The measurement of pile axial load is of great significance to determining pile foundation design parameters such as skin friction and end bearing capacity and analyzing load transfer mechanisms. Affected by the temperature and ice content of frozen ground, the interface contact relationship between pile foundation and frozen soil is complicated, making pile axial load measurements more uncertain than that in non-frozen ground. Therefore, it is necessary to gain an in-depth understanding of the current pile axial load test methods. Four methods are systematically reviewed: vibrating wire sensors, strain gauges, sliding micrometers, and optical fiber strain sensors. At the same time, the applicability of the four test methods in frozen soil regions is discussed in detail. The first two methods are mature and commonly used. The sliding micrometer is only suitable for short-term measurement. While the Fiber Bragg grating (FBG) strain gauge meets the monitoring requirements, the Brillouin optical time-domain reflectometer (BOTDR) needs further verification. This paper aims to provide a technical reference for selecting and applying different methods in the pile axial load test for the stability study and bearing capacity assessment of pile foundations in cold regions.

As a linkage between plants and soil, litter decomposition and its effect on nutrient recirculation have an important ecological significance as they contribute to soil structure improvement and the restoration of degraded ecosystems. Fragile ecosystems in arid regions (both hot and cold) are depleted in soil organic matter, and as a result of various factors their circulation of material and energy is slower. Here we discuss how litter decomposition is necessary to maintain the stability of fragile ecosystems. We reviewed research on litter decomposition carried out in arid regions. Our objective in this review is to outline how litter decomposition, and the subsequent buildup of organic matter in soil, is a key process determining the stability of fragile ecosystems. Our review shows that existing studies have focused on the influence of single ecological factors on litter decomposition and nutrient cycling, and highlights how the exploration of interactions among factors determining litter decomposition is still lacking. This interaction is a key aspect, since in the real world, decomposition and nutrient return to soil of litter products is affected by multiple factors. We propose a network setup on a cross-regional scale using standardized methods (e.g., the tea bag method) to understand litter decomposition and nutrient return in fragile ecosystems. Such a unique network could contribute to establish predictive models suitable for litter decomposition and nutrient return in these areas, and thus could provide theoretical and practical support for regional ecological protection and high-quality development.

Timely removal of the flower is a key agricultural measure to ensure the concentrated supply of nutrients for the growth of underground bulbs and to increase the yield of lilies. Removing flowers and returning them to the field is one of the traditional ways of treatment, and field litter is formed at this time. Previous study showed that the decomposition of litter changes the soil properties. In order to study the effects of lily litter decomposition on soil physical and chemical properties and microbial structure, three treatments were set up in reference to the Decomposition Bag Method: control (CK), Lanzhou lily flower treatment (LZF), and Zhongbai No.1 flower treatment (ZBF). The effects of lily decomposition on soil physical and chemical properties and microbial community composition were studied in order to provide a scientific basis and theoretical guidance for the planting process of Lanzhou lily. The results show that the decomposition of lily flowers significantly increased the contents of soil organic matter, soil total nitrogen, soil total phosphorus and soil available potassium, and decreased soil pH. RDA shows that soil available nutrients and pH were the driving factors for the change of the soil microbial community. A short-term change of soil microenvironment caused by the decomposed lily flower is beneficial to growing the Lanzhou lily. However, under the correlation analysis of environmental factors, the long-term effects of returning the Lanzhou lily flower to the field, such as the trend of soil acidification, need to be further studied.

Based on the engineering background of the contact channel between Shangyang and Gushan of Fuzhou Metro Line 2 undercrossing the existing tunnel line, the freezing temperature field of the contact channel, the displacement field of the existing tunnel line and the contact channel with different net distances and horizontal angles are analyzed by ANSYS finite element software and field measurement method. The obtained results indicate that during the freezing period, the temperature drops at different measuring holes are almost the same. The temperature near the bottom freezing tube drops faster than that far from the tube. It is found that the bilateral freezing technique improves the formation of the freezing wall in the intersection area. In this case, the intersection time of the cross-section is 7 days faster than that of the adjacent ordinary section. The change curve of the displacement of the surface uplift in different freezing periods with the distance from the center of the channel is "M" shaped. The maximum uplift displacement at 12 m from channel center is 25 mm. The vertical displacement of the measuring point located above the central axis of the connecting channel is large. The farther the point from the central axis, the smaller the corresponding vertical displacement. When the horizontal angle between the existing tunnel and the connecting channel is less than 60°, the existing vertical displacement of the tunnel changes rapidly with the horizontal angle, reaching 0.17 mm/°. Meanwhile, when the net distance is less than 6.1 m, the change rate of the vertical displacement of the tunnel is up to 2.4 mm/m.

It is feasible to study the mechanical characteristics of coarse-grained soil by simulated granular materials such as glass beads. In this paper, 3 mm diameter glass beads are used to conduct drained and undrained triaxial tests under the condition of different confining pressures to explore their strength, deformation and critical state characteristics. Specifically, the influence of drainage and confining pressure on the stick-slip phenomenon of glass beads is reported. The experimental findings from triaxial tests show that the stress-strain relationship of glass beads softens when the confining pressure is high. Under the undrained condition, the initial modulus increases with the increase in the confining pressure. In contrast, it is not significantly affected by the confining pressure under the drained condition. It is quite evident that the glass beads hardly contract during the shearing process, and their stress path is approximately a segmented straight line. The slope of the critical state line under the undrained condition is greater than that under the drained condition, and the friction angle of the glass beads under the undrained and drained conditions is calculated to be 28.1° and 29.5°, respectively. The phenomenon of stick-slip has been depicted for the different test conditions, and the stick-slip amplitude linearly increases with the confining pressure, especially in the undrained condition. It is also found that the maximum energy released from the phenomenon of stick-slip increases linearly with the confining pressure.

This paper investigates the influence of the deviation in freeze pipe installation on the development of the frozen wall in long cross passages by numerical simulation with ANSYS software. The study case is from the artificial ground freezing project along the Fuzhou Metro Line 2 between Ziyang Station and Wuliting Station. Two freeze-pipe configurations, i.e., one with perfectly aligned pipes without any deviation from design and another with randomly distributed deviation, are included for comparison. The effect of the random deviation in the freeze pipes on frozen wall interconnection time, the thickness of the frozen wall and the development of the temperature field is explored. For the characteristic section of the numerical model at a depth of 25 m, it is found that the frozen wall interconnection time under the random deviation case and no deviation case is 24 days and 18 days, respectively. The difference in the thickness of the thinnest frozen wall segment between the random deviation and no deviation cases is the largest in the early freezing stage (up to 0.75 m), which decreases with time to 0.31 m in the late freezing stage. The effects of random deviation are more significant in the early freezing stage and diminish as the freezing time increases.

The Freeze-Sealing Pipe-Roof (FSPR) method, which has been applied for the first time in the Gongbei Tunnel of the Hong Kong-Zhuhai-Macao Bridge, is a new approach of tunnel pre-support that allows flexible adjustment of freeze tube arrangement and can be adapted to different environmental conditions. When the FSPR method is used to construct shallow burial submerged tunnels, the frozen wall to hold back groundwater during excavation will be weakened by air and water flows inside and outside the tunnel, and its waterproof performance needs to be further investigated. In this paper, a two-dimensional numerical model of the temperature field considering excavation and moving water boundary is established based on the preliminary design scheme and in-situ conditions and is used to analyze the variation in frozen curtain properties with various active freezing times during excavation. The results show that excavation has a weakening effect on both sides of the frozen wall, with a greater effect on the inner side, and a positive temperature appears in the local area inside the jacked pipe. The concrete fill in the jacked pipe obviously improves the freezing efficiency, and the tunnel excavation after 60 days of active freezing in the interval filling mode can ensure that the frozen soil thickness at the thinnest segment exceeds 2 m, i.e., the design requirement. In practice, the active freezing time can be extended appropriately to reduce the influence of river water flow above the tunnel. The study serves as a technical reference for the design and implementation of similar projects.

Damage caused by frost heave leads to costly maintenance in cold regions, like Hokkaido, Japan. Therefore, the study of the frost mechanism with experimental and numerical methods has been of great interest. Numerous models have been developed to describe the freezing process of saturated soil, which differs from the partially saturated conditions in the field. In fact, most subsurface soils are unsaturated. The freezing process of partially saturated soils is more complex than saturated soils, as the governing equations show strongly nonlinear characteristics. This study proposes a thermo-hydro-mechanical coupled model considering the heat transfer, water infiltration, and deformation of partially saturated soil to reproduce the freezing process of partially saturated frost susceptible soils distributed in Hokkaido. This model better considers the water-ice phase change and soil freezing characteristic curve (SFCC) during freezing under field conditions. The results from the multiphysics simulations agree well with the frost heave and water migration data from frost heave tests of Touryo soil and Fujinomori soil. In addition, this study discussed the influence of the various factors on frost heave amount, including temperature gradients, overburden pressures, water supply conditions, cooling rates, and initial saturation. The simulation results indicate that the frost heave ratio is proportional to the initial degree of saturation and is inversely proportional to the cooling rate and overburden pressure.

Moreover, simulation under the open system generates much more frost heave than under the closed system. Finally, the main features of the proposed model are revealed by simulating a closed-system frost heave test. The simulation results indicate that the proposed model adequately captures the coupling characteristics of water and ice redistribution, temperature development, hydraulic conductivity, and suction in the freezing process. Together with the decreased hydraulic conductivity, the increased suction controls the water flow in the freezing zone. The inflow water driven by cryogenic suction gradient feeds the ice formation, leads to a rapid increase in total water content, expanding the voids that exceed the initial porosity and contributing to the frost heave.

CO₂ released by soil serves as an important link between terrestrial ecosystems and atmospheric CO₂, whose small changes may significantly affect the global carbon cycle. In order to reveal the spatio-temporal variations of CO₂ concentrations in deep loess, this paper takes Qingliangsi Gully watershed in northwestern Shanxi Province, China as an example to systematically study soil CO₂ concentration and its spatio-temporal variations and carbon sink significance under different watershed locations and different land use types. Results show that: (1) The release potential of the loess soil is larger in the depth range of 2 m, which is much more likely to be the CO₂ release area. (2) Grassland and forest are more advantageous in terms of soil microbial activity and soil carbon reserve compared with farmland. In addition, the change of land use type from farmland to grassland can increase soil organic carbon reserve, which is of far-reaching significance to the global carbon cycle. This is especially true in an area like the Loess Plateau with densely covered hills, gullies, and serious soil erosion in an area of 64×10⁴ km². (3) In the study area, the diurnal concentration of soil CO₂ at different depths shows a weak "high-low-high-low" trend from 08:00 to 07:00 next day; and in deep soil it has a lag time compared with the daily change of temperature, generally about 4-12 h, which may be caused largely by the more compact loess structure. It is worth pointing out that the Loess Plateau in China, with a thickness of the loess of tens to hundreds of meters, has the most abundant soil resources in the world, and also stores a large amount of terrestrial soil carbon, which carries the hope of promoting the research of global carbon cycle.

High temperature rutting is a typical highway damage in Xinjiang, China, and its trigger process usually has a close relationship with characteristics of road temperature distribution. A numerical model of earth-atmosphere coupling heat transfer on a typical section of the Beijing-Xinjiang Expressway (G7) from Wutong Daquan to Yiwu was established in this work. Spatiotemporal characteristics of pavement structure layer temperature distribution, frequency and duration times of road surface high temperature from May 1 to September 30 are statistically studied. The effects of wind speed, weather and air temperature on asphalt layer and pavement temperature are analyzed. The results show that: (1) Spatial and temporal temperature distribution characteristics of pavement structural layers are greatly affected by the coupled earth-atmosphere heat transfer process. Surface temperature increases along the airflow direction and daily temperature variation of the pavement structure layer decreases with an increase of depth. (2) G7 expressway will face the challenge of high rutting damage. The proportion of temperature higher than 50 °C for pavement surface and asphalt upper layer both exceeds 50% and high temperature of road lasts for more than six hours in numerous days. (3) High temperatures of asphalt pavement are usually associated with low ambient wind speeds, while the wind flow has little cooling effect when the road surface temperature is relative high. Weather conditions have a significant impact on temperature of the road surface. The probability of high temperature in sunny days is obviously higher than other weather conditions. (4) Pavement temperature rises as air temperature rises. When air temperature is higher than 30 °C, the proportion of pavement daily maximum temperature over softening point reaches up to 78%.

Portable in-situ devices have been used for characterizing low accessible field, such as the railway subgrade. In this study, the automated cone penetrometer (ACP) was designed for the application on the railway subgrade. ACP is composed of the cone tip, driving rod, and hydraulic hammer system. The hydraulic motor lifts and drops the 294.3 N hammer from a height of 200 mm such that the potential energy of 58.9 N?m impacts the driving rod. The N-value (N_ACP) from the ACP test was compared with the dynamic cone penetration index (DCPI) from the dynamic cone penetrometer (DCP) test. The test results show that the N_ACP and DCPI profiles show opposite trend owing to the inverse concept of the unit. From the correlation of DCPI and N_ACP, the limitation of DCPI reveals owing the minimum manually measured value of 1 mm/blow. Additionally, the evaluation of the deflection modulus (E_FWD) using N_ACP is more efficient than that using DCPI. Based on the result of this study, we suggest that ACP can be used for strength and stiffness evaluation of railway subgrade rapidly and reliably.

In order to study the mechanical properties and energy evolution of low-temperature concrete during uniaxial compression, a uniaxial compression test was performed on concrete. In addition, the evolution laws of compressive strength, deformation modulus and total energy, elastic potential energy, dissipated energy and peak energy of concrete in the process of deformation and failure are analyzed. The effects of age and temperature on low-temperature concrete is analyzed from the perspective of energy. Test results show that temperature improves the strength and deformation of concrete to varying degrees. When cured for 28 days, the compressive strength and deformation modulus of concrete at -20 ℃ is increased by 17.98% and 21.45% respectively, compared with the compressive strength and deformation modulus at room temperature of 20 ℃. At the point of failure of the concrete under uniaxial compression, the total damage energy and the dissipation energy both increase, while the developed elastic strain energy increases and then decreases. Increase in curing duration tends to increase the total destruction energy of concrete, peak point elastic strain energy, peak point dissipation energy, and peak point total energy. Whereas increase in curing durations, has shown to decrease the total destruction energy of concrete, the peak point elastic strain energy, peak point dissipation energy, and peak point total energy. The peak point strain energy reflects the ability of low-temperature concrete to reasonably resist damage. By using the principle of energy analysis to study the deformation process of concrete, it provides research methods and ideas for the deformation analysis of this type of material under load.

Bacteria constitute a large proportion of the biodiversity in soils and control many important processes in terrestrial ecosystems. However, our understanding of the interactions between soil bacteria and environmental factors remains limited, especially in sensitive and fragile ecosystems. In this study, geographic patterns of bacterial diversity across four sandy grasslands along a 1,600 km north-south transect in northern China were characterized by high-throughput 16S rRNA gene sequencing. Then, we analyzed the driving factors behind the patterns in bacterial diversity. The results show that of the 21 phyla detected, the most abundant were Proteobacteria, Actinobacteria, Acidobacteria and Firmicutes (average relative abundance >5%). Soil bacterial operational taxonomic unit (OTU) numbers (richness) and Faith's phylogenetic diversity (diversity) were highest in the Otindag Sandy Land and lowest in the Mu Us Sandy Land. Soil electrical conductivity (EC) was the most influential factor driving bacterial richness and diversity. The bacterial communities differed significantly among the four sandy grasslands, and the bacterial community structure was significantly affected by environmental factors and geographic distance. Of the environmental variables examined, climatic factors (mean annual temperature and precipitation) and edaphic properties (pH and EC) explained the highest proportion of the variation in bacterial community structure. Biotic factors such as plant species richness and aboveground biomass exhibited weak but significant associations with bacterial richness and diversity. Our findings revealed the important role of climate and salinity factors in controlling bacterial richness and diversity; understanding these roles is critical for predicting the impacts of climate change and promoting sustainable management strategies for ecosystem services in these sandy lands.