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1.
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   

2.
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   

3.
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   

4.
陈同庆  金昌宁 《中国沙漠》2008,28(5):855-859
在中国沙漠地区选取典型路段,对风积沙路基进行强度测定。通过现场承载板试验,并分析已有的各种资料,发现野外实测的风积沙路基回弹模量普遍较高,明显高于现行有关规范推荐的砂性土或土质砂的路基回弹模量建议值,高出部分多在30%以上,已经明显地对路基路面的结构设计产生了不利影响。在此基础上,为能充分利用风积沙的强度特性,降低沙漠公路造价,通过进一步分析,提出了中国各主要沙漠地区及不同等级公路的风积沙路基回弹模量设计值。  相似文献   

5.
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   

6.
Rocks used as construction aggregate in temperate climates deteriorate to differing degrees because of repeated freezing and thawing. The magnitude of the deterioration depends on the rock's properties. Aggregate, including crushed carbonate rock, is required to have minimum geotechnical qualities before it can be used in asphalt and concrete. In order to reduce chances of premature and expensive repairs, extensive freeze-thaw tests are conducted on potential construction rocks. These tests typically involve 300 freeze-thaw cycles and can take four to five months to complete. Less time consuming tests that (1) predict durability as well as the extended freeze-thaw test or that (2) reduce the number of rocks subject to the extended test, could save considerable amounts of money. Here we use a probabilistic neural network to try and predict durability as determined by the freeze-thaw test using four rock properties measured on 843 limestone samples from the Kansas Department of Transportation. Modified freeze-thaw tests and less time consuming specific gravity (dry), specific gravity (saturated), and modified absorption tests were conducted on each sample. Durability factors of 95 or more as determined from the extensive freeze-thaw tests are viewed as acceptable—rocks with values below 95 are rejected. If only the modified freeze-thaw test is used to predict which rocks are acceptable, about 45% are misclassified. When 421 randomly selected samples and all four standardized and scaled variables were used to train aprobabilistic neural network, the rate of misclassification of 422 independent validation samples dropped to 28%. The network was trained so that each class (group) and each variable had its own coefficient (sigma). In an attempt to reduce errors further, an additional class was added to the training data to predict durability values greater than 84 and less than 98, resulting in only 11% of the samples misclassified. About 43% of the test data was classed by the neural net into the middle group—these rocks should be subject to full freeze-thaw tests. Thus, use of the probabilistic neural network would meanthat the extended test would only need be applied to 43% of the samples, and 11% of the rocks classed as acceptable would fail early.  相似文献   

7.
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   

8.
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   

9.
The freeze-thaw cycling process considerably changes the composition,structure,and properties of soils.Since the grain size is the most important factor in determining soil characteristics,our current research primarily aims to investigate dynamic changes of the soil fraction when exposed to freeze-thaw conditions.We observed two series of Moscow morainic clayey specimens(g QmII):(I) the original series,and(II) the remolded series.We subjected each series of soil specimens to different frequencies of freeze-thaw cycles(3,6,20,and 40 cycles),and we used granulometric tests to analyze both series before and after exposure to freeze-thaw conditions.As a result of our experiments,the granulometric compositions tended to be distributed evenly after 40 freeze-thaw processes(i.e.,content of fraction for 0.1–0.05 mm was increased after 40 freeze-thaw cycles) because the division of coarse grains and the aggregation of fine grains were synchronized during the freeze-thaw process.The soil grains in both series changed bi-directionally.In the original series,changes of the sand grains were conjugated with the clay grains,and in the remolded series,changes of the sand grains were conjugated with the silt grains,because potential energy difference caused the division and aggregation processes to relate to the counteraction process.The even distribution of soil grain size indicated the state of equilibrium or balance.The granulometric compositions were altered the most during the sixth freeze-thaw cycle,because the coefficient of the intensity variation of the grain fineness(Kvar) had its maximum value at that time.  相似文献   

10.
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   

11.
In order to determine the changing rule of long-term frozen soil strength and elucidate the connection between long-term strength and soil physical properties,frozen loess was subjected to 4,6,8,10,and 50 freeze-thaw cycles,under closed-state conditions in a constant-temperature box.The frozen samples were tested on a spherical template indenter,and the results show that under the effect of repeated freeze-thaw cycles,the long-term strength of frozen loess decreased; changes in the mechanical property indices were highly unstable during the first 10 cycles; the soil strength and density were the greatest at the eighth cycle while the void ratio was the smallest; and after eight cycles all of the indices had less fluctuation and certain rising or falling tendencies.By converting the number of freeze-thaw cycles into elapsed time in the tests,three different forecasting methods of long-term soil strength could be assessed and the soil equivalent cohesive force after 10 years,20 years,or 30 years could be estimated.  相似文献   

12.
Seasonally frozen soil is a four-phase material and its physical-mechanical properties are more complex compared to the unfrozen soil. Its physical properties changes during the freeze-thaw process; repeated freeze-thaw cycles change the characteristics of soil, which can render the soil from an unstable state to a new dynamic equilibrium state. The freezing process changes the structure coupled between the soil particle arrangements, which will change the mechanical properties of the soil. The method of significance and interaction between different factors should be considered to measure the influence on the properties of soil under freeze-thaw cycles.  相似文献   

13.
Usually, the collapsible loess widely distributed across the world can serve as a type of foundation soil that meets its strength requirement after dense compaction and elimination of collapsibility. However, many problems such as cracks and differential settlement still occur in loess roads in the seasonally frozen ground regions after several years of operation. Many studies have demonstrated that these secondary or multiple collapses primarily result from the repeatedfreezing-thawing, wetting-drying, and salinization-desalinization cycles. Therefore, we conducted a research program to (1) monitor the in-situ ground temperatures and water content in certain loess roads to understand their changes, (2) study the effects of freezing-thawing, wetting-drying, and salinization-desalinization cycles on geotechnical properties and micro-fabrics of compacted loess in the laboratory, and (3) develop mitigative measures and examine their engineered effectiveness, i.e., their thermal insulating and water-proofing effects in field and laboratory tests. Our results and advances are reviewed and some further research needs are proposed. These findings more clearly explain the processes and mechanisms of secondary and multiple collapse of loess roads. We also offer references for furtherstudy of the weakening mechanisms of similar structural soils.  相似文献   

14.
Natural aggregate is vital to the construction industry. Although natural aggregate is a high volume/low value commodity that is abundant, new sources are becoming increasingly difficult to find and develop because of rigid industry specifications, political considerations, development and transportation costs, and environmental concerns. There are two primary sources of natural aggregate: (1) exposed or near-surface bedrock that can be crushed, and (2) deposits of sand and gravel. Remote sensing and airborne geophysics detect surface and near-surface phenomena, and may be useful for detecting and mapping potential aggregate sources; however, before a methodology for applying these techniques can be developed, it is necessary to understand the type, distribution, physical properties, and characteristics of natural aggregate deposits.The distribution of potential aggregate sources is closely tied to local geologic history. Conventional exploration for natural aggregate deposits has been largely a ground-based operation, although aerial photographs and topographic maps have been extensively used to target possible deposits. Today, the exploration process also considers factors such as the availability of the land, space and water supply for processing, political and environmental factors, and distance from the market; exploration and planning cannot be separated.There are many physical properties and characteristics by which to judge aggregate material for specific applications; most of these properties and characteristics pertain only to individual aggregate particles. The application of remote sensing and airborne geophysical measurements to detecting and mapping potential aggregate sources, however, is based on intrinsic bulk physical properties and extrinsic characteristics of the deposits that can be directly measured, mathematically derived from measurement, or interpreted with remote sensing and geophysical data. On the cover: Northward view of alluvial fans along San Luis Valley, southcentral colorado. This image was created in the U.S. Geological Survey (USGS) Remote Sensing laboratory by digitally draping SPOT panchromatic satellite data resampled to 30 meters pixels resolution over the 124,000 USGS DEM of the Bonanza, Whle Hill, Bushnell Peak, Graveyard Guich, Klondike Mine, and Villa Grove quadrangles.  相似文献   

15.
The impact of snow cover on seasonal ground frost and freeze-thaw processes is not yet fully understood. The authors therefore examined how snow cover affects seasonal ground frost in a coastal setting in northern Sweden. Air and soil temperatures were recorded in a paired-plot experiment, both with and without snow cover, during the frost season 2012–2013. The frequency, duration, and intensity of the freeze-thaw cycles during the frost season were calculated. The results showed that the freeze-thaw frequency was 57% higher at the soil surface and the intensity 10 °C colder in the spring of 2013, when the ground lacked snow cover. Furthermore, the duration of the seasonal freeze-thaw cycle was 30 days longer on average in cases where there was natural snow accumulation. The correlation between air and ground surface temperatures weakened with increased snow-cover depth. The authors conclude that continued increases in air temperature and decreases in snow in coastal northern Sweden might alter freeze-thaw cycles and thus affect natural and human systems such as geomorphology, ecology, spatial planning, transport, and forestry.  相似文献   

16.
As part of a multidisciplinary investigation of the Misiano archaeological site, pollen and nonsiliceous algae were recovered from a 262 cm core from Gegoka Lake, Lake County, Minnesota. The palynomorph assemblage from Gegoka Lake records changes in local and regional vegetational and lake productivity over the past 10 000 years. Pollen spectra indicate that vegetation progressed from a shrub parkland/open conifer forest, to a spruce-pine forest, to a mixed conifer-hardwood forest. Pinus banksiana/resinosa is replaced by Pinus strobus about 7000 years ago. A small rise in Gramineae in the upper 17.5 cm of the core is attributed to the expansion of wild rice (Zizania aquatica) in Gegoka Lake. Four cycles of nutrient enrichment are indicated by the Pediastrum and Scenedesmus maxima in the nonsiliceous algae record. Oscillations in the nonsiliceous algae abundance probably result from changing environmental and/or limnologic conditions. The decline in nonsiliceous algae in the upper 57.5 cm of the core suggests that there has been an apparent shift to more nutrient poor conditions in Gegoka Lake in the recent past.This is the 17th in a series of papers published in this special AMQUA issue. These papers were presented at the 1994 meeting of the American Quaternary Association held 19–22 June, 1994, at the University of Minnesota, Minneapolis, Minnesota, USA. Dr Linda C. K. Shane served as guest editor for these papers.  相似文献   

17.
土壤冻融交替是陆地表层极其重要的物理过程,土壤冻融状态的频繁变化对地气能量交换、地表径流、植被生长、生态系统及土壤碳氮循环等均具有重要的影响。本文基于1981—2019年ERA5-LAND逐小时土壤温度数据,借助GIS空间分析功能,利用Python编程处理分析了中国东北地区近地表土壤冻融状态的时空变化特征。结果表明：从不同冻融状态起始日期的空间分布来看,近地表不同阶段的起始日期主要受纬度和地形的影响,具有明显的纬度地带性和垂直地带性。春季冻融过渡期和完全融化期的起始日期由东南向西北均呈逐渐推迟趋势,而秋季冻融过渡期与完全冻结期起始日期则由东南向西北随纬度升高越来越早。就不同冻融状态发生天数的空间分布而言,研究区南部春季冻融过渡期发生天数多于北部,西部多于东部,年均发生天数均在30 d以内;秋季发生冻融的天数空间差异不大,研究区一半以上的地区年均发生天数在10 d以内。完全融化期发生天数最多,从东南向西北呈逐渐减少趋势,年均发生天数主要介于150~240 d之间;完全冻结期发生天数则由南向北日益增多,其空间分布表现为一向南开口的簸箕形,各地年均发生天数集中于90~180 d之间。从时间变化趋势来看,近年来春季冻融过渡期起始日期以提前趋势为主,而秋季冻融过渡期起始日期总体表现为延后,致使完全融化期发生天数以增加趋势为主,年均变化速度高达0.2 d/a;大兴安岭以西、呼伦贝尔高原以北地区及辽河平原春季冻融过渡期发生天数呈减少趋势,其他地区为增加趋势;大兴安岭以西地区、呼伦贝尔高原以北地区完全融化期起始日期明显提前;松嫩平原和长白山区秋季冻融过渡期起始日期推迟显著,发生天数的变化趋势呈北增南减的空间分异特征;不同地区完全冻结期起始日期的变化趋势差异显著,中部广大的平原区呈不显著的推迟趋势,而大、小兴安岭、长白山、辽东半岛和辽西丘陵则提前进入完全冻结状态;研究区完全冻结期发生天数呈减少趋势,研究区中部的季节冻土区完全冻结期明显变短,年均减少速度大于0.2 d/a。  相似文献   

18.
Intense freezing and thawing actions occur in the Qinghai–Tibet Plateau because of its high elevation and cold temperature. The plateau's unique environment makes it easy to generate wind erosion under dry, windy weather conditions, resulting in the emergence of desertification. As a major form of freeze–thaw erosion, freeze–thaw and wind erosion is displayed prominently on the Qinghai–Tibet Plateau. Therefore, in this study, soil samples were collected from the surface of the plateau to undergo freeze–thaw and wind erosion simulation experiments. Results show that wind erosion strength increases with an increasing number of freeze–thaw cycles, water content in the freezing–thawing process, and the difference in freeze–thaw temperatures. Therefore, in the conditions of water participation, the main reason for the freeze–thaw and wind erosion in the Qinghai–Tibet Plateau is the damage to the soil structure by repeated, fierce freeze–thaw actions, and the sand-bearing wind is the main driving force for this process. The research results have theoretical significance for exploring the formation mechanism of freeze–thaw and wind erosion in the Qinghai–Tibet Plateau, and provide a scientific basis for freeze–thaw desertification control in the plateau.  相似文献   

19.
The acquisition of a freezing remanent magnetization (FRM) has been studied in controlled magnetic and thermal environments by successive freezing and thawing (−18 to +20°C) of samples of natural sediments from a frost polygon near Ny Ålesund, Spitsbergen. Successive freeze-thaw cycles cause a significant decrease in the intensity of the initially induced shock remanent magnetization (SRM), associated with directional trends towards the ambient magnetic field direction during the freezing phase. A slow increase in intensity commences after seven to 10 freeze-thaw cycles. The acquisition of a FRM in samples carrying an isothermal remanent magnetization shows a significantly smaller reduction in intensity and only minor directional variations. This result indicates that only a fraction of the magnetic grains in a natural sediment contributes to the natural remanent magnetization. Insignificant changes in lengths and directions of the principal susceptibility ellipsoid axes also indicate that magnetic fabric and remanent magnetization are carried by partly different populations of magnetic grains.
The acquisition of a FRM in nature has yet to be explored. If such a process is confirmed, however, it has the potential for obtaining age estimates of ancient thaw depths and for providing insights into material transport processes in frost polygons.  相似文献   

20.
土地利用方式对土壤有机碳和团聚体组分特征的影响   总被引：4，自引：0，他引：4  
以广东省内第四纪红色黏土、玄武岩和花岗岩母质发育的土壤为研究对象,采集不同土地利用方式（水田、旱地、林地、果园/草地）下表层（0~15 cm）和亚表层（15~30 cm）土壤,研究土壤有机碳及其组分（腐殖质碳、易氧化有机碳）、土壤团聚体及其稳定性,分析土壤有机碳及其组分与土壤团聚体及其稳定性之间的相互关系。结果表明：土地利用类型、成土母质等影响土壤有机碳及其组分。3种母质发育的土壤中,各腐殖质组分占有机碳的比例是胡敏酸碳（HAC）＜富里酸碳（FAC）＜胡敏素碳（HMC）,第四纪红色黏土母质发育土壤腐殖酸碳（HAC＋FAC）以草地最高、水田最低;玄武岩、花岗岩母质发育土壤腐殖酸碳以果园最高。土壤中易氧化有机碳所占比例均高于惰性态,第四纪红色黏土母质发育土壤易氧化有机碳占有机碳比例以草地最高、旱地最低;玄武岩、花岗岩为果园最高、林地最低。3种母质发育土壤团聚体（湿筛）主要以＜0.25 mm微团聚体为主,表层土壤＞0.25 mm团聚体所占比例、团聚体平均重量直径（MWD）、团聚体破坏率（PAD）大于亚表层。土壤有机碳各组分均随着有机碳质量分数的增加而增加,＞0.25 mm团聚体质量分数和团聚体MWD随着土壤有机碳及其组分质量分数的增加而增大;PAD随着土壤易氧化碳组分质量分数增加而降低,易氧化有机碳组分有利于土壤中形成较大的团聚体,并增加团聚体水稳性。  相似文献   

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