查看更多>>摘要：The cracking of reservoir ice sheets in cold regions is a common natural phenomenon. As the ice cracks develop and the ice grows, the ice sheet will deform greatly, which seriously threatens the safety of the bridge structure. In this paper, the field observation of ice deformation was carried out with the ice sheet of reservoirs in cold regions as the research object, and the deformation law of the ice sheet was studied. Meanwhile, a calculation method for simulating ice cracks was proposed, and the distribution characteristics and cracking process of ice cracks were investigated in combination with the field crack observation results. The main findings of the study are as follows: When the temperature increased, the ice sheet moved in a pattern of expanding from the middle of the reservoir towards the shores. Using the steel trestle bridge as a dividing line, the ice sheet moved to upstream and downstream of the reservoir from the steel trestle bridge location. As temperatures decreased, the ice sheet moved from the shores towards the middle of the reservoir. The ice also moved from the upstream and downstream of the reservoir towards the steel trestle bridge. The study of the generation and extension direction of ice sheet cracks found that the bumps of the shores and the corners of the piers were prone to form cracks. The cracks would extend towards the higher stresses, and the cracks would tend to be connected when the piers and the bumps of the shores were closer. There were four main crack patterns in the reservoir, among which the crack pattern starting from the shore bump and running through the whole ice sheet was prone to produce serious thrust on the piers. The results of the study show that bridges crossing reservoirs are inevitably affected by ice sheet cracking in winter. Therefore, the location selection of new bridges needs to consider the influence of the position of ice cracking and the extension range of cracks to eliminate the safety hazards arising from ice cracking.
查看更多>>摘要：Under the influence of large temperature differences in permafrost regions, liquid water and vapor in the soil accumulate at the bottom of the impermeable layer, forming a pot-cover effect. The phenomenon leads to increased embankment filler porosity, reduces bearing capacity, and exacerbated frost heave and thaw settlement issues. However, the pot-cover effect in embankment in permafrost regions has not yet been verified. This study conducted hydro-thermal transfer experiments using a moisture migration tester and combined numerical simulations to study the migration and accumulation processes of moisture within embankment in permafrost regions, aiming to verify the existence of the pot-cover effect in embankments. Furthermore, based on the watervapor-heat coupling model, this study explores prevention measures for the pot-cover effect through numerical simulation. The results indicate that: (1) the volumetric liquid water content within the soil sample depth range of 0 cm to 30 cm increased by 2.2 % to 4.9 %, confirming the presence of the pot-cover effect in permafrost regions. (2) both liquid water and vapor migrate upwards during the freezing period and downwards during the thawing period. The vapor flux exceeds that of liquid water during freezing, indicating that the moisture accumulation is mainly related to the vapor migration within the soil. (3) when an impermeable layer is placed at a depth of 0.5 m in embankment, the average volumetric liquid water content between 2.5 m and 0.5 m is 15.1 %, closely matching the initial value of 15 %. Thus, installing an impermeable layer at 0.5 m effectively mitigates the pot-cover effect in embankments
查看更多>>摘要：Ice formation is a major problem for many sectors such as aeronautics, power generation, maritime, communications, etc. and therefore, there is a growing demand for anti-icing surface modification technologies. Being able to compare and evaluate these materials at the laboratory scale is a challenge for which a unified response has not yet been given. There are no standards for evaluating icephobicity despite the fact that there are numerous studies focused on the influence of the surface topography on the wetting behavior. In addition, several testing options have been published both for the evaluation of ice accretion, mainly focused on ice wind tunnels (IWT), and on ice to substrate adhesion, as for instance the zero degree cone test, DLST, Cantilever, centrifugal tests, etc. This article describes a method developed to carry out a simple screening evaluation of ice adhesion by the double lap shear test (DLST) method. This technique can provide qualitative ice adhesion information and is commonly available in research laboratories. Moreover, it does not require icing wing tunnel testing. Its ease of execution and reproducibility makes it a useful tool for a first stage evaluation of anti-icing surfaces despite the fact that ice is formed under static conditions. Various materials and surface finished surfaces with different degree of ice adhesion strength were evaluated and were also tested in a centrifugal adhesion test with ice accreted in an IWT. The results showed that the DLST is valid for ice adhesion classification of materials, but shows limitations for those superhydrophobic materials that are in the Cassie-Baxter state.
查看更多>>摘要：In artificial ground freezing (AGF) for tunnel construction, adjusting the freezing patterns can significantly mitigate frost heave and thawing settlements. However, current research on open freezing has not thoroughly explored how different freezing patterns affect frost. This gap in knowledge makes it difficult to provide clear guidance for adjusting freezing patterns in AGF engineering. To address this issue, this paper proposes a predictive model for ice lens width, which can serve as a valuable reference for real-time adjustments of freezing patterns. The model is based on experimental investigations into the freezing rate at the cold side of open freezing under different patterns. Experiment results reveal a correlation between the movement velocity of the freezing front and the ice lens width: a higher velocity results in a narrower ice lens. Based on the second theory of frost heave, a theoretical model for predicting ice lens width under varying freezing rates has been developed, explaining the observed correlation. However, this theoretical model involves many parameters that are difficult to obtain in practical engineering. For the convenience of engineering applications, a simplified model based on the theoretical model was proposed. Validation of this simplified model shows that it has good predictive performance. When combined with a custom temperature sensor, this simplified model offers a solution for real-time monitoring and continuous prediction of tunnel frost heave deformation in AGF engineering.
查看更多>>摘要：In order to determine the pull-out capacity and failure mechanisms of headed stud connectors under freeze-thaw cycles (FTCs), freeze-thaw and pull-out tests were performed on thirty-six pull-out specimens with varying effective embedment depths (60 mm, 90 mm, and 110 mm) subjected to 0, 50, 75, and 100 FTCs. Failure modes, concrete strength, dynamic elastic modulus, mass loss rate, and load-displacement behavior of the specimens after different FTCs were presented and discussed. Experimental results indicated that the degradation of pull-out capacity (Pu) is significantly affected by freeze-thaw damage, particularly after 50 FTCs. Increasing the number of FTCs from 0 to 50 and 100 times, the Pu decreased by 14.9 % and 38.7 %, respectively. Results also indicated that the Pu was enlarged by the magnification of the embedment depth. Increasing the embedment depth from 60 to 90 and 110 mm, the Pu magnified by 65.0 % and 171.1 %, respectively. A finite element (FE) model was further established to gain insight into the effects of concrete strength, effective embedment depth, and stud head diameter on the Pu after FTCs. Numerical results indicated that smaller embedment depths and stud head diameters reduced freeze-thaw resistance, while freeze-thaw damage was minimally influenced by concrete strength. Increasing embedment depth and stud head diameter is recommended to improve the freeze-thaw resistance of pull-out capacity. Furthermore, an analytical model that considers the number of freeze-thaw cycles that is capable of predicting the pull-out capacity of headed studs after freeze-thaw damage was proposed.
Wang, RanCheng, ShaohongTing, David S. -K.Raeesi, Arash...
1.1-1.14页
查看更多>>摘要：Climate change poses many new engineering challenges, such as the increasing number of ice falling incidents on cables of cable-supported bridges. This presents a significant risk to bridge users and society. A thorough understanding of the ice melting process and the impact of weather conditions on its progression is pivotal to elucidate the mechanisms of ice detachment from bridge stay cables and predict its occurrence to prevent any potential ice falling events. The current paper presents a numerical investigation of the transition process from ice to water based on molecular dynamics (MD) simulations using three water models of SPC/E, TIP3P and TIP4P. The water phase change in a piece of pure ice crystal consisting of 3072 atoms is tracked via the tetrahedral order parameter. The performance of these three water models is evaluated based on the predicted ice melting process, melting temperature, numerical stability and computational cost. The impact of thermal conditions, cut-off distance, and ice crystal structure size on the simulated ice melting process are assessed. Ice melting characteristics are revealed by examining the ice cube's internal structure at the molecular level. In addition, the computational efficiency of various CPUs and GPUs in performing MD simulations are compared. The findings from this study not only enhance the understanding of ice melting process at the molecular level, but also provide valuable guidance for optimizing practices in simulations prior to conducting more complex simulations of ice detachment from stay cables.
Aga, JudithaWillmes, ClarissaSinitsyn, Anatoly O.Arlov, Thor Bjorn...
1.1-1.12页
查看更多>>摘要：Permafrost is warming due to changing climatic conditions, a trend that might threaten infrastructure and livelihood across the Arctic. Historical structures are especially vulnerable, as they were not designed to withstand these rapid environmental changes. In the high-Arctic settlement Ny-& Aring;lesund, Svalbard, a large number of historical buildings exist, making the village a suitable case study for investigating the interplay between historical buildings and permafrost. This study analysed two years of ground surface temperature (GST) measurements and snow observations to assess the impact of snow and building management on permafrost conditions in Ny-& Aring;lesund. The mean annual ground surface temperature (MAGST) was found between -1.9 degrees C and 1.9 degrees C in 2022/23, and between -3.1 degrees C and 1.1 degrees C in 2023/24. The results reveal that GST varied substantially within the village area and exceeded the freezing point in several locations. We identified influencing factors contributing to these differences in GST: (i) Snow redistribution by wind and snow ploughing caused large variations in GST with the highest MAGST beneath artificial snow deposits. (ii) Building type, particularly crawl space ventilation, also affected GST. Ventilated crawl spaces tended to lower the MAGST beneath the buildings, while enclosed crawl spaces increased MAGST to positive values. (iii) Building wall orientation further influenced GST, with southern exposures exhibiting higher values compared to northern exposures. Our findings highlight the importance of snow and building management on GST and permafrost stability. Understanding these small scale effects is crucial for the preservation of historical infrastructure on permafrost under changing climatic conditions.
查看更多>>摘要：The impact of emergent boulders within a thinning and melting snowpack remains poorly understood. Our research examines how boulders, exposed by melting snowpack influence the spatial and temporal patterns of snow ablation in the Sha<acute accent>r Shaw Taga` Valley, Yukon, Canada. A multimethod approach, combining thermal infrared time-lapse imaging, drone-based photogrammetry, and terrestrial laser scanning, was used to monitor snow surface temperature, elevation changes, and melt variability. This approach underscores the importance of comprehensive techniques in assessing the spatial and temporal variability of snow surface temperature and topography. Results indicate that boulders accelerate snowmelt in their vicinity during the ablation season, with snow surface thermal characteristics shaped by local terrain and meteorological conditions. The fastest rates of ablation occur during periods of mild weather with no precipitation. These findings highlight the role of boulders as micro-scale heat sources that can modify energy fluxes and influence broader melt patterns in subarctic alpine environments. Understanding these processes is essential for improving snowmelt modelling and predicting hydrological changes in mountain regions affected by climate change.
查看更多>>摘要：In cold regions, the strength and deformation characteristics of frozen soil change over time, displaying different mechanical properties than those of conventional soils. This often results in issues such as ground settlement and deformation. To analyze the rheological characteristics of frozen soil in cold regions, this study conducted triaxial creep tests under various creep deviatoric stresses and established a corresponding Discrete Element Method (DEM) model to examine the micromechanical properties during the creep process of frozen clay. Additionally, the Burgers creep constitutive model was used to theoretically validate the creep deformation test curves. The research findings indicated that frozen clay primarily exhibited attenuated creep behavior. Under low confining pressure and relatively high creep deviatoric stress, non-attenuated creep was more likely to occur. The theoretical model demonstrated good fitting performance, indicating that the Burgers model could effectively describe and predict the creep deformation characteristics of frozen clay. Through discrete element numerical simulations, it was observed that with the increase in axial displacement, particle displacement mainly occurs at both ends of the specimen. Additionally, with the increase in creep deviatoric stress, the specimen exhibits different deformation characteristics, transitioning from volumetric contraction to expansion. At the same time, the vertical contact force chains gradually increase, the trend of particle sliding becomes more pronounced, and internal damage in the specimen progresses from the ends toward the middle.
查看更多>>摘要：Active cooling methods have been widely used to protect the underlying permafrost and maintain subgrade thermal stability. Based on the monitoring data of test expressway embankment in Beiluhe area on the Qinghai-Tibet Plateau, the thermal controlling mechanism of expressway embankment with ventilation duct and open block layer has been revealed by analyzing the heat transfer processes and ground temperature responses. The heat is mainly transferred by forced convection in the horizontal direction and weakly by natural convection in the vertical direction, and the horizontally and vertically equivalent thermal conductivity in cold period is approximately 6.25 and 3 times of that in warm season, respectively, exhibiting thermal semiconductor effect in both directions. The net heat released state is provided for the underlying frozen soil foundation, and the total heat release is approximately 1.2 times of the total heat absorption. A thick and wide cold permafrost layer (T < -1.0 degrees C) has been generated gradually with its permafrost table rising and ground temperature decreasing. Otherwise, it has been found that the decline of wind speed from shady side to sunny side in the block layer contributes to the asymmetrical temperature field of subgrade like the "sunny-shady slope effect". This achievement has deepened the understanding of the cooling methods, and it will contribute to developing the cooling efficiency and optimizing the embankment structure to protect the underlying frozen soil foundation in the warm and high-altitude permafrost regions.
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NSTL
Elsevier