Cold Regions Science and Technology最新文献

Generally, artificial ground freezing (AGF) technology is utilized to guarantee tunnel safety during construction. However, the soil structure changes significantly after freeze-thaw, resulting in uneven deformation of the tunnel under traffic loading from subway vibration. To solve this problem effectively, it is necessary to consider the combined impact of freeze-thaw, salt, and traffic loading damage that marine soft soil must withstand simultaneously. For this reason, cyclic triaxial test and NMR test were performed on the silty clay saturated with NaCl solution in this study. The influence of three main factors on dynamic properties has been thoroughly investigated, namely freeze-thaw, salt content, and confining pressure. According to cyclic triaxial test, the shape of the hysteresis loop of the specimens after freeze-thaw changed more significantly with increasing loading cycles. The dynamic elastic modulus was weakened by freeze-thaw, while improved by the addition of NaCl. Damping ratio was consistent with the dynamic elastic modulus law. It was worth noting that the different freezing temperatures (−10 °C, −20 °C and − 30 °C) had only a slight impact on dynamic elastic modulus, as well as damping ratio. Mathematical models were proposed to forecast the dynamic elastic modulus and damping ratio regarding marine soft clay. NMR test indicated that the addition of salt made the internal pore environment of the specimens tend to be consistent and enhanced the water-solid interaction. The increase in porosity resulted in the decrease in dynamic elastic modulus. The results have provided valuable insights into the mechanical characteristics of marine soft clay when AGF technology is applied.

Soil moisture freezing in cold climates leads to frost heave, a phenomenon influenced by soil texture, temperature, moisture levels, and applied loads. This investigation explores frost heave characteristics of subgrade soil under traffic-induced cyclic stresses, including cyclic compressive stress and alternating horizontal cyclic shear stress. A new frost heave test system was developed, featuring advanced temperature control and accurate loading path reproduction. Comprehensive frost heave experiments were performed to examine the frost heave process under various cyclic stress circumstances. Results indicate that cyclic stresses intensify in-situ frost heave of soil, with horizontal cyclic shear stress having a more significant promoting effect than vertical cyclic stress. The combination of vertical cyclic stress and horizontal cyclic shear stress leads to an increase in segregated frost heave. Moreover, vertical cyclic stress amplifies water absorption during soil frost heave. Total vertical deformation encompasses frost deformation in the frozen zone and consolidation in the unfrozen zone. Vertical cyclic stress may inhibit segregated ice lens formation and encourage consolidation in the unfrozen zone, thereby impeding vertical deformation. The simultaneous application of vertical cyclic stress and horizontal cyclic shear stress results in more intense ice segregation and moisture accumulation near the stable frost front.

The density of linear engineering projects within the Qinghai-Tibet Engineering Corridor has increased, and the study of the thermal influence range of a single linear engineering project has become more important. This paper employs the finite difference method to investigate the influence of embankment size, mean annual ground temperature (MAGT), and construction time on the spatial-temporal evolution of the embankment's lateral and vertical thermal influence range. Additionally, a parameter sensitivity analysis of the lateral and vertical thermal influence ranges throughout the entire service life of the embankment is conducted. The results indicate that under the same service time, the lateral-vertical ratio (L_c/D), as well as the lateral thermal influence range (L_c) and the vertical thermal influence range (D), increase linearly with increasing embankment height and pavement width. The L_c/D increases with increasing MAGT, but the L_c and D decrease with increasing MAGT. The L_c/D, the L_c, and the D are not significantly affected by construction time. During the 50-year service life of the embankment, the most significant factor impacting the L_c is the pavement width, and the MAGT is the most significant factor impacting the D. The results are expected to serve as a guide for the design and construction of roads in the permafrost regions of the Qinghai-Tibet Plateau.

Aiming at the obvious salt-frost heave disease of loess-like sulphate soil in seasonal frozen areas, the compaction characteristics, salt-frost heave property and improvement effect of saline soil treated by adding lime, silica fume and lime-silica fume mixture are investigated. The results show that the salt-frost heave and collapse occur alternately and periodically with the freeze-thaw process. In addition, the peak salt-frost heave and thawing residual salt-frost heave increases with the increasing salt content, and the salt-frost heave shows obvious linear accumulation. The composition and dosage of the curing agent, freeze-thaw times and maintenance time have a significant influence on the improvement effect of salt-frost heave. The improvement effect of the lime-silica fume mixture far exceeds that of lime or silica fume alone. Moreover, repeated freeze-thaw cycles have a significant deteriorating effect on reducing salt-frost heave, and the salt-frost heave decreases with increasing maintenance time. The mechanism of curing saline soil by lime-silica fume mixture mainly includes physical filling effect and pozzolanic reaction effect. In particular, the strong pozzolanic reaction between lime and silica fume produces cementing material (CSH), effectively cementing the soil particles and substantially inhibiting the salt-frost heave.

The prevention of ice/frosting formation is crucial in cold region for various applications. Superhydrophobic coatings are known for their excellent anti-icing/anti-frosting properties. In this study, a durable superhydrophobic PTFE coating on a stainless steel surface was fabricated with a high water contact angle of 171.4° and a low rolling angle of 1.1°. The freezing of water droplets on the coating exhibits a significantly prolonged duration of 809 s at −10 °C, representing a 25-fold increase compared to the uncoated stainless steel surface. The ice adhesion strength is reduced by 83.7%, making ice easier to remove. Anti-frosting tests show that a thinner and lower-density layer of frost formed on the PTFE coating due to its micro-nano hierarchical structure. Furthermore, the superhydrophobic PTFE coating demonstrates excellent mechanical stability, droplet bouncing dynamics and self-cleaning properties. It is anticipated that this durable superhydrophobic PTFE coating will be a candidate for anti-icing/anti-frosting and self-cleaning applications

In this study, we focused on essential parameters derived from the deep foundation pit project of a metro station located in Northeast China. We analyzed the monitoring data pertaining to critical indicators, including the prestressing anchor cable tension, horizontal displacements of pile tops, and deformation displacements of anti-slide piles. A three-dimensional finite element model of a prestressed anchorage system was developed. To assess the reliability of the model, simulations of the system's performance were conducted, with comparisons of the results with field monitoring observations. On this basis, the support performance of the prestressed anchorage system during the overwintering period was investigated. The impacts of key variables, such as prestressing, vertical spacing, anchoring angle, and anchorage length of the anchor cable, on its protective performance were evaluated. Specifically, the impact of these parameters on performance indicators, including the horizontal displacement, internal force within the pile body, and overall stability factor of the pit were assessed. Furthermore, the distribution patterns and trends of these performance indicators under various working conditions were compared and analyzed. Finally, the optimal support strategy was pinpointed utilizing a multifactorial orthogonal test. This study provides valuable insights for simulating and designing prestressed anchorage systems for foundation pits in overwintering conditions, serving as a valuable reference for future pile anchor system construction and design in areas subjected to freeze-thaw cycles.

Ice nucleation active (INA) bacteria are capable of triggering ice formation close to 0 °C, but their ability of increasing ice content in warm permafrost remain unknown. Ice content is vital because it determines the bearing capacity of warm permafrost. Through nuclear magnet resonance and direct shear device, we found that adding INA bacterium Pseudomonas syringae with a concentration of 1 g/L in warm frozen soil can result in 64% increase in the shear strength, 113% increase in cohesion and 27% increase in ice content. The internal friction angle of warm frozen soil is less affected by P. syringae. Warm frozen soil with P. syringae exhibits brittle failure under normal stresses of 100 kPa to 300 kPa and plastic failure under 400 kPa. The shear strength increment can be regulated by the concentration of P. syringae which exponentially relates to ice content and linearly to shear strength. This emerging strategy reveals the importance of INA bacteria in cooling permafrost, and provides a sustainable and environment-friendly method for confronting permafrost degradation and the subsequent infrastructure instability.

The construction of ballastless railway tracks in cold regions is susceptible to frost heave forces, which may particularly impact the stability of track slab cracks and lead to crack propagation. In this paper, the frost heave tests are conducted on the concrete specimens with prefabricated cracks to observe the evolution of the frost heave force within the cracks. The frost heave force is subsequently applied to the finite element model of the concrete specimens to calculate the stress intensity factors (SIFs). In addition, the CRTS III ballastless track model is established to investigate the crack propagation patterns under frost heave and train loads. The results show that the frost heave force in concrete cracks during freezing and thawing is divided into five stages, which produces two peaks of frost heave force. Train loading caused the SIFs of the crack tips to open and close alternately and to rise significantly under the coupling effect of frost heave load. The SIF increases approximately linearly with crack width and is higher for transverse cracks than for longitudinal cracks. Small size cracks do not possess sufficient SIF values to exceed fracture toughness, implying no crack propagation. However, as the crack width is constantly increasing, the SIF will eventually exceed the fracture toughness. Therefore, strict control over track slab's crack width is necessary for CRTS III ballastless tracks.

The issue of frost heave in high-speed railway subgrades located in areas with seasonally frozen soil is a significant concern that impacts both speed and safety, particularly during extreme weather conditions at high altitudes. This research focuses on the Menyuan section of Lanzhou-Xinjiang high-speed railway, where the average altitude is 3400 m and deep seasonal frozen soil exists. Based on field monitoring the temperature, moisture, and deformation of subgrade with coarse particle filler from 2015 to 2022, the research investigates the hydrothermal process of subgrade during freeze-thaw, examines the impact of climate change on frozen depth, and analyzes delamination frost heave. The results show that (1) the annual lowest temperature has a direct impact on frozen depth, which has varied greatly in recent years. The subgrade water content exerts an influence on frozen depth, with most subgrade frozen depth measuring approximately 2.5 m and reaching up to 3.0 m under extreme conditions; (2) By utilizing a waterproof composite geomembrane as an interface, the upper and lower portions of the subgrade can be simplified into two distinct frost heave systems: one without water supply and another with water supply. (3) The frost heave mainly occurs in the depth of 0.7 m to 1.5 m, and the frozen edge appears in the depth of 1.0 m to 1.5 m; (4) The amount of frost heave has a cumulative increasing trend, and the highest frost heave ratio is in the depth of 0.7 m to 1.5 m, followed by the depth of 0 m to 0.7 m, and the depth of 1.5 m to 2.7 m is the least. The findings of this study hold practical significance for enhancing the frost heave mechanism and modifying prediction methods. They also serve as a reference for optimizing the structure, disease prevention, filling selection, and gradation optimization of high-speed railway subgrade in seasonally frozen regions.

Ongoing climate warming and humidification have triggered a series of environmental responses, including vegetation succession, significant permafrost degradation, hydrological shifts, alterations in water resources, and increased frequency of freeze-thaw events. Notably, vegetation modulates the water cycle, regulates soil temperatures, and sustains permafrost stability. However, the extent to which the degradation of alpine vegetation impacts soil hydrothermal processes in permafrost regions is unclear. Therefore, we measured the soil moisture and temperature of the alpine wet meadow (AWM) and extremely degraded alpine wet meadow (EDAWM) ecosystems within the permafrost regions of the Qinghai–Tibet Plateau in situ. The objectives of this study were to explore the freeze-thaw cycles and hydrothermal dynamics within the active layer and to understand the mechanisms behind the effects of extreme alpine vegetation degradation. The results revealed that the AWM ecosystem had a longer soil freezing duration and a higher soil freezing rate than those of the EDAWM ecosystem. Additionally, the freezing index was higher in EDAWM than that in AWM, while differences in the thawing index were insignificant. The variance in the thaw-freeze ratios between the two ecosystems indicated that extreme vegetation degradation in AWM altered soil heat absorption and dissipation in the plant root zone and the deeper active layer. Moreover, EDAWM exhibited a decrease in soil bidirectional freezing processes, particularly from the permafrost table upwards. The extreme degradation in AWM changed soil physical properties and organic matter content, reducing ground temperatures in the active and permafrost layers of EDAWM, particularly during winter. The reduced heat transfer in EDAWM resulted in an active layer depth 9 cm shallower than that in AWM. Without vegetation cover, soil moisture in EDAWM was more prone to evaporation or deeper infiltration, leading to lower soil moisture content than that in AWM. Furthermore, an increase in soil moisture content decreased temperature in shallow soils in AWM but increased it in shallow soils in EDAWM. In summary, extreme vegetation degradation impaired air-heat exchange in AWM soil. These insights provide a scientific and theoretical basis for predicting permafrost evolution in the Qinghai–Tibet Plateau, highlighting the complex interactions among vegetation degradation, soil hydrothermal processes, and climatic factors.