal strain increment and the principal stress direction, were observed. The directions of the principal strain increment and principal stress gradually tended to be coaxial as shear stress increased. Although the non-coaxial angle of the FSS increased gradually with an increase in the directional angles of the major principal stress, it did not change with the change in the mean principal stress. The non-coaxial angle of the FSS was observed to be as large as 35° in the early stage of shearing under different mean principal stresses.

Changes of the lakes on high-altitude regions of the Tibet Plateau influence the state of the surrounding permafrost. Due to the climate warming and wetting trend, extreme events including lake outburst has occurred more frequent. In 2011, an outburst event occurred on the Zonag Lake and this event changed the water distribution in the basin, leading a rapid expansion of the Tailwater lake, named as the Salt Lake. However, the construction of the drainage channel in the Salt Lake ended the expansion process and the shrinkage of the lake started since 2020. To investigate the permafrost state around the Salt Lake, multiple methods, including drilling boreholes, the unmanned aerial vehicle survey and the ground penetrating radar detection have been applied. By integrating these multi-source data, the thermal regime, topography and the spatial distribution of the permafrost around the Salt Lake were analyzed. The result showed that the permafrost state around the Salt Lake was related to the distance from the lake water. The permafrost table appears at 90 m away from the Salt Lake and interrupted by a nearby thermokarst lake at 220 m. The ground temperature in the natural field is 0.2 °C lower than the temperature in the lake at a depth of −5 m.

Using the triaxial shear or compressive strength as a single index of the resistance of frozen soils to failure does not always meet frozen soil engineering requirements for the comprehensive evaluation of the resistance. In this study, triaxial compression experiments were carried out on undisturbed ice-rich frozen clay samples with various levels of water content under different confining pressures to study the characteristics of the failure strain energy density of the samples. The results indicate that as the confining pressure increased, the failure strain energy density first increased and then decreased. The failure strain energy density reached a maximum at a critical confining pressure of 2.00 MPa for 13.25–25.76% water content and 1.00 MPa for 26.02–45.82% water content. The failure strain energy density increased as the water content increased at low confining pressures (0.05–0.50 MPa) but then declined slightly at intermediate confining pressures (1.00–2.00 MPa). At a high confined pressure of 3.00 MPa, the failure strain energy density decreased overall as the water content increased. There were similarities and differences between the change characteristics of the compressive strength and the failure strain energy density. The failure strain energy density can be used as a supplementary reference index of the resistance of frozen soils to damage. The variation characteristics of the failure strain energy density of undisturbed frozen clay are essentially consistent with those of remolded frozen sandy soils. However, there are also clear differences between the characteristics of the failure strain energy density of these two types of frozen soil.

As a major parameter in the energy balance of the ground surface, temperature represents the level of exchange of energy and moisture between the ground and air. The Qinghai-Tibet Plateau (QTP) has the permafrost region with the highest altitude and the largest area in low–middle latitude of the world. The variation in ground surface temperature has an impact on the existence and development of the permafrost. Therefore, the analysis of the ground surface temperature in the QTP is significant to reflect the energy exchange in permafrost regions. This paper collected solar radiation data and calculated the conversion coefficient from total solar radiation to long-wave radiation of the ground surface on different underlying surfaces. The ground surface temperature was inversely calculated and modified based on the reception of solar radiation on different underlying surfaces. A simplified calculation model of ground surface temperature was built to reflect the ground surface temperature on different underlying surfaces of the QTP. The calculation results were compared with MODIS and showed good fitness, providing a systematic and reliable method for calculating the ground surface temperature on the QTP. The above model plays a significant role in the estimation of soil moisture, ground surface energy and water balance.

The shear behaviors of concrete-frozen soil interface are important for analyzing the performance of engineering structures buried in the frozen ground. In this paper, a series of direct shear tests were carried out to determine the concrete-soil interface behaviors at different test temperatures (19°C, −1°C, −3°C, and −5°C) and initial water contents (9.2%, 13.1%, 17.1%, and 20.8%) of soils. The interface shear behaviors, including the shear stress versus horizontal displacement, interface cohesion, and interface friction coefficient, were analyzed based on the test results. Then, a simple, nonlinear model was proposed and verified for the interface shear behaviors. The results show that the effect of initial water content and test temperature on the interface shear behavior is significant, and the peak stress increases with the increasing initial water content and decreasing test temperature. The interface cohesion is sensitive to the test temperature and initial water content, while the interface friction coefficient is insensitive to both the factors. The parameters of the simple nonlinear model can be gained by back-analyzing the test results. The predictions made by the proposed model are found to be in good agreement with the experimental results.

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.

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.

The lakes distributed in permafrost areas on the Tibetan Plateau (TP) have been experiencing significant changes during the past few decades as a result of the climate warming and regional wetting. In September 2011, an outburst occurred on an endorheic lake (Zonag Lake) in the interior of the TP, which caused the spatial expansion of three downstream lakes (Kusai Lake, Haidingnor Lake and Salt Lake) and modified the four independent lake catchments to one basin. In this study, we investigate the changes in surficial areas and water volumes of the outburst lake and related downstream water bodies 10 years after the outburst. Based on the meteorological and satellite data, the reasons for the expansion of downstream lakes were analyzed. Additionally, the importance of the permafrost layer in determining hydrological process on the TP and the influence of from lake expansion on engineering infrastructures were discussed. The results in this study showed the downstream lakes increased both in area and volume after the outburst of the headwater. Meanwhile, we hope to provide a reference about surface water changes and permafrost degradation for the management of lake overflow and flood on the TP in the background of climate warming and wetting.

Most red beds demonstrate inferior geotechnical properties in natural conditions and need to be improved when used as construction material. In this study, a serious of triaxial tests, permeability tests, and scanning electron microscopy (SEM) analysis were carried out on lime-stabilized and untreated red bed soil after experiencing different wetting-drying (W-D) cycles. The test results showed that, with the increase in the added lime, the shear strength, strength parameters (including the cohesion and the internal friction angle), and the shear modulus of red bed soil increased gradually. For the untreated specimens, the four parameters decreased considerably after experiencing W-D cycles, while for the lime-stabilized specimens, they generally increased with an increase in the W-D cycles. Without experiencing the W-D cycles, the permeability coefficient increased by two times after it was stabilized with 10% lime. But with an increase in the W-D cycles, the permeability coefficient of the untreated and lime-stabilized specimens continuously increased and significantly decreased, respectively. Finally, variations in microstructure of the red bed soil under the effects of the lime stabilization and W-D cycles were discussed based on the SEM analysis. The results may contribute to improvement of red bed soil when used as roadbed and airfield fillings.

The Loess Plateau is one of the most tectonically and seismically active areas in the world. Observations from past strong earthquakes, particularly the Minxian–Zhangxian and Wenchuan earthquakes, have shown distinctive evidence of seismic site effects in the mountainous area of southeastern Gansu province. In this study, seismic damage in the loess areas of southeastern Gansu province induced by these earthquakes was investigated and briefly described. Different types of ground motion were selected, and the one-dimensional equivalent linear method was used for numerical analysis of the ground motion effects in the loess regions. Moreover, seismic response analysis of a typical loess tableland was conducted. The results showed that the seismic responses of a typical loess tableland under different seismic excitations have totally different dynamic characteristics. Moreover, the seismic damage in loess regions was more serious under far-field seismic excitation compared with near-field seismic excitation with the same peak acceleration. Through this study, the quantitative assessment of ground motion effects can be approximately estimated and the mechanism of site amplification effects on ground motion is further explained.

A series of laboratory experiments, including oedometer tests, direct shear tests, and mercury intrusion porosity (MIP) tests, were conducted to investigate the effects of repeated wetting-drying-freezing-thawing (WDFT) cycles on the mechanic behaviors and pore characteristics of compacted loess. The results of mechanical tests indicate that the WDFT weathering can cause significant deterioration of mechanical properties for compacted loess. As the number of treatment cycles increases, vertical compression strain and coefficient of collapsibility of the loess specimens increase while the cohesion decreases. The compacted and noncollapsible loess specimen exhibits collapse again after the 7 WDFT cycles. The results of MIP tests show that WDFT cycles have a main influence on the pores with a pore diameter of 1∼35 μm between the soil aggregates, and medium pore contents (10∼35 μm) increase significantly with the increasing number of WDFT cycles. By comparing compression and collapse characteristics of the loess specimens subjected to wetting-drying, freeze-thaw, and WDFT cycles, we found that the dry-wet action plays the dominant role in the deterioration of engineering properties of compacted loess during WDFT cycles.

Mechanical control of drifting sand used to protect the Qinghai–Tibet Railway from sand damage inevitably results in sand deposition, and the change in radiation and heat flux after the ground surface is covered with sandy sediments remains unclear. These variations were studied in this work through field observations along with laboratory analyses and tests. After the ground surface was covered with sandy sediments produced by the mechanical control of sand in the Qinghai–Tibet Railway, the reflectivity increased, and the annual average reflectivity on the surface covered with sandy sediments was higher than that without sandy sediments, with the value increasing by 0.043. Moreover, the surface shortwave radiation increased, whereas the surface net radiation decreased. The annual average value of the surface shortwave radiant flux density on the sandy sediments was higher than that without sandy sediments, with the value increasing by 7.291 W·m−2. The annual average value of the surface net radiant flux density on the sandy sediments decreased by 9.639 W·m−2 compared with that without sandy sediments. The soil heat flux also decreased, and the annual average value of the heat flux in the sandy sediments decreased by 0.375 W·m−2 compared with that without sandy sediments. These variations caused the heat source on the surface of sandy sediments underground to decrease, which is beneficial for preventing permafrost from degradation in the section of sand control of the railway. Keywords: Mechanical control of sand, Sand depositions, Surface radiation, Heat flux, Qinghai–Tibet Railway

A series of triaxial compression tests, which has capable of measuring the volumetric strain of the sample, were conducted on columnar ice. A new testing approach of probing the experimental yield surface was performed from a single sample in order to investigate yield and hardening behaviors of the columnar ice under complex stress states. Based on the characteristic of the volumetric strain, a new method of defined the multiaxial yield strengths of the columnar ice is proposed. The experimental yield surface remains elliptical shape in the stress space of effective stress versus mean stress. The effect of temperature, loading rate and loading path in the initial yield surface and deformation properties of the columnar ice were also studied. Subsequent yield surfaces of the columnar ice have been explored by using uniaxial and hydrostatic paths. The evolution of the subsequent yield surface exhibits significant path-dependent characteristics. The multiaxial hardening law of the columnar ice was established experimentally. A phenomenological yield criterion was presented for multiaxial yield and hardening behaviors of the columnar ice. The comparisons between the theoretical and measured results indicate that this current model is capable of giving a reasonable prediction for the multiaxial yield and post-yield properties of the columnar ice subjected to different temperature, loading rate and path conditions. Keywords: Columnar ice, Multiaxial loading, Hardening rule, Path dependency, Yield criterion

The China–Russia crude oil pipeline (CRCOP) traverses rivers, forests, and mountains over permafrost regions in northeastern China. Water accumulates beside the pipe embankment, which disturbs the hydrothermal balance of permafrost underlying the pipeline. Ground surface flows along the pipeline erode the pipe embankment, which threatens the CRCOP’s operational safety. Additionally, frost heave and thaw settlement can induce differential deformation of the pipes. Therefore, it is necessary to acquire the spatial distribution of water features along the CRCOP, and analyze the various hazard probabilities and their controlling factors. In this paper, information regarding the permafrost type, buried depth of the pipe, soil type, landforms, and vegetation were collected along the CRCOP every 2 km. Ponding and erosive damage caused by surface flows were measured via field investigations and remote sensing images. Two hundred and sixty-four pond sites were extracted from Landsat 8 images, in which the areas of 46.8% of the ponds were larger than 500 m2. Several influential factors related to freeze–thaw hazards and erosive damage were selected and put into a logistic regression model to determine their corresponding risk probabilities. The results reflected the distributions, and forecasted the occurrences, of freeze–thaw hazards and erosive damage. The sections of pipe with the highest risks of freeze–thaw and erosive damage accounted for 2.4% and 6.7%, respectively, of the pipeline. Permafrost type and the position where runoff encounters the pipeline were the dominant influences on the freeze–thaw hazards, while the runoff–pipe position, buried depth of the pipe, and landform types played a dominant role in erosive damage along the CRCOP. Combined with the geographic information system (GIS), field surveys, image interpretation and model calculations are effective methods for assessing the various hazards along the CRCOP in permafrost regions.

The damage variable is very important to study damage evolution of material. Taking frozen loess as an example, a series of triaxial compression and triaxial loading-unloading tests are performed under five strain rates of 5.0 × 10−6–1.3 × 10−2/s at a temperature of −6°C. A damage criterion of frozen loess is defined and a damage factor Dc is introduced to satisfy the requirements of the engineering application. The damage variable of frozen loess is investigated using the following four methods: the stiffness degradation method, the deformation increase method, the dissipated energy increase method, and the constitutive model deducing method during deformation process. In addition, the advantages and disadvantages of the four methods are discussed when they are used for frozen loess material. According to the discussion, the plastic strain may be the most appropriate variable to characterize the damage evolution of frozen loess during the deformation process based on the material properties and the nature of the material service.

Most previous studies of the Qinghai-Tibet engineering corridor (QTEC) have focused on the impacts of climate change on thaw-induced slope failures, whereas few have considered freeze-induced slope failures. Terrestrial laser scanning was used in combination with global navigation satellite systems to monitor three-dimensional surface changes between 2014 and 2015 on the slope of permafrost in the QTEC, which experienced two thawing periods and a freezing period. Soil temperature and moisture sensors were also deployed at 11 depths to reveal the hydrological–thermal dynamics of the active layer. We analyzed scanned surface changes in the slope based on comparisons of multi-temporal point cloud data to determine how the hydrological–thermal process affected active layer deformation during freeze–thaw cycles, thereby comprehensively quantifying the surface deformation. During the two thawing periods, the major structure of the slope exhibited subsidence trends, whereas the major structure of the slope had an uplift trend in the freezing period. The seasonal subsidence trend was caused by thaw settlement and the seasonal uplift trend was probably due to frost heaving. This occurred mainly because the active layer and the upper permafrost underwent a phase transition due to heat transfer. The ground movements occurred approximately in the soil temperature conduction direction between the top of the soil and the permafrost table. The elevation deformation range was mainly −0.20 m to 0.20 m. Surface volume increases with heaving after freezing could have compensated for the loss of thawing twice and still led to the upward swelling of the slope. Thus, this type of slope in permafrost is dominated by frost heave. Deformation characteristics of the slope will support enhanced decision making regarding the implementation of remote sensing and hydrological–thermal measurement technologies to monitor changes in the slopes in permafrost adjacent to engineering corridors, thereby improving the understanding and assessment of hazards.

As a unique hydro-geological phenomenon in permafrost regions, the seepage of supra-permafrost groundwater will carry a large amount of heat and cause differential settlement in the embankment. This paper presents the results of a field study monitoring the supra-permafrost groundwater levels on both sides of an embankment in permafrost regions. It describes a two-dimensional coupled hydro-thermal model and uses it to analyze the influence of seepage on its temperature field considering climate warming. The results show that seepage exacerbates permafrost thawing and thickens the active layer. The thermal influence on the sunny side of the embankment toe is more significant than that on the shady side, which will cause differential settlement in the embankment. After 50 years of operation, the embankment soil temperature with seepage during freezing is 0.2 (C warmer than that without seepage, and the thermal influence diminished with the increase in depth. Additionally, seepage influences the thermal regime in vertical and horizontal directions of the embankment. During freezing seasons, the thaw depth increases, and the horizontal thaw range decreases. During thawing seasons, the thaw range grows both vertically and horizontally. [ABSTRACT FROM AUTHOR]