Cold Regions Science and Technology最新文献

The combined effect of parameters like surface stiffness, topography, and interface size on ice adhesion and its interfacial fracture behavior was studied. Ice adhesion on aluminum and polyurethane with three different surface roughness and two different surface sizes was evaluated experimentally through mode II interfacial fracture tests on a previously formed block of ice. Results showed that, for stiff surfaces the surface roughness increases the adhesion significantly, due to the transition from adhesive to cohesive fracture. Compliant surfaces do not show this transition, in the same roughness scale due to its susceptibility to deformation. The force required to fracture an ice block from stiff surfaces stabilize after a certain length, while compliant surfaces do not show this transition at the length scales studied. The article elucidates the relevance of different parameters and the consideration of size scales for designing low ice adhesion surfaces.

Damage development in rocks by freeze-thaw cycles, a phenomenon that is typical to cold regions, is known to reduce the strength and durability of structures. In this study, a series of freeze-thaw tests were performed on frost and non-frost heave rocks to examine the impact of frost heave susceptibility and temperature-changing conditions on rock behaviors. The freeze-thaw life and uniaxial compressive strength (UCS) of rocks subjected to freeze-thaw cycles were estimated using a model that was based on fatigue damage mechanisms. Furthermore, we proposed a method for estimating the freeze-thaw life of rocks, using expansive strain as an important factor. The results indicated that the Shikotsu welded tuff (a non-frost heave rock) exhibited higher durability than the Noboribetsu welded tuff (a frost heave rock); this may be because the Shikotsu welded tuff had a larger pore radius and more unsaturated pores. The one-dimensional (1D) cooling-heating conditions induced significantly less damage than the three-dimensional (3D) conditions, owing to the continuous migration of free water into the unfrozen zone. The damage model estimated that for the Noboribetsu welded tuff, the freeze-thaw life in the 1D conditions was approximately eight times longer than that in the 3D conditions. Notably, with respect to the Shikotsu welded tuff, a critical freeze-thaw period induced significant expansion, resulting in damage development in the tuff. The freeze-thaw life of each rock sample was estimated based on the magnitude of the volumetric expansive strain. This study contributes to the rational assessment of the stability and durability of rock structures in cold regions.

The water-salt migration law and deformation characteristics of coarse-grained saline soils have been extensively studied and illustrated. However, owing to the influence of the chemical composition and physical properties of the soils, coarse-grained soils are prone to localized soil absorption during mixing and compaction. This type of working condition of the existing localized fine sand accumulation layers is seldom discussed in the literature. In this study, water-salt migration and deformation of natural gradation specimens and specimens with localized fine sand accumulation layers in natural gradation were monitored and detected for the field fill conditions in an airport embankment project using self-designed test equipment based on nine freeze–thaw cycle physical simulation tests at environmental temperatures ranging from −30 °C to 25 °C. Under the freeze–thaw cycle, compared with the natural gradation, the specimens with localized fine sand accumulation layers had a higher influence on water and salt migration, which indicates that the depth range of drastic changes in water and salt increased by 80% and 84%, respectively. The cumulative deformation curves under the effects of natural gradation and localized fine sand accumulation exhibited similar trends. The difference between the deformation of the natural samples and samples with localized fine sand accumulation layers was 16% when the salt content of the upper part of the roadbed was 0.3%. In addition, the cumulative vertical settlement deformation of the specimens decreased with an increase in the salt content of the upper part of the roadbed and gradually transformed into vertical uplift deformation. The results of this study provide a basis for the selection of materials for airport roadbed backfill and their application in construction in seasonally frozen areas.

The West of Kunlun Mountain Pass Ms8.1 earthquake in 2001 on the Qinhai-Tibet plateau is one of largest earthquakes in the permafrost regions on the globe. This earthquake event caused the ground surface rupture zone having the length of 426 km with the ground fissures about 10-30cm wide, seismic subsidence up to the maxium value of 20 cm. Moreover, the earthquake triggered liquefactions along shores of lakes and banks of rivers, landslides of a dam and collapse of slopes, and avalanches. The characteristics of the earthquake disasters were studied through on-site investigation, geophysical survey， laboratory tests of the soil samples and numerical analysis of the dynamic behaviors. Furthermore, the relevant prevention measures for engineering projects were proposed which would provide valuable scientific basis for earthquake disaster mitigation in cold regions.

Recently, with the increase in global temperature, the permafrost degradation trend has intensified, and the soil-rock binary slope in permafrost regions has become more unstable. Therefore, this paper focuses on the shear strength of the clay-rock interface in the binary slope. The three-dimensional roughness, freezing temperature, and normal stress are key factors affecting the shear strength of the clay-rock interface. The influence of freezing temperature can be further quantified by using the unfrozen water content (UWC), which was measured by nuclear magnetic resonance (NMR) technology. By analyzing experimental results, it can be concluded that the three-dimensional roughness can effectively improve the shear strength of the clay-rock interface under freezing conditions, and the shear strength increases with the growth of the climbing angle (i_c). The influence of temperature can be attributed to the effect of UWC on the internal friction angle and cohesion of saturated clay. Compared with the internal friction angle, the cohesion of saturated clay decreases faster with the increase of UWC. In addition, the shear strength of the clay-rock interface rises linearly as the normal stress increases, therefore the Mohr-Coulomb criterion also can be used to characterize the shear strength of the clay-rock interface. An interesting finding is that significant tensile cracks will appear in the clay part around the large bulge under low normal stress and high roughness. It further confirmed the contribution of large bulges to the prevention of shear slides of soft clay. The quantification understanding of the shear mechanical action of the clay-rock interface can provide a reference for scientific disaster reduction in cold regions.

Electrical resistivity tomography (ERT) is an effective method for detecting the distribution of permafrost. However, the general inversion method of ERT cannot satisfy the engineering designation demand, resulting in the foundation of thaw settlement in discontinuous permafrost regions. In this study, we proposed a neural network-ensemble learning inversion method to improve the detection accuracy of discontinuous permafrost. First, a series of different resistivity distributions was evaluated to establish forward models for the training of a backpropagation neural network (BPNN). The resistivity distributions of the forward models varied with the temperature gradient, similar to the resistivity distribution of real discontinuous permafrost. The bagging algorithm of ensemble learning was then used to optimize the BPNN inversion models. Finally, three discontinuous permafrost resistivity models and two field data examples are considered to demonstrate the feasibility of the proposed inversion model. The inversion results of synthetic and field examples show that the neural network-ensemble learning model achieved a greater inversion effect with better accuracy and less noisy points than a single BPNN model or the Res2Dinv method. The trained ensemble learning inversion method has good application in field permafrost exploration.

Studying train-induced response characteristics is essential for safely operating permafrost railway subgrades. A three-dimensional thermal-mechanical coupling nonlinear dynamic model of train-track-subgrade-ground relationships was established to analyse the train-induced dynamic stress, acceleration and stress path characteristics of a permafrost railway subgrade, and field monitoring data were used to verify this model. The differences between the 2D and 3D models are also discussed, along with the seasonal changes, train speed, axle load, and train type affecting permafrost subgrades. The main results are as follows. First, the vibration load significantly impacts the subgrade 6 m below the sleeper, producing distinct vertical dynamic stress waves due to the wheels and bogies. Dynamic compression stress dominates the subgrade and is influenced by the train structure, speed, and sleeper spacing. While the 2D model tends to underestimate the dynamic stress in shallower layers, it concurs with the 3D model in deeper subgrade dynamics within a 10% margin of error. Then, the principal stress axis of the subgrade soil rotates synchronously with train movements, exhibiting regular stress paths in the YZ plane (longitudinal section) with depth-dependent variations in the stress cycles and deviatoric stress. Finally, predominantly originating from sleeper-induced vibrations, the subgrade vibration acceleration varies with the train speed, sleeper spacing, and season and is most pronounced in the vertical direction. This study provides theoretical guidance for the vibration response of permafrost subgrades on the Qinghai-Tibet Railway (QTR).

The complexity of the load response on a modern cross-country ski makes it difficult to address the individual macroscopic parameters' influence on ski-snow friction. In this study, a custom adjustable ski was developed to isolate the effect of normal force, apparent contact area, spacing and load split on the coefficient of friction. These parameters were tested in a ski-snow tribometer at relevant sliding speeds, normal loads, slider sizes and snow conditions for cross-country skiing. At cold air temperatures (−10 °C) the friction was governed by the average contact pressure, whereas at warmer air temperatures (−2 °C and + 5 °C) the friction was governed by the apparent contact area. Additionally, the effect of load split between the front and rear slider showed different trends depending on the temperature. Smaller spacing between the two sliders led to reduced friction across all temperatures. These findings provide new insights for optimizing cross-country ski gliding performance in various snow conditions.

Atmospheric icing, the accumulation of ice on surfaces, is a severe concern for the aviation industry. Deicing and icing prediction tools are necessary for pilots to ensure flight safety, and while there is established technology for large aircraft icing, more research is needed for smaller uncrewed aerial vehicles (UAVs). Here, we present measurements from 59 flights of a multirotor UAV into wintertime low stratus clouds of temperatures between $-$3 and $-$10 °C. The UAV is equipped with rotor heating to allow flights up to 10 min in icing conditions. Icing severity was quantified by using the rate of increase in battery current during icing, and was then compared with simultaneous, co-located measurements of liquid water content (LWC). LWC measurements were (a) calculated from cloud droplets measured with an in situ holographic imager on a tethered balloon system and (b) retrieved from remote sensing observations (microwave radiometer, ceilometer, cloud radar). We show that, for these environmental conditions, icing was strongly positively correlated to LWC over an LWC range of 0.02 to 0.5 g m⁻³, independent of temperature and mean droplet size, though droplets $>50$ $\mathrm{\mu m}$ in diameter may contribute to increased icing severity. We also show that the LWC retrieved from remote sensing agrees well with the in situ measurements, indicating that remote sensing measurements can effectively be used to assess icing conditions. These are the first known measurements of multirotor UAV icing with co-located LWC measurements in natural clouds.

Unfrozen water content is a key concern in frozen soil. The measurement of unfrozen water using nuclear magnetic resonance (NMR) has gained significant popularity. However, the extraction methods of unfrozen water content from NMR data are still lack of a comprehensive evaluation. To overcome this challenge, a constant unfrozen water test (three representative soils, i.e., silty clay, bentonite clay, and silt sand, are selected) is proposed and used to study on the influence of temperature on NMR signal. Further, three extraction methods of unfrozen water content, such as the Curie law method (CLM), paramagnetic regression line (PRL) method, and resistivity-temperature method (RTM), are evaluated. The results demonstrate that: (1) As a theoretical method, CLM is the most convenient but with the highest error, as an average water content error of 0.74%. (2) PRL requires four calibration points and has an average water content error of 0.28%. (3) RTM needs a special calibration curve and yields the smallest water content error of 0.07%. Overall, RTM with a pre-calibrated λ is recommended to obtain higher precision and PRL can be employed as a convenience choice.