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1.
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
2.
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
3.
Horizontal soil column method was used to determine the horizontal diffusion rate of sandy loam, loam and clay loam under the same bulk density. The results showed that the migration rates of different lithological wet fronts were different. The sandy loam had the fastest migration rate, the loam followed, and the clay loam was the slowest, but the law of change is the same among the three lithologies. The volumetric water content affects the change of Boltzmann parameter λ. When the volumetric water content is between 0.35-0.45 cm~3/cm~3, λ approaches stability. When the volumetric water content is less than 0.35 cm~3/cm~3, the λ value decreases rapidly with the decrease of water content. The water diffusion rate is related to the volumetric water content and particle size. The greater the moisture content is, the greater the diffusion rate will be. The larger the particle size, the larger the diffusion rate. The diffusivity of sandy loam is 10-30 times larger than that of loam and clay loam. The relationship between water content and diffusion rate is in accordance with the exponential function. 相似文献
4.
Frozen soil is generally regarded as a strongly rheological geomaterial. The strength attenuation of frozen soil is an important inducement for disease and instability in subgrade engineering, pile engineering and artificial freezing construction. Few efforts have been made to investigate the attenuation characteristics of strength envelope surface for frozen soil under complex stress states experimentally and theoretically. Considering this, at a temperature of -6 ℃, a series of triaxial stress relaxation tests under various confining pressures were carried out on the frozen subgrade soil specimens at strength points. The degeneration of strength parameters and stress attenuation process of frozen soil under complex stress states were systematically studied. The degradation law and mechanism of cohesion and internal friction angle are synchronously revealed in the stress relaxation process. Testing results indicate that the stress relaxation process of compacted frozen soil is significantly influenced by confining pressure. The stress relaxation ratio is increasing linearly with the rise of confining pressure if the confining pressure is beyond 1. 5 MPa. The anti-relaxation ability of frozen soil is greatly reduced during high confining pressure conditions:the stress relaxation ratio of frozen soil is only 41. 94% under 1. 5 MPa, but exceeds 90. 30% under 16 MPa. The strength of frozen soil attenuates linearly with time in the semi-logarithmic coordinate system. When the confining pressure is higher than 1. 5 MPa, the strength attenuation rate of frozen soil increases with the rise of confining pressure. As the development of stress relaxation of frozen soil, cohesion decreases linearly but internal friction angle increases linearly with time in the semi-logarithmic coordinate system. It manifested that the cementation in frozen soil shows evident rheological features and it is a key inducement for strength attenuation. Moreover, the attenuation law and value of cohesion in frozen soil which is measured by triaxial stress relaxation test are similar to the spherical template indenter test results. This may provide a new test method for obtaining the long-term strength and cohesion of frozen soil. On the basis of test results, the stress states of frozen soil in all stress relaxation curves at 12 relaxation durations were captured, and the rate-dependent variation characteristics of strength envelope in p-q stress space were analyzed in detail. Under high confining pressures, the strength envelope of frozen soil shows different geometric features as time goes on. In addition to the decline of level, the strength surface exhibits clockwise rotation with time, and the third stage sharply decreases at first and then becomes flat. Based on the analysis of characteristics of experimental strength surface and evolution law of strength parameters during the stress relaxation process, a rate-dependent strength theory for frozen soil considering the stress relaxation effect is established in this paper. © 2022 Science Press (China). All rights reserved. 相似文献
5.
A comprehensive grasp of the research status of tensile strength of frozen soil is the basis for further research. Firstly,the typical methods that can be used to test the tensile strength of frozen soil are introduced,and the test conditions,sample forms and stress mechanism of different test methods are described in detail. The advantages and disadvantages of typical tensile strength test methods are compared and listed. Secondly,the research work and shortcomings based on different test methods are summarized. Then,the latest research progress of the influence of temperature,water content,loading（deformation）rate,soil quality and sample size on the change law of frozen soil tensile strength is comprehensively analyzed. Finally,it is proposed to develop and improve the research method and system of frozen soil tensile strength,and increase the testing research of warm frozen soil tensile strength,so as to obtain the prospect of more accurately simulating the tensile failure behavior of frozen soil. It is pointed out that the internal cause of the formation of the tensile strength and the tensile failure mechanism of frozen soil should be thoroughly revealed by combining the research methods of microstructure and digital image technology of frozen soil. Based on the multi-factor test,a more perfect prediction method of frozen soil tensile strength is explored. Meanwhile,expand the in-situ test research on the tensile strength of frozen soil,and strengthen the parallel research ideas of indoor and outdoor double tracks. Through the analysis of the research status and development trend at home and abroad,it provides reference and guidance for the experimental study of frozen soil tensile strength,the improvement of theoretical model of frost heave,geotechnical engineering design in cold regions and artificial freezing reinforcement engineering. © 2022 Science Press (China). 相似文献
6.
Cryogenic structure (patterns made by ice inclusions) in seasonally frozen and permafrost-af-fected soils result from ice formation during freezing. Analysis of cryogenic structures in soils is essential to our understanding of the cryogenic processes in soils and to formulating land use management interpretations. When soils freeze, the freezing front moves downward and attracts water moving upward resulting in mainly horizontal lenticular ice formation. Platy and lenticular soil structures form between ice lenses in upper active layer. The reticular soil structure usually forms above the permafrost table caused by freeze-back of the permafrost. The upward freeze-back resulted in platy soil structure and the volume changes following the annual freeze-thaw cycle resulted in vertical cracks. The combined result is an ice-net formation with mineral soils embedded in the ice net. The upper permafrost layer that used to be a part of the active layer has an ice content exceeding 50% due to repeated freeze-thaw cycles over time. The mineral soils appear in blocks embedded in an ice matrix. The permafrost layer that never experienced the freeze-thaw cycle often consists of alternate layers of thin ice lens and frozen soils with extreme hard consistence and has relatively lower ice content than the ice-rich layer of the upper permafrost. Ice contents and thaw settling potentials associated with each cryogenic structure should be considered in engineering and land use interpretations. 相似文献
7.
Yang Xiao Minqiang Meng Ali Daouadji Qingsheng Chen ZhijunWu Xiang Jiang 《地学前缘(英文版)》2020,(2):375-388
Strength and deformation behaviors of rockfill materials,key factors for determining the stability of dams,pertain strongly to the grain crushing characteristics.In this study,single-particle crushing tests were carried out on rockfill materials with nominal particle diameters of 2.5 mm,5 mm and 10 mm to investigate the particle size effect on the single-particle strength and the relationship between the characteristic stress and probability of non-failure.Test data were found to be described by the Weibull distribution with the Weibull modulus of 3.24.Assemblies with uniform nominal grains were then subjected to one-dimensional compression tests at eight levels of vertical stress with a maximum of 100 MPa.The yield stress in one-dimensional compression tests increased with decreasing the particle size,which could be estimated from the single-particle crushing tests.The void ratio-vertical stress curve could be predicted by an exponential function.The particle size distribution curve increased obviously with applied stresses less than 16 MPa and gradually reached the ultimate fractal grading.The relative breakage index became constant with stress up to 64 MPa and was obtained from the ultimate grading at the fractal dimension(a?2:7).A hyperbolical function was also found useful for describing the relationship between the relative breakage index and input work during one-dimensional compression tests. 相似文献
8.
Using pore-solid fractal dimension to estimate residual LNAPLs saturation in sandy aquifers: A column experiment 
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下载免费PDF全文 The“tailing”effect caused by residual non-aqueous phase liquids(NAPLs)in porous aquifers is one of the frontiers in pollution hydrogeology research.Based on the current knowledge that the residual NAPLs is mainly controlled by the pore structure of soil,this study established a method for evaluating the residual saturation of NAPLs by investigating the fractal dimension of porous media.In this study,the soil column experiments of residual light NAPLs(LNAPLs)in sandy aquifer with different ratios of sands and soil were carried out,and the correlation between the fractal dimension of the medium,the residual of LNAPLs and the soil structure parameters are statistically analyzed,and its formation mechanism and main control factors are discussed.The results show that:Under our experimental condition:(1)the fractal dimension of the medium has a positive correlation with the residual saturation of NAPLs generally,and the optimal fitting function can be described by a quadratic model:SR=192.02 D2-890.73 D+1040.8;(2)the dominant formation mechanism is:Smaller pores in the medium is related to larger fractal dimension,which leads to higher residual saturation of NAPLs;stronger heterogeneity of the medium is related to larger fractal dimension,which also leads to higher residual saturation of NAPLs;(3)the micro capillary pores characterized by fine sand are the main controlling factors of the formation mechanism.It is concluded that both the theory and the method of using fractal dimension of the medium to evaluate the residual saturation of NAPLs are feasible.This study provides a new perspective for the research of“tailing”effect of NAPLs in porous media aquifer. 相似文献
9.
Beiluhe basin lies in a permafrost region where is located in the interior of Tibetan Plateau. Ecosystem in the area is subjected to the freeze-thaw process of the active tjaele,and there is conspicuous correlation between soil moisture（SM）and vegetation coverage. To retrieve the soil moisture content of Beiluhe basin with a total area of 2 037. 94 km2,a synergistic method,which combined improved water cloud model,Oh,Dubois and Topp model,was presented in this paper base on Sentinel-1A multi-polarization SAR and Landsat-8 time series images data. The accuracy was validated with the in-situ point SM data：Adjusted-R2 of the regression equation is 0. 6848,and RMSE is 0. 039 cm3·cm-3. The analysis of correlation among freeze-thaw process,SM and vegetation cover from macro watershed scale manifests：Vegetation coverage has a significant delayed effect on the freeze-thaw process of the active tjaele,that is,the higher vegetation coverage,the more lagging freeze-thaw time;These study results are basically consistent with predecessors in-situ observation data,verifying the feasibility of studying correlation among soil freeze-thaw process,SM,and vegetation coverage from the macro watershed scale based on Sentinel-1A annual time series data. © 2022 Science Press (China). 相似文献
10.
It is well known that the compressibility of crushable granular materials increases with the moisture content,due to the decrease of particle strength in a humid environment.An existing approach to take into account the effect of grain breakage in constitutive modeling consists in linking the evolution of the grain size distribution to the plastic work.But how the material humidity can affect this relationship is not clear,and experimental evidence is quite scarce.Based on compression tests on dry and saturated crushable sand recently reported by the present authors,a new non-linear relationship is proposed between the amount of particle breakage and the plastic work.The expression contains two parameters:(1)a material constant dependent on the grain characteristics and(2)a constant depending on the wetting condition(in this study,dry or saturated).A key finding is that the relationship does not depend on the stress path and,for a given wetting condition,only one set of parameters is necessary to reproduce the results of isotropic,oedometric,and triaxial compression tests.The relationship has been introduced into an elastoplastic constitutive model based on the critical state concept with a double yield surface for plastic sliding and compression.The breakage ratio is introduced into the expression of the elastic stiffness,the critical state line and the hardening compression pressure.Incremental stress-strain computations with the model allow the plastic work to be calculated and,therefore,the evolution of particle crushing can be predicted through the proposed non-linear relationship and reintroduced into the constitutive equations.Accurate predictions of the experimental results in terms of both stress-strain relationships and breakage ratio were obtained. 相似文献
11.
基于冻融次数-物理时间比拟理论的冻土长期强度预测方法 总被引：1，自引：0，他引：1
冻融作用可以改变土的结构,引起其力学特征的变化,从而影响到冻土工程的稳定性。由于冻融周期的设定不尽相同,因此大量的试验结果不能有效地进行对比分析。另外,对于冻融作用下土体力学特征的预测也成为研究的难点。在冻土遗传蠕变理论的基础上,利用球型模板压入仪作为测试方法,提出了一种冻融次数-物理时间比拟的方法。把冻融周期(次数)转化成物理时间(min),将不同冻融周期土的长期强度曲线簇映射到同一坐标中,利用该归一化曲线进行长期抗剪强度的预测,并选取了两种土样进行了测试,分别得到了相关的长期抗剪强度的预测方程。该方法对冻融作用下土体力学行为的成果对比研究以及长期强度的预测有重要的理论意义,对寒区工程稳定性预测分析也具有工程实践价值。 相似文献
12.
冻融循环作用下富平黄土微观结构几何类型变化研究 总被引：1，自引：1，他引：0
冻融循环作用可通过影响寒区土体结构致使基础设施发生破坏,而导致工程失稳宏观现象的根源来自于冻融作用改变了土体的微观结构。为探索冻融作用下土体微观结构变化规律,将富平黄土作为研究对象,分别对其进行0、4、6、8、10、50、100次冻融循环下的电镜扫描观测试验,得到对应次数下的微观照片,对其从颗粒形态、连结方式、排列形式对孔隙的影响三方面进行分析,并且将微观照片中出现的颗粒接触方式以几何模型的方式进行归类,研究几何模型随冻融循环次数增加后的变化规律。结果表明：随着冻融循环次数的增加,土颗粒大小朝着均一性的方向发展,平均粒径呈先减小后增大趋势;颗粒的连结形式从面胶结为主逐渐演变为点接触为主最终再回归为面胶结为主;土体在0~6次冻融循环时孔隙率呈下降趋势,6~8次冻融循环时孔隙率快速上升,之后随着冻融循环次数的增加孔隙率逐渐减小;粒状粒子几何模型变化规律从棱边接触逐渐过渡为粒面接触,扁平状粒子几何模型变化规律从初始粒面接触为主逐渐演变为棱边接触为主,最终再演变为粒面接触。 相似文献
13.
渝东南岩溶山区耕地利用变化下土壤颗粒体积分形特征研究 总被引：2，自引：0，他引：2
通过对重庆东南部喀斯特山区的野外调查采样和室内粒度分析,利用土壤颗粒体积分维模型,分析了该区域耕地土壤与撂荒地土壤颗粒体积分形维数特征,探讨了颗粒体积分形特征与颗粒体积含量的关系。研究结果表明:土壤颗粒体积分形维数与土壤中粘粒(<0.002mm)含量呈明显的线性相关,表现为粘粒含量越高的土壤,其分形维数也越高。土壤粘粒含量与土壤颗粒体积分形维数在不同土地利用方式的土壤剖面上表现出相同的变化规律。土壤分形维数不仅受粘粒含量的支配,还与土壤质地的均一程度有关,分形维数与土壤质地均匀指数表现出一定的相关性,但相关性较弱。耕地土壤分形维数值(平均值为2.5065)大于撂荒地分形维数值(平均值为2.4835),说明岩溶区人类农耕活动对土壤质地尤其是粘粒含量影响明显。土壤体积分形维数可以作为区域耕地土壤质量评价指标之一。 相似文献
14.
An elastoplastic constitutive model for frozen saline coarse sandy soil undergoing particle breakage
The mechanical property of frozen saline sandy soil is complicated due to its complex components and sensitivity to salt content and confining pressure. Thus, a series of triaxial compression tests were carried out on sandy samples with different Na2SO4 contents under different confining pressures to explore the effects of particle breakage, pressure melting, shear dilation and strain softening or hardening. The test results indicate that the stress–strain curves exhibit strain softening/hardening phenomena when the confining pressures are below or above 6 MPa, respectively. A shear dilation phenomenon was observed in the loading process. With increasing confining pressure, the strength firstly increases and then decreases. By taking into consideration the changes between the grain size distributions before and after triaxial compression tests, a failure strength line incorporating the influences of both particle breakage and pressure melting is proposed. In order to describe the deformation characteristics of frozen saline sandy soil, an elastoplastic incremental constitutive model is established based on the test results. The proposed model considers the plastic compressive, plastic shear and breakage mechanisms by adopting the non-associated flow rule. The breakage mechanism can be reflected by an index related to the initial, current and ultimate grain size distributions. The hardening parameters corresponding to compressive and shear mechanisms consider the influence of particle breakage. Then the effect of particle breakage on both the stress–strain and volumetric strain curves is analyzed. The calculated results fit well with the test results, indicating that the developed constitutive model can well describe the mechanical and deformation features of frozen saline sandy soil under various stress levels and stress paths. In addition, the strain softening/hardening, contraction, high dilation and particle breakage can be well captured.
相似文献15.
季节性冻融作用及其对斜坡土体强度的影响——以甘肃黑方台地区为例 总被引：1，自引：0，他引：1
季节性冻土地区黄土斜坡冬春交际常发生崩塌、滑坡等地质灾害,造成了严重的生命财产损失.位于甘肃省永靖县的黄土台塬——黑方台为典型的季节性冻土地区,其3月份黄土滑坡灾害高发.通过对滑坡体的野外调查、原位监测,分析了该地区的冻融作用特征及其对斜坡土体强度的影响,证实了该地区表层土体存在显著的冻融循环作用,总结了斜坡体受冻融作用影响的宏观表现和受气温影响的斜坡表层黄土地温变化过程.在此基础上设计开展了黄土室内力学性质试验,分析了不同初始含水率对冻结黄土三轴抗剪强度参数的影响,对比分析了黄土与冻结黄土的三轴抗剪强度参数变化.由天然和饱和2种状态下的黄土经历15次冻融循环后的直剪实验得出冻融循环作用对黄土强度影响较大的结论.该结果可为冻融期黄土斜坡稳定性分析提供参考. 相似文献
16.
在季节性冻土区,冻融作用诱发黄土滑坡的本质是冻融循环作用下黄土物理力学性质的劣化,探明冻融作用下温度以及水分迁移对黄土强度的影响及其机制是必要的。以山西省柳林县某黄土边坡为例,采用一种新的冻融循环方式即按照土体每年历经的温度路径进行冻融循环,研究在温度动态变化的冻融循环作用下土体的抗剪强度变化规律以及反复冻融循环作用对土体黏聚力、内摩擦角和微观结构的影响。结果表明:在一轮冻融循环过程中,土体强度与温度呈负相关关系,低温对土体强度影响较大。随着冻融次数的增加,土体黏聚力呈指数函数下降,内摩擦角几乎没有明显变化。微观试验表明,随着冻融次数的增加,土体内大颗粒破碎化,孔隙增多,表现为颗粒趋于均一化,中等大小(5~10 μm)孔隙占比最大。本次研究模拟了土体经历的温度变化过程,为该地区季节性冻融型黄土滑坡防治提供了借鉴作用。 相似文献
17.
冻融循环作用是寒区土体力学性质改变的主要影响因素之一。为研究冻融循环作用下寒区冻结掺和土料的动力特性(包括动变形和动强度),以寒区高土石坝砾石掺和土坝料为研究对象,采用低温振动三轴材料试验机,对不同冻融循环次数(0、5、20次)下的冻结掺和土试样进行不同围压和不同动应力幅值比条件下的低温动力循环三轴试验,探讨冻融循环作用对冻结掺和土料的动应力-动应变关系,体变、滞回曲线,轴向累积应变,动回弹模量,残余应变以及动强度的影响。结果表明:随着冻融循环作用的增加,冻结掺和土料的动应力-动应变曲线和体变曲线逐渐稀疏,且试样达到破坏应变的振动次数呈线性减小。通过对不同冻融循环次数下冻结试样的滞回曲线、轴向累积应变、残余变形的研究,发现冻融循环作用使得试样抵抗变形的能力下降。随冻融循环次数的增加,试样的动回弹模量减小,动强度逐渐降低,试样更容易发生破坏。研究结果较好地解释了冻结掺和土料在冻融循环作用下动力变形的机制,可为基于动力变形控制的寒区工程基础设计提供科学参考。 相似文献
18.
针对砂性土颗粒结构的复杂性和不规则性,从颗粒级配和达西定律出发,基于分形几何理论,通过颗粒分析和渗透试验,建立了砂性土颗粒级配分形维数与不均匀系数的关系,从而揭示了级配分形维数的物理意义;通过线性回归,进一步探讨了级配分形维数与渗透系数之间的相关关系。研究发现:级配越好,不均匀系数越大,分维越小,渗透系数也越小。结果表明,级配分形维数是刻画砂性土的颗粒组成及其级配特征的有效参数,直观定量地描述了土的渗透性能,从而为多孔介质以及断层破碎带等裂隙介质的渗透性研究提供了一种较好的研究思路。 相似文献
19.
污泥具有高含水率、力学性质差和污染物含量高等特点,可以通过固化技术将其转化为固化土,达到城市污泥安全处理与合理利用的目的。为了得到在多变的自然气候环境影响下固化土的动力特性,以城市污泥固化土为研究对象,在不同冻融温度和不同冻融循环次数条件下,通过动三轴试验仪对城市污泥固化土进行多振次循环动荷载试验,探讨其在经历不同冻融温度和不同冻融循环次数后的长期动力力学指标变化规律。试验结果表明,污泥固化土破坏形式呈现脆性破坏的特征,并具有明显的剪切面;在低温冻结和多次冻融循环耦合作用下,随着冻融温度降低和冻融循环次数的增加,污泥固化土的轴向应变增速和最终值会随之增大,动强度亦随之降低;对不同时刻动应力-应变曲线进行分析,得到不同冻融温度循环条件下城市污泥固化土动强度与冻融循环次数的关系式,为城市污泥固化土动强度计算提供理论依据。污泥固化土静、动长期强度随冻融次数的变化规律基本一致,在其他条件相同的情况下,污泥固化土静长期强度明显大于其动长期强度。 相似文献