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1.
Finiteelement simulations are increasingly providing a versatile environment for this topic. In this study, a two-dimensional finite element analysis is conducted to predict the deformation of highembankment in Bazhun heavy-haul railway, China. A recently developed nonlinear softening-type constitutive model is utilized to model the behavior of subgrade filling materials subjected to freeze-thaw cycles. For the convenience of practical application, the dynamic loading induced by a vehicle is treated as a quasi-static axle load. The deformation of this embankmentwith different moisture content under freeze-thaw cycles is compared. The results show that when subjected to the first freeze-thaw cycle, the embankmentexperienced significant deformation variations. Maximum deformation was usually achieved after the embankment with optimum moisture content experienced six freeze-thaw cycles, however, the embankment with moisture content of 8.0% and 9.5% deforms continuously even after experiencing almost ten freeze-thaw cycles. Overall, this study provides a simple nonlinear finite element approach for calculating the deformation of the embankmentinchanging climate conditions. 相似文献
2.
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
3.
This paper reports on the dynamic response of highway subgrade under moving heavy truck in cold regions. Numerical simulations are
performed in two stages. In the first stage, the moving heavy truck vibration, induced by road roughness, is calculated through a
three-dimensional dynamic interaction model of heavy truck-pavement-subgrade, and the time-histories of nodal loads on the top of the
base are calculated through this model. In the second stage, a two-dimensional dynamic finite element model of the base-subgrade-ground
system is formulated, using the calculated nodal loads from the first stage as input. The dynamic response of the subgrade is validated by field
measurements, and the effects of truck type, axle loading, running speed, and road roughness on the vertical dynamic stress in the unfrozen
period and the spring thawing period are analyzed and discussed. 相似文献
4.
Frost heaving is a well-known phenomenon in cold regions, which may occur in wet clayey grounds during winter. Railway track upheaval occurring in cold regions during the winter is generally understood as frost heaving in the subgrade layer. However, it has been confirmed that upheaval due to frost heaving sometimes occurs in the ballast layer. This understanding has been observed in active railways in northern Japan. The samples collected from ballast and subgrade layers have been examined for frost heave susceptibilities and confirmed that ballast layers which contain fines may heave. 相似文献
5.
Regarding the freezing damage of high-grade highway subgrade in seasonally frozen area,the thesis explores the effect on the dynamic behavior of subgrade soil under freeze–thaw cycles and draws the change law of parameters(including dynamic strength,dynamic cohesion,and internal friction angle;and dynamic elastic modulus)of high-grade highway-subgrade soil with the number of freeze–thaw cycles.It aims to provide the reference for operation and maintenance of a high-grade highway.Conclusions:(1)Dynamic strength tends to decline evidently after freeze–thaw cycles,with 60%~70%decline after three cycles,and remains stable after five to seven cycles.(2)With the number of freeze–thaw cycles increasing,the internal friction angle fluctuates within a certain range without an obvious change law,only presenting the tendency of dropping off.The dynamic cohesion declines obviously,about 20%~40%after seven freeze–thaw cycles,and then tends to be stable.(3)With the number of freeze-thaw cycles increasing,the dynamic elastic modulus and maximum dynamic elastic modulus are inclined to decrease distinctly.After five freeze–thaw cycles,the former declines 30%~40%and then remains stable.Meanwhile,the latter falls 20%~40%. 相似文献
6.
The uneven frost heave of frost-susceptible subgrade soil causes track irregularity, which highly enhances train vibration and affects the comfort and safety of railway transportation. This paper presents a coupled thermo-hydro-mechanical (THM) analysis for the freezing behavior of railway located above a box culvert. The vertical acceleration of the vehicle, an indicator of riding comfort, is predicted through a vehicle dynamic model. The results reveal that the existence of a box culvert changes the subgrade thermal pattern, leading to a deeper frost penetration depth. The frost heave amount above the box culvert is larger than the adjacent section, resulting in uneven track structure upheave and track irregularity. This frost-induced track irregularity highly affects train vibration. 相似文献
7.
To investigate the static and dynamic resilient modulus of fine soil, and adapting to the new design code and maintenance system of highway subgrade in China, a series of static and dynamic tests were carried out according to the standard laboratory test methods (JTG E40-2007 and JTG D30-2015, respectively). The effects of initial water content, compactness and freeze-thaw cycles on the static and dynamic resilient moduli of fine soil were investigated and analyzed. Experimental test results show that with increasing water content, dry density and freeze-thaw cycles, the static moduli reduces about 10.2%~40.0%, 14.4%~45.5%, and 24.0%~50.3%, and dynamic moduli reduces about 10.9%~90.8%, 2.5%~38.4%, and 0.0%~46.0%, respectively. Then, the empirical mathematical relationship between static and dynamic resilient moduli was established under different water content, dry density and freeze-thaw cycles. The investigation results can be used to determine the dynamic modulus of fine soil by widely used static modulus, which could meet the requirement of adopting dynamic modulus index in new specification. 相似文献
8.
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
9.
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
10.
This paper presents the results of field and laboratory tests of railway ballast.Field tests were aimed to study vibrational acceleration of ballast particles and ballast layer stressed state in terms of train traffic with heavy axle loads.The test results are vibrational acceleration and stress values distribution in ballast layer and experimental relationships of vertical and horizontal vibroaccelerations damping in terms of train operation with axle load up to 300 kN.Laboratory stabilometer tests were directed to study the change of ballast strength properties due to vibrodynamic impact and shows that for dynamic loading with 10,25,55 Hz frequencies vibrodynamic impact influences strength properties insignificantly and coincides with the accuracy of test equipment.Stated test results provide references for calculation of ballast and sub-ballast bearing capacity. 相似文献
11.
冻融条件下土壤中水盐运移规律模拟研究 总被引：16，自引：0，他引：16
冻融作用是土壤盐碱化独特的形成机制,冻融条件下土壤中盐分迁移是水分对流、浓度梯度、温度梯度、不同溶质、土壤结构及质地等因素作用下的综合结果,温度是导致土壤中水分与盐分迁移的驱动力。在土壤冻融过程中,水分和盐分的两次迁移过程构成了特殊的水盐运动规律。在冻融过程中,土壤剖面结构发生变异,形成冻结层、似冻结层和非冻结层。冻结带土水势降低导致水分不断向冻层迁移,冻结缘以下的盐分同步向上运移,整个冻层的土壤含盐量明显增加;在融化过程中,随着地表蒸发逐渐强烈,使冻结过程中累积于冻结层中的盐分,转而向地表强烈聚集,使表层的盐分含量急剧上升。当冻结层未融通之前,尚未融化的冻层起到隔水的作用,不但阻止顶部融水向下层渗透,而且隔断了与下层水的联系。模拟实验结果充分证明了中国北方冻融区域土壤盐碱化的发生过程,为有效防治土壤盐碱化提供了理论依据。 相似文献
12.
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
13.
This article provides an overview of several previous studies that investigated the stiffness and strength performance of chemically stabilized roadway materials under winter conditions (freeze-thaw cycling). The objective of this research was to understand the behavior of different materials stabilized with different type of binders when they were subjected to freeze-thaw cycling. Nine different materials including natural soils (organic soil, clay, silt, sand, and road surface gravel), reclaimed pavement material, and recycled asphalt pavement stabilized with nine different binders (five different fly ashes, lime, cement, lime kiln dust, cement kiln dust) were discussed. This article investigated how the volume, resilient modulus and unconfined compressive strength of soils/materials stabilized with different binders change in response to freeze-thaw cycling. Overall, the review results indicate that the stiffness and strength of all stabilized materials decrease somewhat with freeze-thaw cycling. However, the reduced strength and stiffness of stabilized materials after freeze-thaw cycling was still higher than that of unstabilized-unfrozen original soils and materials. In addition, materials stabilized with cement kiln dust provided the best performance against freeze-thaw cycling. 相似文献
14.
Sergei Kudriavtcev Tatiana Valtsev Alexei Kazharskyi Elena Goncharov Iurii Berestianyi 《寒旱区科学》2013,5(4):0404-0407
The goal of a predictive thermotechnical calculation is to model the behavior of the top permafrost boundary under current
operational conditions as well as increasing average annual air temperatures that results in degradation of the permafrost
layer. Numerical modeling was used to assess the efficient application of construction measures to create sustainable operation
of the railroad. The numerical modeling was carried out in the programming complex FEM-models developed by
geotechnical engineers of St. Petersburg, Russia under Prof. V. M. Ulitsky’s guidance. The Termoground Program as a part
of the FEM-models enables the research of freezing, heaving and thawing in different design solutions. Research was
carried out in space resolution for a year cycle. The performed model has shown that the designing measures accepted for
permafrost protection from retreat in the subgrade support were generally effective. 相似文献
15.
In this paper, a variation series of snow cover and seasonal freeze-thaw layer from 1965 to 2004 on the Tibetan Plateau has been established by using the observation data from meteorological stations. The sliding T-test, M-K test and B-G algorithm are used to verify abrupt changes of snow cover and seasonal freeze-thaw layer in the Tibetan plateau. The results show that the snow cover has not undergone an abrupt change, but the seasonal freeze-thaw layer obviously witnessed a rapid degradation in 1987, with the frozen soil depth being reduced by about 15 cm. It is also found that when there is less snow in the plateau region, precipitation in South China and Southwest China increases. But when the frozen soil is deep, precipitation in most of China apparently decreases. Both snow cover and seasonal freeze-thaw layer on the plateau can be used to predict the summer precipitation in China. However, if the impacts of snow cover and seasonal freeze-thaw layer are used at the same time, the predictability of summer precipitation can be significantly improved. The significant correlation zone of snow is located in middle reaches of the Yangtze River covering the Hexi Corridor and northeastern Inner Mongolia, and the seasonal freeze-thaw layer exists in Mt. Nanling, northern Shannxi and northwestern part of North China. The significant correlation zone of simultaneous impacts of snow cover and seasonal freeze-thaw layer is larger than that of either snow cover or seasonal freeze-thaw layer. There are three significant correlation zones extending from north to south: the north zone spreads from Mt. Daxinganling to the Hexi Corridor, crossing northern Mt. Taihang and northern Shannxi; the central zone covers middle and lower reaches of the Yangtze River; and the south zone extends from Mt. Wuyi to Yunnan and Guizhou Plateau through Mt. Nanling. 相似文献
16.
Three stages of complex technological monitoring for the increase of high-temperature-permafrost soil bearing capacity are described. The feasibility of process monitoring to improve the targeted strength properties of subgrade bases on frozen soils is demonstrated. The rationale for the necessity of predictive modeling of freeze-thaw actions during the subgrade construction period is provided. 相似文献
17.
青藏铁路沙害及其防治研究进展 总被引：2，自引：2，他引：0
青藏铁路是中国乃至世界上海拔最高、穿越沙漠冻土的高原铁路。建成以来风沙危害日趋严重,成为危及铁路安全运营的一大隐患,因此,沿线的风沙防治一直备受关注。由于青藏高原风力强劲,沙物质丰富加上人类活动的影响,铁路沙害呈现出分布相对集中,冻融与风力、水力复合侵蚀,不断发展并持续累积,风沙活动稳定性差等特点。沙害分为路基风蚀、道床积沙、磨蚀等类型。累计有轻度、中度、严重沙害路段440 km,主要分布在锡铁山、伏沙梁、红梁河、秀水河-北麓河、沱沱河、通天河、扎加藏布、错那湖等8个路段。目前铁路沙害防治以机械措施为主,在设置初期有一定的防沙效果,但随着时间的推移,最终会被积沙埋没而失效。因此,青藏铁路防沙应以生物措施（恢复植被）为主,机械措施为辅。 相似文献
18.
Frost heave is an upward swelling of soil during cryogenic conditions in cold regions. It is caused by the accumulation of ice crystals in subgrade soil, which grow upwards when freezing temperatures penetrate into the subgrade. This study establishes the allowable soil subgrade frost heave based on the roughness standard of asphalt pavement in China, and aims to balance the pavement design and frost heave resistance of subgrades in cold regions. We formulated a mechanical model of pavement supported by the boundary conditions of differential frost heave, based on the elastic layered system theory. The differential soil subgrade frost heave was modeled as a sinusoidal function, and the allowable frost heave and the roughness index were modeled as the displacement boundaries for the top and bottom of the pavement structure. Then the allowable frost heave was back-calculated according to the roughness standard. Numerical results show that the allowable frost heave depends on the pavement structure, material properties, the highway grade, and other factors. In order to ensure that the actual soil subgrade frost heave is lower than the allowable frost heave, pavement structures and materials need to be selected and designed carefully. The numerical method proposed here can be applied to establish the frost heave resistance of subgrade when the pavement structure and materials are determined. 相似文献
19.
The active-layer soils overlying the permafrost are the most thermodynamically active zone of rock or soil and play important roles in the earth-atmosphere energy system. The processes of thawing and freezing and their associated complex hydrothermal coupling can significantly affect variation in mean annual temperatures and the formation of ground ice in permafrost regions. Using soil-temperature and-moisture data obtained from the active layer between September 2011 and October 2014 in the permafrost region of the Nanweng'he River in the Da Xing'anling Mountains, the freeze-thaw characteristics of the permafrost were studied. Based on analysis of ground-temperature variation and hydrothermal transport characteristics, the thawing and freezing processes of the active layer were divided into three stages:(1) autumn-winter freezing,(2) winter freeze-up, and(3) spring-summer thawing. Variations in the soil temperature and moisture were analyzed during each stage of the freeze-thaw process, and the effects of the soil moisture and ground vegetation on the freeze-thaw are discussed in this paper. The study's results show that thawing in the active layer was unidirectional, while the ground freezing was bidirectional(upward from the bottom of the active layer and downward from the ground surface).During the annual freeze-thaw cycle, the migration of soil moisture had different characteristics at different stages. In general, during a freezing-thawing cycle, the soil-water molecules migrate downward, i.e., soil moisture transports from the entire active layer to the upper limit of the permafrost. In the meantime, freeze-thaw in the active layer can be significantly affected by the soil-moisture content and vegetation. 相似文献
20.
The sufficient bond between concrete and rock is an important prerequisite to ensure the effect of shotcrete support. However, in cold regions engineering protection system, the bond condition of rock and concrete surface is easily affected by freeze-thaw cycles, resulting in interface damage, debonding and even supporting failure. Understanding the micromechanisms of the damage and debonding of the rock-concrete interface is essential for improving the interface protection.Therefore, the micromorphology, micromechanical properties, and microdebonding evolution of the sandstone-concrete interface transition zone(ITZ) under varying freeze-thaw cycles(0, 5, 10, 15, 20) were studied using scanning electron microscope, stereoscopic microscope, and nano-indentation. Furthermore, the distribution range and evolution process of ITZ affected by freeze-thaw cycles were defined. Major findings of this study are as follows:(1) The microdamage evolution law of the ITZ under increasing freeze-thaw cycles is clarified, and the relationship between the number of cracks in the ITZ and freeze-thaw cycles is established;(2) As the number of freeze-thaw cycles increases, the ITZ's micromechanical strength decreases, and its development width tends to increase;(3) The damage and debonding evolution mechanisms of sandstone-concrete ITZ under freeze-thaw cycles is revealed, and its micromechanical evolution model induced by freeze-thaw cycles is proposed. 相似文献