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施工过程中混凝土的入模温度和水化热对多年冻土区桩基施工期间的热稳定性具有重要影响. 针对该问题,利用有限元方法定量研究了±400 kV青藏直流输电线路冻土区锥柱基础入模温度、水化热和含冰量对桩基回冻过程、温度场变化和桩底融化深度的影响规律. 结果表明：水化热影响下,桩基中心温度在第3天达到最高,桩底滞后1 d,基坑表面受其影响较小,主要受环境温度影响;第24天,桩底出现最大融化层,随着入模温度增加,融化层厚度相应增加,入模温度为6℃时融化层厚度为34 cm,15℃时为55 cm;入模温度越高,回冻时间越长,当入模温度为6℃时,完全回冻需经历52 d,15℃时,回冻时间将增加7 d. 含冰量对桩底融化深度有影响,含冰量越大底部融化深度越小;冻土年平均地温是影响桩底融化深度的重要因素,少冰高温（-0.52℃）、低温（-1.5℃和-2.5℃）冻土条件下,最大融化层厚度分别为38 cm、34 cm和25 cm. 基于上述结果,在多年冻土地区的桩基工程,建议混凝土入模温度为6~8℃,底部碎石垫层至少40 cm. 相似文献
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在高原多年冻土地区，气候恶劣，生态环境脆弱。钻孔灌注桩施工中又不可避免地会遇到处于不同冻结状态的土层。施工中必须考虑并设法预防和消除由于冻土的变形、强度弱化及冻胀、融沉所引起的各种危害，因此，钻孔灌注桩施工在质量、安全和环保等方面难度很大。介绍了查钦曲大桥钻孔灌注桩施工工艺，该工艺明显不同于内地通常的钻孔灌注桩施工工艺。在高原多年冻土地区行之有效，对高原多年冻土区钻孔灌注桥施工具有重要的参考意义。 相似文献
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The isotopic composition of solid and liquid portions of natural melting snowpack is investigated in detail by the separating of liquid water from snow grains at different depths of the snowpack. The slope of the δD–δ18O line for the liquid phase is found to be lower than for the solid phase. This is proved to be due to the isotopic fractionation occurring in the melt–freeze mass exchange within the snowpack. Melting of the snowpack has no clear impact on the δD–δ18O line for the solid phase, but the slope of the δD–δ18O line for the liquid shows an overall slight decrease in the melting period. When the snowpack is refrozen, the refreezing process would inevitably cause the slope of the solid phase to decrease because of the discrepancy between the slopes of the two phases. Thus the slope of the solid would become lower and lower as the diurnal melt–freeze episodes cycle throughout the melting season. This effect is then demonstrated by looking into the isotopic composition changes of glacier firn. The extent of the effect depends on the snowpack properties and environmental conditions. The slope changes also result in a decreasing trend in deuterium excess. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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2018年北极太平洋区域夏季海冰物理及光学性质的研究 总被引：2，自引：1，他引：1
The reduction in Arctic sea ice in summer has been reported to have a significant impact on the global climate. In this study, Arctic sea ice/snow at the end of the melting season in 2018 was investigated during CHINARE-2018, in terms of its temperature, salinity, density and textural structure, the snow density, water content and albedo, as well as morphology and albedo of the refreezing melt pond. The interior melting of sea ice caused a strong stratification of temperature, salinity and density. The temperature of sea ice ranged from –0.8℃ to 0℃, and exhibited linear cooling with depth. The average salinity and density of sea ice were approximately 1.3 psu and 825 kg/m~3, respectively, and increased slightly with depth. The first-year sea ice was dominated by columnar grained ice. Snow cover over all the investigated floes was in the melt phase, and the average water content and density were 0.74% and 241 kg/m~3, respectively. The thickness of the thin ice lid ranged from 2.2 cm to 7.0 cm, and the depth of the pond ranged from 1.8 cm to 26.8 cm. The integrated albedo of the refreezing melt pond was in the range of 0.28–0.57. Because of the thin ice lid, the albedo of the melt pond improved to twice as high as that of the mature melt pond. These results provide a reference for the current state of Arctic sea ice and the mechanism of its reduction. 相似文献
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Part of soil around cast-in-place pile will thaw because the heat of hydration produced by concrete during construction. In this paper soil upfreezing action to pile during refreezing process is analyzed, and the measures to the action are put forward. Furthermore, soil frictional forces to pile due to the thawing of part of soil around pile and the slowness of refreezing after construction is discussed and a rational method is suggested. 相似文献
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Carl Egede Bøggild 《水文研究》2007,21(12):1561-1566
In cold Arctic snowpacks, meltwater retention is a significant factor controlling the timing and magnitude of runoff. Meltwater percolates vertically through the snowpack until it reaches an impermeable horizon, whereupon a saturated zone is established. If the underlying media is below the freezing point, accretive ice formation takes place. This process has previously been crudely parameterized or modelled numerically. Such ice is called either superimposed ice on glaciers or basal ice on bare land. Using theory derived from sea‐ice formation, an analytical solution to basal ice growth is proposed. Results are compared against growth rates derived from numerical modelling. In addition, model results are compared to field observations of ice temperatures. The analytical solution is further extended to account for the temperature gradient inside the underlying media and the variable thermal properties of the underlying media. In the analysis, observations and references have predominantly relied on knowledge from glaciers. However, the process of accretive ice growth is equally important in seasonal snow packs with a cold snow‐ground interface and on Arctic sea ice where the ice‐snow interface is well below freezing point. The simplification of this accretive ice growth problem makes the solution attractive for incorporation in large‐scale cryospheric models. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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In the construction of the Qinghai-Tibet Power Transmission Line(QTPTL), cast-in-place piles(CIPPs) are widely applied in areas with unfavorable geological conditions. The thermal regime around piles in permafrost regions greatly affects the stability of the towers as well as the operation of the QTPTL. The casting of piles will markedly affect the thermal regime of the surrounding permafrost because of the casting temperature and the hydration heat of cement. Based on the typical geological and engineering conditions along the QTPTL, thermal disturbance of a CIPP to surrounding permafrost under different casting seasons, pile depths, and casting temperatures were simulated. The results show that the casting season(summer versus winter) can influence the refreezing process of CIPPs, within the first 6 m of pile depth. Sixty days after being cast, CIPPs greater than 6 m in depth can be frozen regardless of which season they were cast, and the foundation could be refrozen after a cold season. Comparing the refreezing characteristics of CIPPs cast in different seasons also showed that, without considering the ground surface conditions, warm seasons are more suitable for casting piles. With the increase of pile depth, the thermal effect of a CIPP on the surrounding soil mainly expands vertically, while the lateral heat disturbance changes little. Deeper, longer CIPPs have better stability. The casting temperature clearly affects the thermal disturbance, and the radius of the melting circle increases with rising casting temperature. The optimal casting temperature is between 2 °C and 9 °C. 相似文献
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寒区桩基热稳定性研究进展 总被引：1，自引：1，他引：0
桩基础锚固长度大、埋置深,对地温场的扰动小、回冻快,在青藏高原多年冻土区被广泛使用。寒区桩基热稳定性研究是一个交叉面广、综合性较强的问题,它涉及到传热学、冻土学、桩基础的设计、桩-土相互作用等多方面的内容。在大量文献基础上,从现场试验、模型试验、理论计算等角度,对寒区桩基热稳定研究现状进行了总结和分析,文献研究表明：土体回冻过程受众多因素影响,而影响程度最大的是混凝土浇筑时的水化热释放;在全球变暖的情形下,未来50年青藏高原冻土退化严重,对桩基热稳定性构成威胁,需要采取相应的保护措施。 相似文献
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