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1.
To find the deformation properties of chloride saline soil under the influence of a low temperature environment and different loads,two types of chloride saline soil were selected and their deformation process was tested in the laboratory and analyzed during the cooling process in the sensitive cryogenic temperature range.The research results show that high-chloride-salt saline soil underwent little volume change under the no-load condition during the cooling process.Under staticload and dynamic-load conditions,different degrees of settlement deformation occurred;throughout the entire cooling process,another chloride saline soil with a high proportion of sulfate salt underwent volume expansion under no-load and static-load conditions.Under the no-load condition,a certain degree of settlement deformation occurred.Deformation properties were evaluated at different time points during the cooling process for two kinds of chloride saline soil.Finally, deformation characteristics of chloride saline soil were analyzed from the perspective of salt type and crystallization variation under the action of a low-temperature environment and different loads. 相似文献
2.
Dynamic characteristics of heavy-haul railway subgrade under vibratory loading in cold regions are investigated via low-temperature dynamic triaxial tests with multi-stage cyclic loading process. The relationship between dynamic shear stress and dynamic shear strain of frozen soil of subgrade under train loading and the influence of freezing temperatures on dynamic constitutive relation, dynamic shear modulus and damping ratio are observed in this study. Test results show that the dynamic constitutive relations of the frozen soils with different freezing temperatures comply with the hyperbolic model, in which model parameters a and b decrease with increasing freezing temperature. The dynamic shear modulus of the frozen soils decreases with increasing dynamic shear strains initially, followed by a relatively smooth attenuation tendency, whereas increases with decreasing freezing temperatures. The damping ratios decrease with decreasing freezing temperatures. Two linear functions are defined to express the linear relationships between dynamic shear modulus (damping ratio) and freezing temperature, respectively, in which corresponding linear coefficients are obtained through multiple regression analysis of test data. 相似文献
3.
We consider the problem of year-round cooling of water-saturated soil to freezing temperatures in order to convert it into a state of permafrost.A new soil-cooling apparatus is proposed.The apparatus is to be made in modular form and connected to passive-active thermal piles (thermosyphons).The estimated capacity of one apparatus allows simultaneous use of up to 1,000 thermal piles for ground freezing.The apparatus is based on natural sources of energy:solar radiation and wind;and it can be used for soil freezing.This approach can prevent thawing of soft soils under railways and roads,as well as under buildings or structures,in an area of more than tens of hectares.The apparatus has no mechanical moving parts and can operate for a long time in stand-alone mode without staff involvement. 相似文献
4.
This paper puts forward the coupling model of the heat-moisture-stress field based on the governing equation of
non-stationary heat transfer, moisture movement and the basic differential equations of deformation problem by displacement
under axisymmetric conditions. Using a detailed calculation example for the section of the Xiang Pi Mountain
in 109th National Highway, a mechanical model of the cylinder made by typical silty clay soil is simulated. Results show
that in the coupling process, dynamic stress pays little contribution to the distribution of temperature field along different
depths, and the amount of thawing deformation increased with dynamic loading time under the same frequency and
amplitude. 相似文献
5.
季节性冻融是干旱区土壤盐碱化形成的主要驱动因子,但冻融过程中土壤水盐耦合关系及热量调控机理仍不清楚。通过分析2009年11月～2010年5月新疆玛纳斯河流域典型盐荒地季节性冻融过程中土壤剖面160 cm以内的水分、盐分和温度动态变化,探讨了不同土层冻融过程中水热盐的耦合关系。结果表明：土壤最大冻结深度为150 cm左右,表土层（0～40 cm）温度与气温关系密切;土壤剖面水分呈现“C”型垂直分布,表土层和底土层（100～160 cm）含水量较大,而心土层（40～100 cm）含水量不足10%,土层平均含水率在冻融前期增加了12.91%,而在初蒸期减少了10.01%;土壤剖面盐分在冻结期和初蒸期表聚作用明显,心土层和底土层含盐量稳定,土壤剖面含盐量表现为“积盐-脱盐-再积盐”的变化过程。水热盐之间具有高度协同性,心土层和底土层表现为水盐相随、而表土层为水去盐留的耦合特征,热量传输是调控水盐运移的关键因素。 相似文献
6.
Experiments about working mechanism and mechanical characteristics of the DX model pile foundation under lateral dynamic and static loading were conducted by using a model system of the dynamic frozen ... 相似文献
7.
With the completion of the Qinghai-Tibetan Railway,economic development of related areas has been greatly accelerated.This,in return,calls for building or upgrading more roadways,especially high-grade roadways.In cold regions,the thawing of permafrost can induce settlement damage of and even failure to railway (or roadway) embankments.Thermosyphons (self-powered refrigera-tion devices that are used to help keep the permafrost cool) have proved effective in mitigating thaw settlement by maintaining the thermal stability of the embankments.However,for high-grade roadway embankments of great width,stabilizing or cooling ef-fects of traditional geotechnological measures may be limited.To enhance the cooling effect of thermosyphons,an L-shaped thermosyphon was designed.A laboratory test was carried out to study the combined cooling effect of the L-shaped thermosyphon and thermal insulation applying to roadbed construction.The angle between the evaporator and condenser sections of the L-shaped thermosyphon is 134 degrees,and the L-shaped thermosyphon was inserted into the soil at an angle of 5 degrees with the road surface.The tested results show that the L-shaped thermosyphon is effective in removing heat from a roadway in winter.When the ambient air temperature is lower than the soil temperature,the thermosyphon is active and extracts the heat in the soil around it.When the ambient air temperature is higher than the soil temperature,the thermosyphon is inactive,and no heat is in-jected into the soil through the L-shaped thermosyphon.Compared to embankments with straight thermosyphons,the inner parts of the embankments with L-shaped thermosyphons were significantly cooled.It is hoped that the present study would be useful to the application of L-shaped thermosyphons in the construction of high-grade roadways in cold regions. 相似文献
8.
How freezing and thawing processes affect black-soil aggregate stability in northeastern China 总被引：2，自引：0，他引：2
Laboratory experiments were carried out to investigate the effect of freezing and thawing processes on wet aggregate stability （WAS） of black soil. Wet aggregate stability was determined by different aggregate size groups, different water contents, various freeze-thaw cycles, and various freezing temperatures. The results showed that, when at suitable water content, aggregate stability was enhanced, aggregate sta-bility will be disrupted when moisture content is too high or too low, especially higher water content. Temperature also had a significant ef-fect, but moisture content determined the suitable freezing temperatures for a given soil. Water-stable aggregate （WSA〉0.5）, the total aggre-gate content, and mean weight diameter decreasing with the freeze-thaw cycles increase, reached to 5 percent significance level. The reason for crumbing aggregates is the water and air conflict, thus raising the hypothesis that water content affects the aggregate stability in the process of freezing and thawing. 相似文献
9.
冻融作用与土壤理化效应的关系研究 总被引：19，自引：0，他引：19
冻融使土壤经历一系列物理、化学和生物变化过程,冻融作用对土壤的影响主要表现为:改变土壤结构、含水量分布和水热运动,影响微生物活性和以微生物为媒介的有机质矿化作用,改变土壤元素的生物地球化学循环过程,从而对土壤生态系统结构和功能产生影响。冻融作用对土壤理化性质的作用主要受冻融速率、温度、冻融交替次数和土壤含水量、pH值、有机质、土壤质地状况等因素的影响。通过冻融作用改善土壤结构,提高土壤微生物活性和养分的有效性,有利于耕作和促进植物生长,但也可通过含水量的重新分布和径流淋失而导致土壤养分损失。 相似文献
10.
In order to study the stability of the Qinghai-Tibet Highway embankment at Chumaerhe in the permafrost region of northwest China, the ground temperature and deformation at different depths were monitored under the left and right shoulders of the embankment where thermosyphons were set up only on the left shoulder. Based on the monitored data, characteristics of ground temperature and deformation of the left and right shoulders are analyzed and discussed. The results show that the start time of freezing or thawing of the seasonal active layer was about one to two months later than that of the embankment body itself. The stability of each shoulder was mainly controlled by the settlement of different soil layers,whereasfrost heave of soil had scarcely any effect on the stability of the embankment. For the left shoulder, the settlement was mainly influenced by the seasonal active layer and then by the embankment body itself,due to freeze-thaw cycles which may change the soil properties; however, the permafrost layer remained fairly stable. For the right shoulder, creep of the warm permafrost layer was the main influence factor on its stability, followed by settlement of embankment body itself, and finally settlement of the seasonal active layer. Compared with the deformation of the left shoulder, the permafrost layer under the right shoulder was less stable, which indicates that the thermosyphons had a significantly positive effect on the stability of warm permafrost. 相似文献
11.
Under repeated freezing and thawing in deep seasonal frozen regions, the stability and strength of the soil are imposed in the form of large uneven settlement, instability and strength reduction, which... 相似文献
12.
The unfrozen water content and ice content of frozen soil change continuously with varying temperatures, resulting in the temperature dependence of mechanical properties of frozen soil. Thus the dynamic behavior of embankment in permafrost regions under train loading also alters with seasons. Based on a series of strong-motion tests that were carried out on the traditional embankment of Qinghai-Tibet Railway(QTR) in permafrost regions, the acceleration waveforms recorded at the embankment shoulder and slope toes were obtained. Testing results show an obvious attenuation effect on the vertical train loading from road shoulder to slope toes. Furthermore, numerical simulations of a traditional embankment under vertical train loading in different seasons were conducted, and the dynamic behavior of the embankment was described. The results show that the vibration attenuation in the cold season is greater than that in the warm season. The maximum acceleration of vibration drops to about 5% when the train vibration load is transferred through the embankment into the permafrost, and the high-frequency components are absorbed when the vibration transmits downward. Moreover, the dynamic stress under the dynamic train loading decreases exponentially with an increasing depth in different seasons. The results can be a reference for design and maintenance of embankments in permafrost regions. 相似文献
13.
Freezing and thawing during the winter season change soil properties such as density. The density change in the particulate media influences soil stiffness. In addition, freezing of partially or fully saturated soils changes the soil matrix from a particulate media to a continuum. The goal of this study is to investigate the cyclic freezing and thawing effects on elastic waves. Sand-silt mixtures with 10% silt fraction in weight and 40% saturation are prepared. The sand-silt mixtures are placed in a nylon cell, onto which a pair of bender elements and a pair of piezoelectric disk elements are installed for the measurement of shear and compressional waves, respectively. The temperature of the mixtures decreases from 20°C to 10°C to freezing. The frozen sample is gradually thawed at room temperature (20°C). These freezing-thawing processes are repeated three times. The test result shows that the shear and compressional wave velocities significantly increase when the specimen is frozen. When the temperature is greater than 0°C, the elastic wave velocities are lower during thawing than during freezing due to soil structure change. This study demonstrates that soil structure change during the winter season may be effectively estimated from elastic waves. 相似文献
14.
The effect of climate warming and permafrost thaw on desertification in the Qinghai–Tibetan Plateau 总被引：1，自引：1，他引：0
Four sets of remote sensing images from 1987, 1994, 2000, and 2006, 50 years of meteorological and soil moisture data corresponding to different desertified lands were combined with populations and livestock data to analyze the process and cause of desertification in a portion of the Qinghai–Tibetan Plateau (QTP). It showed that surface soil temperature in the region has increased at an average rate of 0.6 °C per decade between 1980 and 2005, the thawing days on the surface have increased by 60 days from 1983 to 2001, and the depth of the seasonal thawing layer has increased by 54 cm, 102 cm and 77 cm in April, May and June, respectively, from 1983 to 2003. As a result, the upper soil layer has become drier due to the thickening active layer and soil water infiltration. These changes, in turn, have inhibited the growth of alpine meadow vegetation that has shallow root systems. It is concluded that climate warming and permafrost thawing have caused desertification in grazing regions of the Qinghai–Tibetan Plateau (QTP). 相似文献
15.
青藏高原风火山地区冻土变化分析 总被引：1，自引：0，他引：1
基于对多年来风火山地区的多年冻土资料,研究了天然地区和路基下的冻土上限变化情况以及多年冻土的融化状态,并定量分析了进入多年冻土内的热状况。结果表明：风火山地区从20世纪70年代到90年代中期冻土上限下降,冻土出现退化现象,从90年代至今冻土趋于稳定；路基近地表地温明显高于对应天然地表下的地温,路基近地表经历的融化期长于对应天然地表,进入多年冻土区的热收支也呈现出吸热明显大于放热的周期性变化,进入多年冻土的热积累暂时以增高地温耗热为主,但随着冻土吸热量的逐年积累、冻土温度的不断升高,本区冻土可能发生强烈融化。 相似文献
16.
17.
松嫩平原盐沼湿地冻融期水盐动态研究--吉林省长岭县十三泡地区湖滩地为例 总被引：12，自引：0，他引：12
以吉林省长岭县十三泡地区湖滩地为例 ,选取有代表性的月份进行定位观测、实验和对比分析 ,研究了冻融期盐沼湿地水盐运移的特殊规律性。研究表明 ,盐沼湿地冻结期 ,由于冻层的存在 ,土体内产生的温度梯度、水势梯度 ,是冬季水盐积累的驱动力。在冻结期 ,冻层水盐自底层向上迁移 ;融冻期 ,冻层自地表向下及自暖土层向上双向融化 ,在冻层形成上层滞水 ,在冻层之下水盐从下向冻层迁移冻结。冻融期间盐沼湿地水盐迁移的热力学机制是松嫩平原土壤盐化发生机制的重要组成部分。 相似文献
18.
基于Harlan模型和Darcy定律,综合考虑环境气候因素和水热特征参数对湿热迁移影响,建立了环境气候条件下季节性冻土区土壤冻融过程中湿热耦合作用模型.根据地表能量交换平衡原理推导出边界条件.依据实测数据回归分析出土壤湿热特征参数表达式.采用全隐式有限差分格式和TDMA迭代法对内蒙古锡林浩特地区冻结期间土壤湿热迁移规律进行了数值模拟.温度计算值和实测值比较一致,最大误差不超过2.5℃,说明该模型具有较高的准确性.利用该模型仅通过气象资料和湿热特征参数就可预测季冻区土壤冻胀和田间湿热分布状况并能够用来指导农田工程建设和农业生产. 相似文献
19.
以腾格里沙漠东南缘天然植被区藓类结皮、藻地衣结皮斑块荒漠土壤为研究对象,采用原状土培养法,在人工气候箱中设置不同温度（-10、5、15、25、35、40 ℃）培养14 d,测定土壤样品在培养前后NH+4-N和NO-3-N含量,分析两种生物土壤结皮斑块土壤净硝化和净矿化速率对温度的响应。结果表明：①低温培养条件下（-10~15 ℃）土壤氮转化以固持态为主,随着温度升高,尤其当温度超过25 ℃后,藓类结皮、藻地衣结皮斑块土壤净硝化和净氮矿化速率显著提高（p<0.05）;②同一温度培养下,以藓类结皮发育为主的土壤氮转化水平较高,净硝化速率和净氮矿化速率以及无机氮的积累明显大于以藻地衣结皮发育为主的土壤;③两种生物土壤结皮斑块土壤净氮转换速率（硝化和矿化）Q10值在2.46~3.33间波动,其中藓类结皮斑块土壤氮转换对温度的敏感性较高。此外,在土壤氮总矿化过程中,硝化过程具有较强的温度敏感性。高温促进了土壤净氮矿化水平,增加土壤氮有效性,因此可能会对荒漠生态系统的初级生产力产生正向影响作用。 相似文献
20.
中国土壤温度的空间插值方法比较 总被引：15，自引：1，他引：14
利用中国698个气象站点1971~2000年的地面气候资料,采用三种不同方法预测中国0cm、20cm和40cm深度年均土壤温度的空间分布,其中普通克里格和泛克里格法直接以年均土壤温度数据为源数据、回归克里格法以中国年均气温数据和中国DEM数据为源数据进行预测。预测结果的准确性通过平均绝对误差(MAE)和均方根误差(RMSE)值来评价。结果表明回归克里格法预测的MAE值和RMSE值均为最小,说明其预测结果的准确性最好、预测的极端误差也最小;其次为泛克里格法;普通克里格法预测的效果最差。回归克里格法预测结果由于采用了中国DEM数据进行修正,在空间特征表达方面能够更好地表达复杂地形地区的局部变异,其平滑效应明显小于泛克里格法和普通克里格法的预测结果。 相似文献