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1.
The ability to model and predict the formation of desiccation cracks is potentially beneficial in many applications such as clay liner design, earth dam construction, and crop science, etc. However, most studies have focused on statistical analysis of crack patterns and qualitative study of contributing factors to crack development rather than prediction. Because it is exceedingly difficult to capture the nonlinear processes during desiccation in analytical modelling, most such models handle crack formation without considering variation of material properties with time, and are unattractive to use in realistic modelling. The data obtained from laboratory experiments on clay soil desiccating in moulds were used as a basis to develop a more refined model of desiccation cracking. In this study, the properties, such as matric suction, stiffness and tensile strength of soil, and base adhesion, could be expressed approximately as functions of moisture content. The initial conditions and the development of suction due to desiccation and the varying material properties were inputted to UDEC, a distinct element code, using its internal programming language FISH. The model was able to capture some essential physical aspects of crack evolution in soil contained in moulds with varying lengths, heights, and materials of construction. Extension of this methodology is potentially beneficial not only for modelling desiccation cracking in clay, but also in other systems with evolving material properties such as concrete structures and road pavements. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
2.
为了探究土体干缩开裂问题,文章采用ERT技术,对黏性土开展了一维干缩开裂动态监测试验。配制初始状态饱和
的泥浆试样,在自然条件下干燥,采用ERT技术获得试样干燥过程中的电阻值变化。结合试样的电阻值图像和裂隙图像,
对土体干缩开裂规律进行了分析。研究结果表明：在干燥蒸发初期,土体电阻值随时间增加缓慢减小,其原因在于土体干
燥收缩导致土颗粒间接触面积增大,颗粒水化膜变薄,进而使得土颗粒表面双电层导电性增强。随着干燥继续进行,气体
进入土体内部,土体由初始饱和状态转变为非饱和状态,电阻值转为缓慢增加。当土体产生裂隙时,裂隙周围土体电阻值
急剧增大,而未发育裂隙的土体电阻依然保持缓慢增加的趋势。通过对比试样电阻值变化曲线和裂隙图像,发现两者所呈
现的裂隙发育位置和状态存在良好的一致性。因此,ERT技术能对干燥过程中土体裂隙发育进行有效的动态监测,准确掌
握裂隙发育的时空动态信息,并且能提前预测裂隙发育的可能位置,为研究极端干旱气候作用下土体的工程性质响应提供
了理想手段。 相似文献
3.
Numerical simulation of desiccation cracking in a thin clay layer using 3D discrete element modeling
Desiccation cracking of clay soil is of critical importance in many applications, such as industrial waste containment, hydraulic barriers, road embankments, and agricultural operations. The factors that influence cracking are known qualitatively, but it is not clear how to predict the initiation and propagation of cracks. This study presents a discrete element approach to modeling desiccation cracking in thin clay layers, considering material property changes. First, an aggregate shrinkage model based on the aggregate structure of clay was proposed, and the drying shrinkage of clay soil was modeled by imposing drying shrinkage kinetics for each aggregate at the micro-scale. Second, the clay soil was represented by an assembly of aggregates linked by bonds, and desiccation cracking of the clay layer was modeled using a three-dimensional discrete element code (PFC3D), with the aid of the embedded programming language FISH. When the clay layer is sufficiently thin, the water content gradient along the section can be neglected; thus, the shrinkage kinetics are the same for all of the grains of clay. In the model based on the discrete element method (DEM), the bond strength and contact stiffness changed during drying. Their changes were determined by matching the simulation results with the experimental data. Third, the DEM approach was validated by reproducing experimental desiccation tests performed on a thin clay layer in a disk shape. The geometric parameters of surface cracks were quantified using image analysis techniques and were compared with experimental observations. Fourth, some factors of influence, such as the sample thickness, the properties of the soil–base interface, micro-mechanical parameters, and shrinkage parameters, were investigated using the DEM model. The results obtained from the DEM analyses were compared with the results of prior research in this field of study. The approach used in this study is very promising for simulating desiccation cracking in thin clay soil because the model captures the initiation and propagation mechanism of desiccation cracks. Although this study was carried out on surface cracking in a thin clay layer, the extension of this methodology is of potential benefit not only for predicting three-dimensional desiccation cracking in real clay liners but also for modeling cracking in other materials with properties that vary with water content or temperature, such as concrete and rock. 相似文献
4.
在干燥环境中,由于蒸发失水,膨胀土发生收缩,表面容易产生纵横交错的裂隙网络(龟裂)。龟裂的产生会极大弱化土体的工程性质,并导致各种工程问题。随着极端干旱气候的频发,膨胀土龟裂问题将会越来越多,越来越显著。开展龟裂研究对揭示龟裂现象的本质规律和指导膨胀土地区的工程实践有重要意义。龟裂的形成和发展是一个动态的过程,与土中水分的蒸发速率、应力状态、收缩特性等直接相关:龟裂形成时水分蒸发处于常速率阶段; 吸力和抗拉强度是制约龟裂形成的两个关键力学参数,当土体中的吸力引起的张拉应力超过土体的抗拉强度时,龟裂便会产生; 龟裂是孔隙发生收缩的直观表现。总体上,力的作用和收缩空间是土体龟裂形成的两个必要条件。此外,膨胀土龟裂具有非常复杂的发生发展过程,受土质学、土力学、土结构、试验条件和方法等许多因素的影响。龟裂定量分析是龟裂研究的重要内容之一,能为龟裂机理研究及相关理论模型的建立提供必要参数。计算机图形处理技术具有效率高、操作性强、精度高等优点,为龟裂定量分析提供了强有力的工具。目前关于土体龟裂研究还存在许多不足之处,在今后的工作中,应该重视龟裂形成和发展过程的动态特征,围绕与土体龟裂相关的水-土作用关系、力学机制、收缩变形机制、大尺度现场试验和三维观测分析技术等方面开展更多的针对性研究,综合考虑龟裂形成过程中的土质学、土力学和土结构因素,结合宏观现象与微观分析,建立土体龟裂的理论体系。 相似文献
5.
新近系三趾马红土黏粒含量高,失水干燥易开裂形成干缩裂纹。为研究干密度对三趾马红土干燥开裂行为影响,利用自制干燥装置开展压实三趾马红土脱湿试验,并采用数字图像相关(DIC)方法分析其表面干缩裂纹扩展与自愈规律。结果表明:(1)不同初始干密度试样干燥过程中均出现开裂现象,其表面干缩裂纹演化过程可分裂纹萌生、裂纹扩展、裂纹自愈、裂纹稳定4个阶段;小干密度试样表面干缩裂纹网络展布密集均匀,而大干密度试样表面开裂以“宽大稀疏”裂纹为主;(2)试样表面应变场变化能够较好反映试样表面干缩裂纹演化过程,蓝色压应变区代表试样失水整体产生的体积收缩,红色应变条带代表试样表面受拉而产生的干缩裂隙;试样干燥过程表面蓝色压应变区不断扩大,红色拉应变条带区逐渐变小,表明表面裂纹受到试样整体收缩牵拉而产生“自愈”收缩。且干密度越小,试样干缩过程表面红色拉应变网络越密集,干缩裂纹自愈程度越高;(3)试样表面应变场变化表明各等级干缩裂纹均出现自愈现象,但主裂纹的主应变减少量最大,自愈程度最高,对试样整体裂纹自愈起主导作用;试样初始干密度越小,各等级裂纹的峰值应变越大,自愈时的应变缩减量越高,表明试样失水收缩特征越显著。研究成果对进一步揭示压实黏土干燥裂纹的复杂演化过程机理研究提供新参考。 相似文献
6.
This paper presents a numerical study on the desiccation cracking process of clayey soil. The initiation and propagation of cracks were investigated using finite element code, including the damage-elastic cohesive fracture law to describe the behaviour of cracks. The coupling between the hydraulic behaviour (moisture transfer in the soil matrix and in the cracks) and the mechanical behaviour (volume change of the soil matrix and development of cracks) were also considered. The results of a laboratory experiment performed on clay soil, taken from a literature review, were used to evaluate the numerical modelling. The results show that the code can reproduce the main trends observed in the experiment (e.g., shrinkage related to drying, crack development). In addition, the numerical simulation enables the identification of other phenomena, such as the evolution of suction and stress related to drying and the development of a single crack. These phenomena are difficult to observe experimentally. 相似文献
7.
Moisture Movement Through Cracked Clay Soil Profiles 总被引：1，自引：0，他引：1
Delwyn G. Fredlund Sandra L. Houston Quan Nguyen Murray D. Fredlund 《Geotechnical and Geological Engineering》2010,28(6):865-888
A continuum mechanics approach is used for the formulation of unsaturated hydraulic conductivity functions and the water storage
functions for fractured or cracked clay soils in this parametric study. Suggested procedures are based on available research
literature related to the behavior of cracked unsaturated porous media. The soil–water characteristic curve, hydraulic conductivity
and water storage functions take on the character of bi-modal unsaturated soil property functions. The bimodal character arises
out of the independent behavior of the cracks and the intact clay soil. Matric suction changes beneath a slab-on-grade foundation
placed on a cracked clay soil profile are modeled for varied surface flux conditions using the proposed unsaturated hydraulic
conductivity and water storage functions. The impact of various levels of surface cracking on soil suction distributions is
discussed. Suction distribution patterns are dependent on the initial soil surface suction. In particular, the results are
dependent upon whether the initial matric suction is less than or greater than the air entry of the cracked clay. There is
an extremely wide range of possible conditions that could be modeled but the parametric study results presented in this paper
are limited to a series of selected crack widths and densities for an exfiltration case and an infiltration case. 相似文献
8.
干湿循环条件下重塑膨胀土的裂隙发育特征及量化研究 总被引：2，自引：0，他引：2
裂隙性是膨胀土的典型工程地质特性之一,对其工程性质有重要影响,直接或间接地导致各种工程问题。通过对重塑膨胀土开展室内干湿循环试验,对获得的裂隙数字图像采用图像处理技术进行一系列预处理操作,提出了表面裂隙率、裂隙条数、裂隙总长度、裂隙平均宽度和绝对收缩率等量化指标,定量描述裂隙的形态特征,分析干湿循环过程中压实膨胀土的裂隙发育规律。结果表明:含水率和干湿循环次数是影响膨胀土裂隙发育的重要因素。随着含水率的减小,重塑膨胀土的裂隙发育程度总体上有增加的趋势。表面裂隙率、裂隙条数和总长度随含水率的减小逐渐增加,绝对收缩率随含水率减小而增大,而裂隙宽度与含水率之间没有明显的规律;随干湿循环次数的增加,裂隙进一步发育,裂隙条数、裂隙总长度、表面裂隙率增加,绝对收缩率总体增大,但裂隙平均宽度存在减小的现象,这与后期发育的大量微裂隙有关。 相似文献
9.
Cracks are common in clayey or expansive soils and provide preferential pathways for water infiltration into soils. A field study was conducted to investigate the mechanisms of initiation and development of desiccation cracks on two soils. Based on results of the field study and measurements of soil-water retention curves and soil shrinkage properties in the laboratory, the conditions of crack initiation and the development of crack geometric parameters (i.e., crack porosity, crack aperture, and crack density) with water content or drying time were quantified. The results show that desiccation cracks developed in three stages: initial stage, primary stage, and steady state stage. In the initial stage, few cracks developed with gradually decreasing water content. When the water content reached a critical value for crack initiation, cracks developed quickly and this was the start of the primary stage. The critical suction at crack initiation was calculated using a stress criterion, which is in the range of 5.3–21.3 times the preconsolidation pressure of the soil. As the water content approached the shrinkage limit of the soil, cracks developed slowly and approached a steady state. The cracks were found to be repeatable during three drying–wetting cycles. 相似文献
10.
Marcelo Sanchez Alvis Atique Sewon Kim Enrique Romero Marcin Zielinski 《Acta Geotechnica》2013,8(6):583-596
The study of desiccation cracks in soils has been a subject of increasing attention in recent research. This paper presents the use of a 2D profile laser that is coupled with a motion controller (that allows scanning the overall surface of a drying soil) and electronic balance (to measure the water loss). The aim is to accurately track the three most relevant variables associated with the behavior of soils during desiccation: volume change, water loss and evolving crack network’s morphology. The paper presents the methodology to obtain a digital model of the soil using the experimental setup described above. The main results of a natural soil subjected to drying are presented and discussed, including evolution of cracks aperture; evolution of cracks depth, surface contour levels (at different times); and evolution of volume change. It is shown that the proposed methodology provides very useful information for studying the behavior of soils subjected to desiccation. 相似文献
11.
Numerical modelling of a field soil desiccation test using a cohesive fracture model with Voronoi tessellations 总被引：1，自引：0，他引：1
Numerical modelling of a field soil desiccation test is performed using a hybrid continuum-discrete element method with a mix-mode cohesive fracture model and Voronoi tessellation grain assemblages. The fracture model considers material strength and contact stiffness degradation in both normal and tangential directions of an interface. It is found that the model can reasonably reproduce the special features of the field soil desiccation, such as curling and sub-horizontal crack. In addition, three significant factors controlling field desiccation cracking, fracture energy, grain heterogeneity and grain size are identified. 相似文献
12.
章君政唐朝生巩学鹏周启友程青吕超施斌 《岩土力学》2023,(2):392-402
土体在气候作用下发育干缩裂隙是一种常见的自然现象,裂隙的存在会极大弱化土体的工程性质,诱发许多岩土与地质工程问题。为了实时掌握黏性土中干缩裂隙网络的发展状态,提出了一套基于高密度电阻率层析成像技术（ERT）的土体干缩裂隙动态发展过程精细监测方法。分别开展模型试验及原位试验,利用自行研制的测定系统持续采集电流-电位差数据,随后利用自行开发的有限元法电阻率层析成像（FemERT）系统进行数据处理,获取了裂隙网络在不同发育阶段的空间分布特征。结果表明：（1）ERT可以实现土体裂隙发育过程的精细监测,具备监测三维裂隙网络几何形态的能力,裂隙宽度的识别精度达到毫米级,裂隙深度的识别精度达到厘米级;（2）ERT的感度分布特征解释了裂隙发育对于土体电阻率的影响规律,测定电阻值时程曲线因裂隙产生位置的不同而呈现不同的变化规律;（3）反演电阻率及其相对变化率（Rev）可以直观表征裂隙网络在不同阶段的空间几何形态,凸显裂隙动态发育过程对于土体导电性的影响。 相似文献
13.
膨胀土工程地质特性研究进展 总被引：1，自引：0，他引：1
根据近年来国内外学者围绕膨胀土工程地质特性取得的研究成果,着重从胀缩性、裂隙性、超固结性、强度、渗透性、微观结构及工程处治技术等几个方面总结了该课题的研究现状及进展,得到如下认识:（1）胀缩性主要取决于强亲水性黏土矿物含量、水/力边界条件及初始状态,在干湿循环条件下具有不可逆性,关于胀缩机理学界存在不同的观点;（2）裂隙性是膨胀土区别于一般土体的显著特征之一,裂隙的存在会极大破坏土体的整体性,弱化力学性质,是许多工程地质问题的直接或间接原因,裂隙形成过程与膨胀土矿物成分、微观结构和干燥过程中的内应力发育状态有关;（3）超固结性使膨胀土具有较大结构强度和水平应力,易在开挖过程中引起较强的卸荷效应,是促进边坡失稳的重要因素;（4）膨胀土的强度随干湿循环次数增加而逐渐降低,并最终趋于稳定,其中裂隙发育和土结构调整在此过程中起关键作用;（5）渗透性在很大程度上受裂隙的控制,但目前关于两者之间的定量关系还缺少系统研究;（6）微观结构反应了膨胀土的形成条件和应力历史,是决定其宏观物理力学性质的主要因素,开展微观结构研究是掌握膨胀土宏观性质本质规律的重要途径。在工程处治技术上,本文重点介绍了近些年发展起来的膨胀土路堤物理处治技术和路堑边坡柔性支护技术。最后,针对该课题的研究现状,笔者提出了今后的研究重点和方向,主要包括胀缩性和力学性质的各向异性、裂隙形成的力学机理、裂隙形态特征与工程地质特性之间的定量关系、宏-微观力学模型耦合问题及多场耦合作用下膨胀土工程性质响应特征等。 相似文献
14.
针对土遗址干缩裂缝病害,以三星堆月亮湾城墙剖面为依托,探讨干缩裂缝的开裂条件、扩展特征以及失稳扩展条件。研究结果有助于揭示土遗址开裂规律,对遗址保护的工程实践具有指导意义。针对月亮湾城墙土体进行室内干燥试验,通过电子天平记录试样失水过程,采用图像分析技术得到裂缝的开裂与扩展过程,利用数字图像相关技术得到开裂过程的位移场与应变场。结果表明:试样表面缺陷降低了开裂所需的拉应力,缺陷与边界的距离越小,引发开裂的缺陷临界尺寸就越小,因此裂缝更易在试样边界附近缺陷处产生;根据断裂力学理论,考虑含水率对土体性质的影响,裂缝失稳扩展需满足应力强度因子对含水率的增加率大于断裂韧性;理论推导出裂缝失稳扩展临界长度的计算方法,该方法初步得到了实测数据验证;随着含水率从45.6%降低到29.1%,失稳扩展临界长度与试样宽度比值从0.109减小到0.024,含水率越低裂缝越易进入失稳扩展阶段,开裂处一个微小的缺陷就可能引发裂缝的快速扩展;对土遗址表面进行保护时,应着重修补分布在土层边界区域的大尺寸缺陷;定期监测土遗址临空面,一旦发现开裂,应及时对裂缝及其附近缺陷进行修复,以防止裂缝失稳扩展。 相似文献
15.
Soils, as well as most of deformable multiphase porous materials, are likely to suffer from desiccation cracking, leading to the formation of regular crack patterns affecting their permeability. The ensuing crack spacing has often been related to a concept sometimes called “sequential infilling”: it is assumed that desiccation cracks are formed by successive generations. However, such a concept does not consider the pattern of a simultaneous crack formation at a given moment. Using our desiccation cracking test results and their numerical simulation, we propose a consistent explanation for the formation of desiccation crack patterns in soils. We show that the “sequential infilling” concept is suitable only when the position of the crack(s) clearly stems from the stress field. To derive an estimate of the desiccation crack spacing, the overall energy of the system needs to be considered. Statistical variability should be superimposed on the mean deterministic conditions discussed here. 相似文献
16.
Geometric parameters and REV of a crack network in soil 总被引：3，自引：0，他引：3
Cracks are common in natural and engineered soils and provide preferential pathways for water infiltration into the soil. Statistical properties of crack geometries are important inputs for analyzing preferential flows in discrete random crack networks. This paper reports the outcome of a field study conducted on a compacted, cracked soil ground at a steady moisture condition. The objectives of the field study were to investigate the crack patterns and probability distributions of the geometric parameters of cracks and to determine the representative elementary volume (REV) of the crack network. The desiccation cracks at the survey site formed an inter-connected columnar structure. The traces of the cracks on the soil surface formed a primary structure consisting of inter-connected crack polygons and a secondary structure comprising of isolated cracks. The locations and orientations of the desiccation cracks followed a uniform distribution, differing from the distribution of fracture sets often observed in fractured rocks. The lengths and apertures of the cracks followed a lognormal distribution as expected. The REV size for the cracked soil was found to be approximately five times the mean crack length, above which the variation in crack porosity in relation to domain size was negligible. 相似文献
17.
Soil desiccation cracking is important for a range of engineering applications, but the theoretical advancement of this process is less than satisfactory. In particular, it is not well understood how the crack spacing-to-depth ratio depends on soil material behaviour. In the past, two approaches, namely stress relief and energy balance, have been used to predict the crack spacing-to-depth ratio. The current paper utilises these two approaches to predict the approximate spacing-to-depth ratio of parallel cracks that form in long desiccating soil layers subjected to uniform tensile stress (or suction profile) while resting on a hard base. The theoretical developments have examined the formation of simultaneous and sequential crack patterns and have identified an important relationship between the stress relief and energy approaches. In agreement with experimental observations, it was shown that the spacing-to-depth ratio decreases with layer depth, and crack spacing generally increases with layer depth. The influence of the stiffness at the base interface indicated that decreasing the basal interface stiffness makes the crack spacing to increase in sequential crack formation. The experimental observations also show a decrease in cracking water content with the decrease in layer thickness, and this behaviour was explained on the basis of a critical depth concept. 相似文献
18.
膨胀土具有多裂缝性的不良工程特性,对边坡等膨胀土地区工程具有潜在威胁。再生橡胶加筋膨胀土(ESR)对膨胀土动力、静力以及胀缩性有良好的改良效果。膨胀土的裂缝演化形态会受到土样厚度的影响,本文使用橡胶加筋膨胀土,对照素膨胀土探究橡胶粉末对膨胀土裂缝演化的影响与ESR裂缝的厚度效应。试验共设计未添加橡胶素膨胀土与ESR各4组不同厚度试样展开研究,结果如下:(1)膨胀土自然干燥过程含水率可分为3阶段变化,ESR的含水率变化更为迅速;(2)膨胀土的开裂过程存在明显厚度效应,ESR的厚度效应相较更不明显,裂缝演化更具有均匀性;(3)膨胀土开裂过程中的裂缝总长度与总面积受厚度效应影响严重,橡胶加筋可以约束膨胀土裂缝长度与面积并减少不同厚度样品间差值;(4)膨胀土裂缝发育的分形维数最终在1.4~1.5之间,不同厚度橡胶加筋膨胀土的分形维数变化更为接近。 相似文献
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Influencing factors of geometrical structure of surface shrinkage cracks in clayey soils 总被引：7，自引：0，他引：7
In order to investigate the effects of temperature, thickness of soil layer, wetting and drying cycles and soil types on geometrical structure of surface shrinkage cracks in clayey soils, special software Crack Image Analysis System (CIAS) for analyzing shrinkage crack patterns was developed. Eight groups of soil samples were prepared and subjected to drying to crack in laboratory. The number of crack segments and intersections, average crack length, width and aggregate area, crack intensity factor (CIF), and the corresponding probability density functions (PDF) of these parameters were determined by analyzing several crack patterns derived from different experimental conditions. The results show that the soil cracking behavior and the geometrical structure of crack patterns are significantly influenced by these considered factors. There is a tendency of crack length, width, aggregate area and their most probable value (MPV) related to the PDF increases with temperature increase. With thicker soil layers, the average crack length, width, aggregate area and CIF are increased, and the main distribution ranges of crack length, width and aggregate area are increased also. When the soil is subjected to multiple wetting–drying cycles, the soil surface generates more irregular and coarse cracks. The number of short and narrow crack segments increases significantly, and the CIF decreases with an increase in wetting–drying cycles. It is also observed that the extent of cracking is directly related to the soil fines fraction and its plasticity index (IP). The greatest CIF and crack width are observed in the soils with the largest fines fraction and highest IP. In addition, the ratio of numbers of crack segments to intersections ranges from 1.5 to 2, and cracking mainly takes place in three stages: main-cracks initiation stage; sub-cracks initiation stage; terminal stable stage. 相似文献