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1.
Recent years have seen a large number of high-speed railways built and will be built in seasonal frozen soil regions of China. Although high-speed railways are characterized by being fast, comfortable and safe, higher standards for deformation of the railways' frozen subgrade are required. Meanwhile, changes in subgrade soil temperatures are the main factors affecting the deformation of frozen subgrade. Therefore, this paper selected typical test subgrade sections of the Harbin–Qiqihar Line, a special line for passenger transport built in the deep seasonal frozen soil regions of China, to monitor field temperatures. Also, the temperature changing laws of railways' subgrade in this region was analyzed by using testing data, the aim of which is to provide a technical support for future design and construction of buildings and structures in a deep seasonal frozen soil region. 相似文献
2.
To investigate the vibration characteristics of a railway subgrade in different seasons, three field experiments were carried out in
the seasonally frozen Daqing area of China during spring, summer, and winter. The vibration characteristics and attenuation rates
of the subgrade induced by passing trains were investigated, and the influences of the season, train speed, train type, train load, and
number of train compartments are described in this paper. The results show that: (1) near the rail track the vibration in the vertical
direction was more significant than in the lateral and longitudinal directions, and as the distance from the railway track increased,
the acceleration amplitudes and the attenuation rates all decreased in all three directions; (2) the acceleration amplitudes and attenuation
rates decreased in the three different study seasons as the distance from the railway track increased, and the attenuation
rates in the freezing period were the largest; and (3) the acceleration amplitude induced by a freight train was greater than that by a
passenger train, and the subgrade vibration increased with increasing passenger train speeds when the number of train compartments
was similar. These results have great significance for enhanced understanding of the characteristics of train-induced vibration
embankment response in seasonally frozen regions, and provide essential field monitoring data on train-induced vibrations in
order to improve the performance criteria of railroading in seasonally frozen regions. 相似文献
3.
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
4.
以1981—2018年内蒙古典型草原季节性冻土为研究对象,通过气候倾向率、Mann-Kendall法、多元线性回归等方法,分析最大冻土时空分布特征、年际、年代际变化,研究影响最大冻土深度变化的气象因子。结果表明：（1） 内蒙古典型草原季节性冻土冻结初日在9—11月,终日在4—6月,年内最大冻土深度出现在2—3月,深度在100~280 cm之间。（2） 最大冻土深度年际变化分为下开口抛物线型、上开口抛物线型、正弦曲线型,从最大冻土深度气候倾向率看呈现减小趋势的站点有68%。（3） 最大冻土深度年代际变化分为逐年代递减、减-增型和无明显变化规律,50%的站点在1989年以后最大冻土深度发生突变。（4） 多元线性回归表明气温冻结指数、年平均风速、年极端最低气温对最大冻土深度产生显著影响。该研究揭示了最大冻土深度存在退化的事实,为草原应对气候变化提供指导,为陆地土壤和大气碳循环交换的研究给出提示。 相似文献
5.
In the numerical simulation of long-term subgrade temperature fields, the daily variation of soil temperature at a certain depth h is negligible. Such phenomenon is called the "boundary layer theory."Depth h is defined as the boundary layerthickness and the soil temperature at h is approximately equal to a temperature increment plus the average atmosphere temperature. In the past, the boundary layer thickness and temperature increment were usually extracted from monitored data in the field. In this paper, a method is proposed to determinate the boundary layer thickness and temperature increment. Based on the typical designs of highway or railway, the theoretical solution of boundary layer thickness is inferred and listed. Further, the empirical equation and design chart for determining the temperature increment are given in which the following factors are addressed, including solar radiation, equivalent thermal diffusivity and convective heat-transfer coefficient. Using these equations or design charts, the boundary layer thickness and temperature increment can be easily determined and used in the simulation of long-term subgrade temperature fields. Finally, an example is conducted and used to verify the method. The result shows that the proposed method for determining the upper thermal boundary of subgrade is accurate and practical. 相似文献
6.
In seasonally frozen regions, the frost-heave properties of soil play a significant role in its upper-structure performance and durability. To investigate the frost-heave behaviors of saturated, compacted silty clay soil widely used as subgrade material, a series of one-side freezing tests was carried out; and the freezing depth and frozen front effected by the compactness, temperature, overburden pressure, and water-supply condition were analyzed and discussed. The results show that the moving speed of the frozen front and growth rate of the frozen depth are positively correlated. The frost heave is maximum in the frost-heave stability condition. The frost ratio of saturated soil is proportional to the water supply and cooling temperature under a one-side freezing condition. The frost ratio of saturated soil is inversely proportional to the initial compactness of the soil specimen and the overburden pressure. 相似文献
7.
《寒旱区科学》2021,(4)
Ground temperature plays a significant role in the interaction between the land surface and atmosphere on the Tibetan Plateau(TP). Under the background of temperature warming, the TP has witnessed an accelerated warming trend in frozen ground temperature, an increasing active layer thickness, and the melting of underground ice. Based on high-resolution ground temperature data observed from 1997 to 2012 on the northern TP, the trend of ground temperature at each observation site and its response to climate change were analyzed. The results showed that while the ground temperature at different soil depths showed a strong warming trend over the observation period, the warming in winter is more significant than that in summer. The warming rate of daily minimum ground temperature was greater than that of daily maximum ground temperature at the TTH and MS3608 sites. During the study period, thawing occurred earlier, whereas freezing happened later, resulting in shortened freezing season and a thinner frozen layer at the BJ site. And a zero-curtain effect develops when the soil begins to thaw or freeze in spring and autumn. From 1997 to 2012, the average summer air temperature and precipitation in summer and winter from six meteorological stations along the Qinghai-Tibet highway also demonstrated an increasing trend, with a more significant temperature increase in winter than in summer. The ground temperature showed an obvious response to air temperature warming, but the trend varied significantly with soil depths due to soil heterogeneity. 相似文献
8.
On the basis of on-site measured data of the newly constructed Gonghe-Yushu Highway in a permafrost region, this paper analyzed thermal conditions of the subgrade with XPS insulated board according to different selected monitoring sections in various locations. We also summarized the geothermal distribution and change rules of subgrade with XPS insulation board under the asphalt pavement in summarized a high temperature frozen soil region. It is suggested that the shoulder of subgrade with XPS insulation board be widen to a reasonable width so as to keep the subgrade stable. 相似文献
9.
Accounting for the solar radiation in thermal regime prediction for railway subgrade in cold regions
This paper presents a comparative analysis of simulation processes of seasonal freezing-thawing of railway subgrade and permafrost degradation, with and without accounting for solar radiation. Also, the effect of sun screens to reduce the degradation of subgrade permafrost under different climatic conditions is numerically substantiated. And finally, the temperature criterion of the origination of permafrost is illustrated. 相似文献
10.
In order to study the shear behavior of coarse-grained fillings taken from the subgrade bottom layer of a cold region high-speed railway, large scale direct shear tests were conducted with different normal pressures, water contents and temperatures. The results indicate that the relationship between shear displacement and shear stress changed from strain-softening at lower normal pressures to strain-hardening at higher normal pressures, in both unfrozen and frozen states. This phenomenon was mainly due to the shear dilatation deformation effect. The shear displacement-shear stress curves show similar stages. Besides, the shear stress rapidly increased and there was not an increment in the shear displacement during the initial stage of the shear process in the frozen state. In both the unfrozen or frozen states at the same water contents, the shear strength increased with increasing normal pressure. 相似文献
11.
Numerical simulation is known as an effective method for mechanical properties during frozen soil excavation. In order to reveal the development of cutting force, effective stress and cutting fragments in frozen silt during the cutting process, we introduce an explicit finite element program LS-DYNA to establish a two-dimensional numerical model of the frozen soil cut. We also use the Holmquist-Johnson-Cook(HJC) damage constitutive model for simulating the variation of soil mechanical properties according to the strong dependence between the cutting tool and frozen silt during the process with different cutting depths, angles and velocities. Meanwhile, a series of experimental results are acquired of frozen silt cutting to prove the application of the HJC model during simulation of cutting force variations. The result shows that the cutting force and fragment size are strongly influenced by cutting depths and cutting velocities increased, and the maximum effective stress at points where the tool contacts frozen soil during the cutting process. In addition, when the cutting angle is 52°, the cutting force is the smallest, and the cutting angle is optimum. Thus, the prediction of frozen soil mechanical properties on the cutting process by this model is conducive to selecting machinery equipment in the field. 相似文献
12.
Temperature and moisture variations were experimentally investigated for the subgrade of the Astana-Burabai Highway, located in the northern region of Kazakhstan.Temperature and moisture were measured by means of specially manufactured sensors,including an element for temperature measurement based on the effect of thermal resistance and an element for moisture measurement through diamagnetic permeability.It was determined that the long-term average depth of frost penetration was 237 cm.In the upper part of the subgrade with 1 m of thickness,the average duration of a frozen condition decreases toward the bottom from 131 days to 117 days,with an average rate of 0.133 day/cm.The unfrozen water content decreases with the negative temperature reduction.In the case of high values of initial moisture (12%~22%),the unfrozen water content does not depend on the initial moisture;and it decreases under the power law,with reduction of negative temperature.In the case of the lowest values of moisture (9%~12%),the unfrozen water content depends also on negative temperature;but its values are considerably lower. 相似文献
13.
《Norsk geografisk tidsskrift. Norwegian journal of geography》2012,66(4):241-244
In the major physiographic divisions of the north-east of European Russia, temperatures in the cryolithozone and the active/seasonally frozen layer were monitored during the period 1970 to 1995. Active layer depths increased on average by 11% to 15%, whereas the depths of the seasonally frozen layer decreased by 19% to 40%. The largest positive temperature increments, up to 1.2C, were characteristic for the piedmont and basement plains. Lacustrine-alluvial lowlands demonstrated oppositely directed temperature trends depending on a landform. Numerous sites with ongoing permafrost formation demonstrated negative temperature increments varying from 0.1C to 2.0C. 相似文献
14.
Alexander Isakov 《寒旱区科学》2013,5(4):0353-0362
The main reasons for a breach of trouble-free operation of the subgrade are the different kinds of deformation, such as train load impact on
subgrade surface, loss of stability to subgrade slope, weight of embankment on the base, and partial or complete failure of the railway track
due to frost heaving. This paper gives a summary of deformation analysis methods being developed in Russia to estimate the operating conditions
of the railway subgrade. 相似文献
15.
V. G. Kondratiev 《寒旱区科学》2013,5(4):0377-0386
The history of railway and highway construction in permafrost zones in Russia, the United States, Canada, and China spans more
than 110 years. Nonetheless, no railway track or highway has yet been built in such area that is impervious to deformation caused
by subsidence resulting from the thawing of ice-rich subgrade soils. This paper presents data on the roadbed states of the Transbaikalian
and the Baikal-Amur Railways as well as the Russian "AMUR" Chita-Khabarovsk Highway. It also discusses the feasibility
of roadbed stability maintenance using methods based on the reduction of the mean annual ground temperature and roadbed
preservation in a permafrost state by means of the natural cooling and heating factors ratio regulation resulting in a reduction of the
heat generation in the roadbed and the adjoining area accompanied by an increase of heat consumption with help of the
sun-precipitation protective sheds (awnings), rock covers, dolomite powder (reflective paint), cooling tube and thermosyphons as
well as tower supports and corrugated pipe culverts stability. 相似文献
16.
According to the technical characteristics of short fixed wheelbase of a high-speed carriage, a subgrade-track integrated space mechanical response analysis model is proposed for trains under the action of biaxial load after the comparison of the stress distribution characteristics of the ballast track subgrade bed structures for high-speed railway under the action of uniaxial load and biaxial load. The loading threshold value (high-cycle long-term dynamic strength) under the circumstance where the cumulative deformation of subgrade structure gradually develops and finally reaches the convergent state, and its relationship with the foundation coefficient K30 were deduced, based on the characteristics of cumulative deformation evolution obtained from the unit structure filling model test under the action of cyclic loading. In view of structure stability and frost resistance requirements of the railway subgrade in cold regions, technical conditions to maintain good service performance of subgrade structure of high-speed railway ballasted track are discussed and analyzed. Study results show that the additive effect manifests itself obviously for railway train bogies under the action of biaxial load than uniaxial load, which has a significant dynamic effect on the subgrade bed bottom and a slight effect on the surface layer. Thus, the adoption of a biaxial load model in the design of a high-speed railway subgrade accurately reflects the vehicle load. Pursuant to the structure design principle, the design method of the subgrade structure of high-speed railway ballasted track is proposed to meet the technical requirements such as structural strength, bearing stiffness and high-cyclic and long-term stability. Technical indicators are obtained for the variation of thickness of the surface layer of reinforced subgrade bed in the double-layer subgrade mode along with the change of K30 at the subgrade bed bottom. The double-layer structure mode of "closure on the upper layer and drainage on the lower layer" was proposed in order to meet the waterproofing and drainage requirements of the upper layer of the subgrade bed in cold regions. A dense-framework graded gravel filler with weak water permeability at a coefficient of 10-4 cm/s is used on the upper layer and the void-framework graded gravel filler at the water permeability coefficient of 10-2 cm/s is adopted on the lower layer. 相似文献
17.
This paper aims to determine the optimal fines content of coarse-grained soil required to simultaneously achieve weaker frost susceptibility and better bearing capacity. We studied the frost susceptibility and strength properties of coarse-grained soil by means of frost heaving tests and static triaxial tests, and the results are as follows:(1) the freezing temperature of coarse-grained soil decreased gradually and then leveled off with incremental increases in the percent content of fines; (2) the fines content proved to be an important factor influencing the frost heave susceptibility and strength properties of coarse-grained soil. With incremental increases in the percent content of fines, the frost heave ratio increased gradually and the cohesion function of fines effectively enhanced the shear strength of coarse-grained soil before freeze-thaw, but the frost susceptibility of fines weakened the shear strength of coarse-grained soil after freeze-thaw; (3) with increasing numbers of freeze-thaw cycles,the shear strength of coarse-grained soil decreased and then stabilized after the ninth freeze-thaw cycle, and therefore the mechanical indexes of the ninth freeze-thaw cycle are recommended for the engineering design values; and (4) considering frost susceptibility and strength properties as a whole, the optimal fines content of 5% is recommended for railway subgrade coarse-grained soil fillings in frozen regions. 相似文献
18.
The developed vertical coupling model of Vehicle-Track-Subgrade which considered subgrade layer vibration is present-ed. The equations of motion for the ballast, top and bottom subgrade layers are pres... 相似文献
19.
Dynamic performance of insulation is one of the key parameters during the insulation application for high-speed railway subgrade. This paper conducted laboratory and field tests for the materials and dynamic load,especially for thermal performance, elastic deformation, and accumulated deformation of insulation materials.Experiment results show that mechanical properties of insulation layer structure are stable, which satisfies the requirements of the high speed railway. 相似文献
20.
采用哈尔滨市1989,2001,2007年Landsat TM遥感影像资料,利用单窗算法对地面温度进行反演,分析哈尔滨市热场的分布情况,并与20世纪90年代地形图结合来分析道路系统间的温度情况及其与城市热岛的关系。结果表明:铁路和公路温度差异显著且处于不同温度区的铁路温度也有显著的差异;铁路沿线地区热岛效应比较显著,铁路能使周围一定区域温度升高;公路系统作为一种特殊的廊道系统,对城市热岛有一定的阻隔、减缓作用;哈尔滨市铁路对热岛的影响范围不超过300 m,公路对城市热岛的降温作用最大值不超过0.4℃,在120 m以外降低作用很小或没有;绿化率的不同也影响道路对城市热岛的作用效果。 相似文献