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![Fig. 1. The location of the test pile [38].](profile/Zhaohui-Sun-8/publication/372754089/figure/fig1/AS:11431281178009600@1690757144597/The-location-of-the-test-pile-38_Q320.jpg)
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... high. Due to the lack of physical engineering, this study was only able to construct a small test pile with a diameter of 0.16 m and a length of 4.5 m, which was poured with C30 concrete on July 17. Considering the test pile had no load-bearing requirements, no steel cage was added to the pile. The construction process of the SRP is shown in Fig. 4, which involved bending a copper tube into a U-shape and tying it to thermometric tubes with metal wires. Then, thermometric tubes were placed in the borehole with the copper tube and poured with concrete at 5 °C. After that, the assembled CRS and copper tubes inside the test pile were welded together. Finally, the SPS, the CRS, and ...
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In low-temperature stable permafrost regions, both active and passive cooling measures are commonly employed to ensure the long-term stability of highway structures. However, despite adopting these measures, various types of structural issues caused by permafrost degradation remain prevalent in high-grade highways. This indicates that in addition t...
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... Based on this, they proposed corresponding control measures. To address complex stratigraphic conditions and climate change, engineering measures that utilize artificial active cooling to lower the temperature of formation, thereby creating and stabilizing frozen soil area, are continuously evolving [35][36][37]. By conducting experiments or numerical analysis on the engineering failure modes and sensitivity analysis under various factors, more accurate decision-making regarding such engineering failure risks can be achieved. ...
Under the influence of seepage erosion and nuclide decay heat release, the frozen soil wall constructed by artificial ground freezing method (AGF) to prevent nuclear leakage is prone to occur local ablation and impermeability failure. To ensure its long-term safety and effectiveness, this study conducted a series of laboratory tests to assess the blocking effect of frozen wall to nuclide seepage using the designed impermeability test system. After identifying the critical initial state, the failure mechanism under different conditions was revealed, and a risk decision-making process for AGF disposal of nuclear leakage was proposed. The results show that under the condition of environmental temperature increase, the deterioration effect of frozen wall caused by the cessation of freezing tube is more obvious than that of nuclide continuous seepage. Under the coupling effect of environmental temperature rise and seepage, the monitoring index will appear "pseudo normal" phenomenon and cause the sudden failure of anti-seepage performance of frozen wall at a certain time. The critical temperature and the second critical flow rate determine whether ice crystals appear between soil particles and whether the nuclide solution can penetrate into small pores to further accelerate the deterioration of frozen wall, respectively. It is recommended to determine the risk level in the order of frozen wall temperature, osmotic pressure difference, flow rate, and permeability coefficient. If the risk level is at the fourth level, measures such as increasing the number of freezing pipes and rapid cooling should be taken to quickly respond to the emergency.
... High-latitude permafrost, on the other hand, has a broader distribution, with southern limits ranging from − 1 • C to − 2.5 • C isotherms, encompassing a relatively wide zone of insular permafrost. As a non-homogeneous multiphase material, permafrost consists of soil particles, ice crystals, free water, and gas, with each component interacting with the others to create complex and variable physical and mechanical properties [13,14]. The presence of ice also means that temperature fluctuations can lead to readjustments in the proportions of liquid water and solid ice within the soil. ...
To determine the cooperative variation laws of temperature fields in bridge concrete piles and the surrounding frozen soil during the freezing process in high-latitude, low-altitude insular permafrost regions, we utilized a practical bridge construction project within the frozen soil area of the Daxing'an Mountains, China. This served as the foundation for developing a method to remotely and dynamically monitor the temperatures of piles and soil in permafrost regions, enabling continuous, automatic monitoring of pile-soil temperature data. Employing this automatic temperature monitoring system, we collected temperature data from two 15-m-long concrete bored piles before and after freezing, and monitored the freezing process of the pile foundations in real-time. The cooperative variation laws of the pile-soil temperature field over time were summarized, and a calculation equation for the pile foundation's freezing time was established based on finite element analysis results. Monitoring and analysis reveal that under the influence of the frozen soil temperature field, the pile foundation initially freezes from the bottom up in a unidirectional manner. When the atmospheric temperature falls below 0 °C, the pile foundation freezes simultaneously from both the upper and lower directions. Post-freezing, the internal temperature of the pile body aligns with the surrounding soil temperature, with a temperature difference of less than 0.1 °C at the same depth. For similar in-place temperatures, the freezing time for a test pile with a 1.2m diameter is 1.14 times that of a 1.0m diameter test pile. The range of the hydration heat effect of cement concrete extends 1–2 times the pile diameter.
... Research into shear creep tests at the frozen soil-structure interface and creep constitutive models plays a pivotal role in addressing such issues. The creep deformation patterns at the frozen soil-structure interface are similar to those of frozen soil creep deformation and can be assessed through stress-controlled shear testing apparatus or triaxial testing equipment [2][3][4][5]. Creep deformation in frozen soil refers to the process of elastic-plastic-viscous deformation under constant loading conditions. It is primarily influenced by the temperature, moisture (ice) content, and stress conditions of the frozen soil. ...
The shear creep characteristics of the contact surface between the permafrost and the structure play an important role in the study of the law of deformation and the measures for the prevention and control of pile foundations. In order to study the creep law and the development tendency of the contact surface between permafrost and concrete, it is necessary to establish an accurate creep model. In this study, based on the Nishihara model, a nonlinear element and damage factor D were introduced to establish an intrinsic model of permafrost-concrete contact surfaces considering the effect of shear stress. Creep tests with graded loading of concrete and frozen silt with different roughness at -1°C were conducted using a large stress-controlled shear apparatus. The adequacy of the model was checked using the test data and the regularity of the parameters of the model was investigated. The results show that the creep curves of the contact surface obtained with the improved Nishihara model agree well with the test results and can better describe the whole process of creep of the contact surface of frozen concrete. The analysis of the experimental data shows that: the roughness of the concrete has an inhibiting effect on the creep deformation of the contact surface, When the roughness R varies from 0 mm to 1.225 mm, the specimen corresponds to a long-term strength of 32.84 kPa to 34.57 kPa. For the same roughness and creep time, the creep deformation of the contact surface is more significant with the increasing shear stress τ. The results of the study can provide a theoretical basis for the design and numerical simulation of pile foundations in permafrost regions.
This study aimed to investigate the performance evolution characteristics of concrete under permafrost ambient temperatures and to explore methods to mitigate the thermal perturbation by concrete on the permafrost environment. A program was designed to investigate the properties of various concretes at three curing conditions. The compressive strength development pattern of each group was evaluated and the concrete’s performance was characterized by compressive strength damage degree, hydration temperature and SEM analysis in a low temperature environment. The experimental results show that the incorporation of fly ash alone or incombination with other admixtures in concrete under low-temperature curing does not deteriorate its microstructure, and at the same time, it can slow down the hydration rate of cement and significantly reduce the exothermic heat of hydration of concrete. These findings are expected to provide valuable references for the proportioning design of concrete in permafrost environments.
During the construction of cast-in-place piles in warm permafrost, the heat carried by concrete and the cement hydration reaction can cause strong thermal disturbance to the surrounding permafrost. Since the bearing capacity of the pile is quite small before the full freeze-back, the quick refreezing of the native soils surrounding the cast-in-place pile has become the focus of the infrastructure construction in permafrost. To solve this problem, this paper innovatively puts forward the application of the artificial ground freezing (AGF) method at the end of the curing period of cast-in-place piles in permafrost. A field test on the AGF was conducted at the Beiluhe Observation and Research Station of Frozen Soil Engineering and Environment (34°51.2′ N, 92°56.4′ E) in the Qinghai Tibet Plateau (QTP), and then a 3-D numerical model was established to investigate the thermal performance of piles using AGF under different engineering conditions. Additionally, the long-term thermal performance of piles after the completion of AGF under different conditions was estimated. Field experiment results demonstrate that AGF is an effective method to reduce the refreezing time of the soil surrounding the piles constructed in permafrost terrain, with the ability to reduce the pile-soil interface temperatures to below the natural ground temperature within 3 days. Numerical results further prove that AGF still has a good cooling effect even under unfavorable engineering conditions such as high pouring temperature, large pile diameter, and large pile length. Consequently, the application of this method is meaningful to save the subsequent latency time and solve the problem of thermal disturbance in pile construction in permafrost. The research results are highly relevant for the spread of AGF technology and the rapid building of pile foundations in permafrost.
