共查询到18条相似文献，搜索用时 250 毫秒
1.
PIHG Chien－lu ZHAO Lin 《冰川冻土》2002,24(5):517-522
The soil landscape relationship was investigated in the Upper Urumqi River Basin of the Tienshan Mountain Range, Xinjiang, China. Cryosols occurred in glaciated valleys and north-facing toeslopes at elevations above 3 000 m. Most cryosols developed in moraine are Aquiturbels. The microrelief is dominated by earth hummocks, thus the surface organic layers are either discontinuous or broken due to frost action. The Bg horizons are either gleyed or mottled and frost-churned organic matter is common in the lower Bg horizons. Stratified horizons and buried organic or A horizons are also common on gentle sloping or undulating moraines indicating the effects of gelifluction. Reticular structures formed in the lower active layers due to ice lens formation and freeze-thaw cycles. The active layer thickness ranges from 140～200 cm. The organic cryosols (Hemistels) occur in depressions and north-facing toeslopes with an active layer thickness ranging from 90～110 cm. Soils formed on south-facing slopes have a mollic epipedon 20～25 cm thick and a strong brown cambic horizon and are classified as Haplocryolls. The distribution of cryosols is smaller as compared with the extent of permafrost due to the depth requirement of permafrost in cryosol classification. However, the existence of permafrost at greater depth cannot be ignored in land use interpretations. 相似文献
2.
Nikolay V. Ukhov 《冰川冻土》2004,26(Z1):179-183
The rational usage of low productive cryogenic landscapes in the North-Eastern part of Russia is impossible without carrying out special engineering preparation [1]. The preventing from negative that often has destructive cryogenic processes in the area of ice-covered permafrost soils, provided by its thawing into the marginally necessary depth in the whole area. The simplest and the most effective engineering method of faulting as an age-old stock (reserve) of surplus moisture in the form of ice from the upper parts of permafrost soils is the creation of continuous furrows net on the whole surface. This method also raises the fertility of soils, reduces acidity, and raises microbiological activity and the degree of internal structure decaying. Thermophysical calculations and the results of the field study in the experimental firing grounds are the available evidences of this method which raises the thermal stability of cryogenic landscapes while mastering of global climate changes in different parts of cryolithozone. 相似文献
3.
冻融试验对土中含水量分布的影响 总被引：5，自引：0，他引：5
The silty clay and silty loam are two typical soil types obtained from two test sites along the Qinghai-Tibet railway. The two types of soil have been designed various initial dry densities, water eontents, temperature conditions in repeated freezing and thawing tests with free access to water at the bottom. Afterfreeze-thaw cycles, the moisture content in the freeze-thaw zone increases more than that in the unfrozen zone to the peak approximately at the top of the samples. With comparison of the water contents in the frozen and thawed states, the moisture content in the upper freeze-thaw zone in the frozen state is greater than that in the thawed state, while that in unfrozen zone in the frozen state is smaller than that in the thawed state. Within the region of the frost front, the water content in frozen state is smaller than that in thawed state. These findings help to study the freeze-thaw mechanisms deeply and perfect the forecasting module of moisture transferring in freeze-thaw cycles. 相似文献
4.
Kenji Yoshikawa Vladimir Romanovsky Nataria Duxbury Jerry Brown Alexandre Tsapin 《冰川冻土》2004,26(Z1):301-309
Direct current resistivity and ground penetrating radar surveys were employed to obtain the value of the resistivity and dielectric constant in the brine near the Barrow, Alaska. The geophysical surveys were undertaken together with the permafrost drilling program for the measuring of the ground temperature regime and for the core sampling. The sampled cores were measured for their physical and chemical properties in the laboratory under different temperature conditions (-60 to 20 ℃). Laboratory results support field observations and led to the development of a technique for distinguishing freshwater taliks and brine layers in permafrost. These methods were also employed in freshwater taliks near Council,Alaska. The electrical resistivity is a powerful and sensitive parameter for brine detection. However, the resistivity is a less sensitive indicator of the soil type or water content under highly saline conditions.High frequency dielectric constant is an ideal second parameter for the indication of the soil type, liquid water content and other physical properties. The imaginary part of the dielectric constant and resistivity have a significant dependence upon salinity, i.e. upon freezing temperature. The ground temperature regime and the freezing point of the brine layer are important parameters for studying the electric properties of permafrost terrain. 相似文献
5.
Soil freeze-thaw cycles have important effects on surface water and energy balance,and then affect vegetation growth,soil water content,carbon cycle and terrestrial ecosystem. Passive microwave plays an important role in monitoring global and regional surface freeze-thaw processes due to its high temporal resolution,abundant data and sensitivity to soil moisture. With the launch of passive microwave sensors at home and abroad,it provides conditions for the study of permafrost interannual variation,seasonal variation,diurnal variation and long time series of near-surface soil freeze-thaw cycle. In recent years,the study of surface freeze-thaw cycle using passive microwave data has gradually increased. Based on previous studies,this paper summarizes the types of passive microwave remote sensing data and the characteristics of the bands contained in them. Expounded the principle of passive microwave monitoring data used for freezing and thawing,focus on passive microwave data in five categories in the study of freezing and thawing monitoring algorithms,including double index algorithm,the decision tree algorithm,freeze-thaw discriminant algorithm,seasonal threshold algorithm and based on the freezing L-band relative factors discriminant algorithm threshold,and analysis of 5 kinds of algorithms are compared;The freeze-thaw products based on different algorithms and passive microwave data were combed. Finally,the problems and future research directions of passive microwave remote sensing in surface freeze-thaw applications are summarized. In the acquisition of passive microwave data,it is found that the passive microwave data is missing due to the physical characteristics of the sensor,the shape and orbit of the earth,and the low resolution of passive microwave data leads to the low precision of freeze-thaw discrimination. For the problem of missing passive microwave data,it is proposed to use the average value of passive microwave data before and after two days to fill the missing brightness temperature data,or establish statistical function to complement the missing data. For the problem of low passive microwave resolution,the current development trend is to scale down based on passive microwave data and combine with multiple data products,such as ground temperature and active microwave data,or perform probability discrimination on surface freezing-thawing state in pixels,so as to better describe surface freeze-thaw state. In terms of the algorithm for discriminating surface freezing-thawing,based on the problem that dual-index algorithm,decision tree algorithm,freezing-thawing discriminant algorithm and seasonal threshold algorithm cannot accurately distinguish snow and frozen soil,this paper proposes to adopt the method of data assimilation or start from the snow radiation and frozen soil dielectric model. Optimization of the algorithm for the snow covered surface can further improve the accuracy of freeze-thaw classification. Based on existing freeze-thaw products,Although SMAP freeze-thaw products continue to be updated,SAMP satellite was launched late,and SAMP freeze-thaw products have a short time series. In the future,the time span of this algorithm for freezing-thawing products can be extended by combining L-band data provided by SMOS satellite. The problems mentioned above and the direction of further research are of great significance for improving the accuracy of freezing and thawing discrimination and improving the understanding of the variation law of freezing and thawing cycles,and also have certain research space. © 2022 Science Press (China). 相似文献
6.
Seasonally frozen soils are widely distributed in China in terms of area,and the freeze-thaw cycle effect generated by the alternation of cold and warmth is one of the causes of engineering damage in cold areas during construction,and it is particularly important to restore the nature and state of the soil when it is subjected to freeze-thaw action. Therefore,sandy soil specimens with different numbers of freeze-thaw cycles were prepared,and the long-term strength of frozen sandy soil was tested using a spherical template indenter. Using fractal theory and the microstructure image processing software ImageJ,the change law of grain group and long-term strength of two frozen sandy soils under different numbers of freeze-thaw cycles were studied. The results show that：for fine sand（FS）,the fractal dimension DB has a highly significant positive correlation with the long-term strength variation,among which ≥0. 15~0. 20 mm and ≥0. 25~0. 40 mm have the best fit with the long-term strength,and are the dominant grain classes of FS. For medium sand（MS）,the fractal dimension DB is slightly positively correlated with the long-term strength,and the variation shows a“vertical N”trend,in which the grain size content of ≥0. 30~0. 40 mm and ≥0. 40 mm fits better with the long-term strength,and is the dominant grain class for MS. The content of other grain groups did not correlate significantly with the long-term strength change. The freeze-thaw action changed the content ratios of coarse and fine grain agglomerates in the soil. With the increase of the overall particle size interval,the dominant particle size also increases,which shows that the long-term strength of frozen sandy soil tends to decrease and then increase with the increase of the content of some particle sizes. The results of the study can provide theoretical reference for the determination of long-term strength in areas subject to freeze-thaw action. © 2022 Science Press (China). 相似文献
7.
Water accumulation associated with water migration is closely related with the ice segregation,but their coupling relationship is still unclear. To decoupling the relationship of water accumulation and ice segrega⁃ tion,herein,the dynamics of water migration and ice segregation during the freezing and thawing of different soil types under different water supplying conditions have been investigated based on pore water pressure mea⁃ surement and layer-scanning technique. Results showed that apparent water accumulation near the freezing front during the freezing of silty clay and loess tested here,but there exist differences in modes. During loess freezing under closed system,no ice segregation was observed,the pore water pressure increased,and there existed ap⁃ parent liquid water accumulation during the early stage of freezing;while during the freezing of silty clay,there existed ice segregation,the pore water pressure decreased,and no apparent liquid water accumulation occurred during the early stage of freezing. The results implied that there exist two modes of water accumulation near the freezing front during soil freezing：one is the water accumulation induced by water pressure gradient induced by pore ice which results in water flowing from the frozen zone and unfrozen zone to the location near the freezing front;the other is the water accumulation induced by cryo-suction of segregation ice which results in the water flowing from the unfrozen zone to the location near the freezing front. Notably,the contribution from each mode associated with water accumulation of soil freezing depends on whether the ice segregation exists. As no ice seg⁃ regation forms,water accumulation induced water pressure gradient predominates during the early stage of freez⁃ ing. As there exists ice segregation during freezing,water accumulation induced cryo-suction predominates dur⁃ ing the later stage of freezing. Investigating on different modes of water accumulations will be helpful for the ex⁃ ploring the mechanisms of freeze-thaw diseases and the ground ice in the cold regions. © 2023 Chinese Journal of General Practitioners. All rights reserved. 相似文献
8.
Pile foundation is one of the most commonly used and suitable foundations to support transmission line structure, especially in seasonally frozen soil regions and permafrost regions. Axial compression is the controlling condition in the design of foundations for such structures as bridges and buildings, while uplift and overturning will control the design of transmission line structure foundations. This paper presents an extensive overview of previous studies including experimental (e. g., laboratory model test and full-scale field load test), analytical/theoretical (e. g., limit equilibrium and limit analysis based on plasticity)and numerical(e. g., finite difference and finite element methods). The review indicates that study on the uplift behavior of pile foundation in frozen soil is relatively limited, particularly in the case of combined effect of axial uplift and lateral loading. Interaction between pile and frozen soil and mechanism of load transfer along the pile shaft and around the pile tip still remain unclear. Therefore, this paper implements finite difference analysis within FLAC3D to investigate the behavior of pile foundation in frozen silty clay and gravelly sand under axial uplift behavior and the effect of ground condition and lateral loading on the uplift behavior. Because of the axisymmetric condition of the problem studied, only half of the model is simulated. The chosen domain of the medium is discretized into a set of quadrilateral elements and the pile is discretized by the cylinder element. The interaction between the soil and pile is considered according to interface elements. Mohr-Coulomb criterion is adopted to model the soil behavior (perfectly elastic-plastic), while the pile is simply considered as a rigid body. The soil parameters such as Young’s modulus, cohesion and internal friction angle used for numerical analyses are determined by laboratory tests and estimated according to the empirical correlations with in-situ tests. The present numerical modeling is verified with the results from field loading tests on pile foundations in Qinghai-Tibet ±550 kV transmission line project. On this basis, parametric studies are carried out to uncover the behavior of pile in frozen soil. It is observed that pullout is the dominant failure mechanism of pile and the uplift load-displacement curve clearly exhibits an asymptote, consisting of initially linear elastic, nonlinear transition, and finally linear regions. These results are consistent with the observations in a few previous studies. In addition, larger uplift capacity of pile foundation in freezing period and gravelly sand is gained (about 20%). Lateral loading increases the deflection and therefore, decreases the uplift capacity of pile foundation. For the convenience of using the results obtained in practice, the values of uplift factor for pile foundation in silty clay and gravelly sand are provided. Finally, it should be noted that the method used, and the results obtained in the current work could be useful for engineers and designers, at least providing them some qualitative evidence for pile design in seasonally frozen soil regions and permafrost regions. This is important and necessary to ensure the safety of construction in such regions. Meanwhile, numerical analyses in the current work can be a benchmark example for subsequent research studies. © 2022 Science Press (China). 相似文献
9.
The distribution of frozen soil in our country is very broad, and the area of permafrost alone accounts for 22. 4% of the total land area. As a special kind of soil, frozen soil has many properties that thawing soil does not have due to the influence of ice cement in the soil. Among the many properties of frozen soil, the deformation and strength of frozen soil are the basic problems affecting engineering construction in frozen soil areas. The spherical template indenter test is widely used in the test of the mechanical properties of frozen soil because of its simple test process and relatively accurate test results. Compared with the conventional triaxial test or direct shear test, the test process of the spherical template indenter test is simple and easy to implement, the test period is short, and the sample preparation requirements are low. The advantage of effective cohesion is more significant. Therefore, based on the spherical template indenter test of the frozen soil, this paper estimates the strength and mechanical index of the soil through the indentation depth of the spherical template indenter test, and establishes the relationship between the force of the sample and the indentation depth of the indenter test. The specific test method is as follows:take the water-saturated frozen sandy soil made of different particle size groups(the moisture content of the sample is affected by the particle size in the saturated state)as the research object, study the variation law of the depth of the frozen soil sample pressed into the soil by the spherical indenter with time under the conditions of different fixed loads. By comparing and referring to the frozen sands of each particle size group, the long-term equivalent cohesion of the frozen sands of different particle size groups is summarized. The change law of force(long-term shear strength)with time, and the research method of elastic mechanics to solve space problems, summed up the mutual conversion between the depth St of spherical template indenters pressed into frozen sand samples under different fixed load test conditions relation. The research results show that the long-term shear strength of frozen sand based on the spherical mold test is positively correlated with its particle size. At the same time, since the ice content of frozen soil samples is proportional to its particle size, the long-term shear strength of frozen sand is also proportional to the test. The ice content of the sample increases year-on-year;the long-term shear strength of the frozen sand is related to the maximum contact pressure on the contact surface between the frozen soil and the indenter during the test, which can be expressed as Ct = γq0. The size of the relationship coefficient γ is inversely proportional to the diameter of the spherical indenter. In this paper, the spherical indenter is selected as 22 mm, and γ=3. 82×10-3. By establishing the relationship between the maximum contact pressure q0 and the long-term shear strength Ct When the maximum contact pressure q0 is the same under different fixed loads, the long-term shear strength Ct is also the same. According to this, the depth curve and the freezing depth of the frozen sand pressed into the soil by the spherical indenter over time under different fixed loads can be converted. Long-term shear strength curve of frozen sandy soil with time. It has been verified by experiments that the conversion curve of the depth of the indenter pressed into the soil with time under a fixed load of 7. 0 kg is highly consistent with the measured curve of the depth of the indenter pressed into the soil with time under a fixed load of 5. 1 kg and 7. 0 kg. © 2022 Nanjing Forestry University. All rights reserved. 相似文献
10.
As the globally largest area covered by high altitudinal permafrost, the Qinghai-Tibet Plateau may contribute substantially to atmospheric CH4 budget when global warming. Preliminary observations on CH4 emission at Qingshuihe from November 5 to 14, 1995 show that alpine grassland may be a small source for atmospheric CH4 during early winter. The emission rates of CH4 from moist grassland surface varied from-16. 1 to 23. 9 μg. m-2h-1, with an average of 1. 82 μg. m-2h-1. Emission rates of CH4 from water surface of Qingshuihe River were from -21. 0 to 37. 1 μg. m-2h-1, with an average of 1. 56 μg. m-2h-1. The emission rates of CH at 30 to 200 cm in depth ranged from-69. 0 to 36. 0 μg. m-2h-1, with the average rate at these depths varying from -2. 15 to 2. 04 μg' m-2h-1. The mean emission rates of CH4 in the active layer and permafrost indicate the lower part of active layer tends to release CH4, CH4 is absorbed at low rates in the middle section and in the vicinity of permafrost table, and net fluxes of CH4 is emitted from the soils in the upper part. During the observation periods, the methane concentrations in static chambers and emission rates of grassland and water surface displayed noticeable diurnal variations. The water/ice content may play important role in the spatial variations of methane emission rates. The emission rates of methane is weakly correlated with the ground temperatures at sampling depths and air temperatures. The observed emission rates of methane from the comparatively dry and sandy grassland soils are quite low compared with that observed in the permafrost regions in the high latitudes. 相似文献
11.
冻融循环对土的结构以及物理力学性质有着重要影响,其变化与冻融过程中的孔隙水压力变化有密切关系。但土体冻结过程中的孔隙水压力测试一直是冻土土工测试试验的技术难题。针对这一难题,研发了一种适用于冻结土体孔隙水压力测试的探头,并对砂土和粉质黏土在冻融循环过程中的孔隙水压力发展变化进行了实时监测,获得了圆柱试样冻融循环过程中不同深度处的孔隙水压力变化过程。在冻结过程中,粉质黏土形成冻结缘区及可视的分凝冰,而砂土则无冻结缘及分凝冰的形成。冻融循环过程中土体内部的孔隙水压力变化受温度、冻结速率、冻融循环以及土质等因素的影响。孔隙水压力随温度的循环变化而经历周期性变化：冻结过程中,孔隙水压力不断下降,吸力不断增加;融化过程中,孔隙水压力增大。而冻结速率、冻融循环及土质主要对孔隙水压力降的幅值变化产生影响。此外,冻结锋面位置附近孔隙水压力的下降、吸力的增加,正是水分由未冻区向冻结区迁移的主要驱动力。根据以上试验结果及其理论分析发现,所研制的孔隙水压力探头具有一定的实用性。 相似文献
12.
多年冻土区斜坡稳定性研究综述 总被引：1，自引：0，他引：1
全球变暖、极端天气频发,引发的地质灾害对自然生态环境和人类生产生活造成了很大的影响。尤其对气候变化较为敏感的高温（年平均地温>-1 °C）和高含冰量多年冻土区,气候变暖以及人类活动导致的冻融地质灾害日益频繁。冻土退化条件下,土体结构和物理力学性质发生改变,黏聚力和抗剪强度降低,造成多年冻土区斜坡发生滑坡、崩塌、泥流等灾害。斜坡失稳加剧了多年冻土区脆弱生态环境的恶化,同时对建（构）筑物安全运营产生威胁。与非冻土区相比,多年冻土区斜坡稳定性研究主要针对高含冰量斜坡段,斜坡失稳模式主要以热融滑塌和活动层滑脱为主。热融滑塌由斜坡段地下冰暴露融化引起,而活动层滑脱产生的原因是冻土融化导致土体孔隙水压力过大,形成的超孔隙水压力降低了土体强度,造成斜坡失稳。此外,多年冻土区斜坡失稳模式还包括融冻泥流、崩塌以及蠕变滑坡等。通过综述近期多年冻土区斜坡稳定性研究进展,概括了多年冻土区斜坡失稳的模式、特征、影响因素、失稳机理、分析方法及防治措施等,并对未来多年冻土区斜坡失稳的研究重点提出建议。 相似文献
13.
建立了粗、细粒土冻结模型, 分析了扰动三层体内部的析冰原理, 提出密闭水体的冻结-压力循环, 该循环是涎流冰发育的机理. 对饱水粗颗粒土与饱水细颗粒土的冻结模型比较表明, 饱水粗粒土在密闭体系中的冻结; 就其产生的水压力而言, 实质上就是密闭水体的冻结, 也就是水冻结成冰体积膨胀受限而产生力的问题. 这种体积膨胀产生的力导致约束结构(如薄弱层)的整体性破坏. 在公路边坡数值模拟分析的基础上, 提出边坡薄弱层破坏导致渗水是形成坡积冰的主要原因之一, 薄弱层破坏处是病害最严重的位置. 根据病害形成原理和成因分析, 并提出渗井与仰斜式排水管相结合的复合防治措施, 工后效果良好. 相似文献
14.
A.R. Jumikis 《Engineering Geology》1979,13(1-4):125-135
This paper elucidates some factors affecting the formation of soil cryogenic textures upon artificial active and passive soil freezing to form a soil-ice wall cofferdam.
Depending upon the soil type, the thermal regimen of the stages of active and passive freezing of the soil-ice wall brings about various kinds of cryogenic textures. The cryogenic textures, in thier turn, affect the strength of the artificially frozen soil-ice wall.
It is shown that upon loading, the variously oriented hexagonally crystallized ice crystals, upon application of externally applied loads, may become subjected to compression or bending or shear stresses, and/or to a combination of such stresses. Also, sustained loads on a frozen soil may bring about time-dependent, long-term deformation of the ice, viz., frozen soil, known as the rheological phenomenon creep.
It is postulated that the strength and performance of the composite frozen soil—the ice wall—is a function of its components, such as the soil cryogenic texture, its thermal regimen and the strength of the ice. It is also pointed out that the performance of the ice wall should be evaluated in terms of its strength and strains. 相似文献
15.
冻土的力学性质及研究现状 总被引：18，自引：1，他引：17
中国具有广大的季节冻土和多年冻土区,在冻土地区进行工程建设,就必须深入研究冻土的力学特性,以确保冻土地基上工程建筑物的稳定性。本文首先,简要介绍了我国冻土的分布状况和冻土区别于融土的基本特性,广义的冻土力学可分为冻融作用和已冻土力学性质两方面,冻胀、融沉和冻融循环引起的土力学性质的变化属于冻融作用的范畴。对于冻胀的研究较为深入,人们先后提出了多个理论来解释冻胀产生的机制,有的应用于计算分析中。对融沉的研究尽管具有较长的历史,但是多数停留在经验方法上,融化固结理论目前还有较大的局限性,因此提出一方面可以用人工神经网络法提高经验方法的精度和适用范围,另一方面应当发展融化固结大变形理论;冻融循环可以改变土的力学性质,介绍了作者的最近研究进展。针对已冻土的力学特性,从3方面进行了分析。冻土的强度主要沿用融土的强度理论,很难反映高应力下的压融现象;冻土动力学特性主要针对温度对动力学参数的影响,近年来冻土层对场地动力响应的影响越来越受到重视;冻土的本构关系多集中在蠕变研究,以经验公式法为主。最后,分析了多年冻土地区工程变形所涉及的物理力学过程。 相似文献
16.
17.
深上限-退化型多年冻土路基变形特征分析 总被引：1，自引：0，他引：1
为了研究深上限-退化型多年冻土路基变形特点,基于青藏公路多年冻土路基地温和沉降现场监测资料,通过分析西大滩、唐古拉山北坡以及唐古拉山南坡路段的土质、冻土含冰量、冻土地温以及路基沉降变形数据,对冻土上限变化过程与路基沉降特点进行了研究,同时对沱沱河和清水河地区冻土路基分层沉降观测结果进行了分析。结果表明,土质和含冰量对退化型冻土路基的沉降变形影响较大,深冻土层的融化对路基沉降变形影响较小,退化型冻土路基的沉降变形主要发生在退化后的冻土层中,退化冻土层在冻融循环过程中,需要较长时间才能完成固结。对于冻土含冰量为少冰、多冰的稳定路段,退化冻土路基年平均沉降速度约为3.9～5.6 mm/a,路基沉降量极小;对于含冰量较高且土质以粉黏性颗粒为主的不稳定路段,路基沉降速度具有持续性和无减缓性的特点,路基年平均沉降量达到0.03 m/a,路基变形表现为整体均匀沉降,横向差异沉降量较小。 相似文献
18.
受冰-水间相变影响, 冻融期内土壤水、热传输过程变得复杂, 研究气态水分布特征与运移规律, 可为厘清冻融过程中沙地包气带水文循环机理提供关键信息。通过在毛乌素沙地建立原位监测点, 并利用修改后的Hydrus-1D冻融程序建立包气带水-汽-冰-热耦合数值模型, 对冻融期包气带气态水迁移过程展开研究。结果表明: 模拟与实测土壤水分及温度变化拟合较好, 证实所建立的模型具有良好的精度以及适用性; 对比典型未冻结、初始冻结、向下冻结以及融化时段结果可知, 冻融过程会改变剖面土壤水分、含冰量以及水汽密度分布, 其中水汽密度变化与温度联系紧密; 冻结后, 由温度梯度驱动的非等温气态水通量在总水分通量中的占比超过90%, 表明气态水占据主导地位, 其运移过程对于剖面土壤水分分布以及高含水量带出现有重要影响。 相似文献