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1.
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
2.
This paper presents some experimental results on desiccation cracking tests conducted on thin layers of clay soils. Observation
of the evolution of cracking patterns was examined to clarify the transient mechanisms of the crack formation of clay soils.
Laboratory experimentation on desiccation cracking was carried out to examine experimentally the quantitative relationships
between the characteristics of soil cracks and the prevailing controlling conditions. Five desiccation cracking tests for
slurried clay soils were carried out using shrinkage moulds in a humidity chamber, which was capable of controlling relative
humidity and temperature. The soil used in the experimental studies was residual basaltic clay and was classified as a highly
reactive soil. In order to provide simple conditions for theoretical modelling, the tests were conducted in perspex and metal
moulds with rectangular cross-sections. The lengths of the moulds were considerably larger than their widths so that parallel
cracking were generated in thin layers. In each cracking test, several rectangular moulds of different thicknesses and widths
were used. Some of these tests were used for observation, crack initiation and evolution, and others for moisture content
measurement during desiccation. The test results include evolution of the cracking pattern, influences of speed of desiccation
and typical crack spacing to depth ratios for soil layers. 相似文献
3.
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
4.
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
5.
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
6.
红层泥质胶结物在干燥条件下会因含水率变化产生开裂,裂缝进一步发展贯通最终导致红层泥岩崩解破坏。目前对红层泥岩崩解机制的研究多为定性描述,缺乏定量分析方法。因此,定量研究红层泥质胶结物开裂的产生及扩展对深化红层泥岩崩解理论研究具有重要意义。基于线弹性断裂力学及非饱和土力学,建立了考虑含水率变化的红层泥质胶结物裂缝深度及间距计算公式,并对公式参数敏感性进行了分析。应用CT试验数据对PFC2D数值模型进行了校准,并基于干缩开裂数值试验结果,对裂缝深度及间距计算公式进行了对比验证。结果表明：提出的计算公式能较好地预测红层泥质胶结物的开裂深度及间距,裂缝深度随含水率减小呈先快速增加再缓慢增长的特点。研究成果有助于加深对红层泥岩崩解的量化理论分析,并为预测工程中红层泥岩的开裂程度提供参考。 相似文献
7.
8.
Xu-Dong Zhang Yong-Gui Chen Wei-Min Ye Yu-Jun Cui Yong-Feng Deng Bin Chen 《Environmental Earth Sciences》2017,76(15):531
Bentonite has been proposed for use as an engineering barrier and buffer in nuclear waste repositories and has been used frequently in municipal waste landfills. The cracking behavior and deformation properties of this material can be influenced by the chemistry of pore water. In the present work, the influence of salt concentration on the desiccation cracking behavior of GMZ bentonite was investigated with laboratory experiments. Image processing techniques and SEM tests were performed on the specimens which had undergone the desiccation testing in order to analyze the cracking mechanisms. Results show that the water evaporation process can be identified by a steady rate stage, a falling rate stage and a residual stage. The water evaporation rate is strongly affected by the salt concentration of the pore water; higher salt concentrations result in lower evaporation rates; the final water content is strongly impacted by a high initial salinity; otherwise the water contents are very similar for the residual stage. During desiccating, most of cracks appeared at the steady evaporation stage. The cracking morphology and patterns were greatly affected by the salt concentration of the pore water; and larger crack lengths and lower crack densities were obtained as the initial salinity was increased. 相似文献
9.
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
10.
颤痕是冰川作用地区由冰川携带岩屑做周期性或间歇性运动在冰床基岩和冰碛石表面形成的新月形或弧形破裂形态,特征尺度一般不大于1 m。其主要形成机制类似Riedel构造模式中的（R）剪切破裂和（T）拉张破裂,且遵循脆性破裂原理。根据国内外文献报道和野外考察,从术语学角度将冰川颤痕分为狭义和广义两种。广义冰川颤痕,包括曲锥形擦口（狭义颤痕）、半月形裂口、新月形凿口、新月形裂纹和新月形断口5种。测量统计结果显示,23组新月形断口的排列间距,KS和JB检验均符合正态和伽玛分布（置信度95%）,与岩石节理（破裂）的间距特征一致;25组新月形凿口和35组新月形裂纹的排列间距,KS检验符合正态分布和伽玛分布,JB检验不符合正态分布（置信度95%）。证明颤痕在空间分布上大体保持相等的破裂间距,基本符合饱和模式理论。颤痕的定向性、成组特征具有明确的环境意义,与擦痕、擦面的地貌组合是重要的冰川遗迹判别标志。缺少冰蚀地貌组合的孤立“颤痕”,不具有指示冰川作用的价值。近年报道的山东鲁山没有“颤痕”等冰川遗迹。 相似文献
11.
The paper presents a simple approximate analytical solution of the remote stresses that cause the collapse of a borehole or other circular cylindrical cavity in an infinite elastic space. Regions of parallel equidistant splitting cracks are assumed to form on the sides of the cavity. Their boundary is assumed to be an ellipse of a growing horizontal axis, the other axis remaining equal to the borehole diameter. The slabs of rock between the splitting cracks are assumed to buckle as slender columns, and their post-critical stress is considered as the residual stress in the cracked rock. The buckling of these slab columns is assumed to be resisted not only by their elastic bending stiffness but also shear stresses produced on rough crack faces by relative shear displacements. The energy release from the infinite medium caused by the growth of the elliptical cracking region is evaluated according to Eschelby's theorem. This release is set equal to the energy dissipated by the formation of all the splitting cracks, which is calculated under the assumption of constant fracture energy. This yields the collapse stress as a function of the elastic moduli, fracture energy, ratio of the remote principal stresses, crack shear resistance characteristic and borehole diameter. The collapse stress as a function of crack spacing is found to have a minimum, and the correct crack spacing is determined from this minimum. For small enough diameters, the crack spacing increases as the (4/5)-power of the borehole diameter, while for large enough diameters a constant spacing is approached. In contrast to plastic solutions, the breakout stress exhibits a size effect, such that for small enough diameters the breakout stress decreases as the (? 2/5)-power of the borehole diameter, while for large enough diameters a constant limiting value is approached. Finally, some numerical estimates are given and the validity of various simplifying assumptions made is discussed. 相似文献
12.
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
13.
An energy approach is proposed as a complement to the stress approach commonly considered for investigating soil desiccation cracking. The elastic strain energies before and after crack initiation are estimated by both numerical and analytical solutions. The energy released by cracking is then compared with the fracture energy to discuss crack initiation conditions. This leads to combined energy and stress conditions for crack initiation following Leguillon's theory. An approximate analytical solution is derived from a variational formulation of the porous elastic body equations. A cohesive zone model and finite element code are used to simulate crack propagation in an unsaturated porous body. This analysis shows that the energy criterion is reached before the stress criterion, and this can explain unstable crack propagation at the beginning. The approximate analytical solution allows predicting correctly the crack depth and opening in its initiation stage. 相似文献
14.
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
15.
Cracking and coalescence behavior in a rectangular rock-like specimen containing two parallel (stepped and coplanar) pre-existing open flaws under uniaxial compression load has been numerically studied by a parallel bonded-particle model, which is a type of bonded-particle model. Crack initiation and propagation from two flaws replicate most of the phenomena observed in prior physical experiments, such as the type (tensile/shear) and the initiation stress of the first crack, as well as the coalescence pattern. Eight crack coalescence categories representing different crack types and trajectories are identified. New coalescence categories namely “New 1” and “New 2”, which are first observed in the present simulation, are incorporated into categories 3 and 4, and category 5 previously proposed by the MIT Rock Mechanics Research Group, respectively. The flaw inclination angle (β), the ligament length (L) (spacing between two flaws) and the bridging angle (α) (inclination of a line linking up the inner flaw tips, between two flaws) have different effects on the coalescence patterns, coalescence stresses (before, at or post the peak stress) as well as peak strength of specimens. Some insights on the coalescence processes, such as the initiation of cracks in the intact part of specimens at a distance away from the flaw tips, and coalescence due to the development and linkage of a number of steeply inclined to vertical macro-tensile cracks are revealed by the present numerical study. 相似文献
16.
17.
水力压裂技术广泛使用于页岩气开采工程中。为了分析压裂过程中多裂缝扩展形成复杂裂缝网的机制,尝试将态型近场动力学理论引入页岩水平井水力压裂过程的力学建模与数值仿真,在物质点间相互作用力模型中加入等效水压力项以实现在新生裂缝面上跟踪施加水压力,建立了水力压裂过程的近场动力学分析模型。通过模拟页岩储层的水力压裂过程,可得到复杂的裂缝扩展路径、裂缝网络的形成过程以及裂缝扩展受射孔间距及页岩天然裂缝和层理的影响。研究结果表明:射孔间距过小会造成起裂干扰,使中心射孔的裂缝扩展受到抑制;在压裂压力一定的情况下适当增大射孔间距,可以显著增强页岩压裂形成裂缝网的能力;压裂过程中水平层理面可能张开形成水平裂缝,且天然裂缝会诱导形成更复杂的垂直裂缝。模型和方法可为页岩水力压裂过程和机制研究及工程实践提供参考。 相似文献
18.
Peng-Zhi Pan Jonny Rutqvist Xia-Ting Feng Fei Yan Quan Jiang 《Rock Mechanics and Rock Engineering》2014,47(6):2183-2198
We present a formulation of a discontinuous cellular automaton method for modeling of rock fluid pressure induced fracture propagation and coalescence without the need for remeshing. Using this method, modelers discretize a discontinuous rock-mass domain into a system composed of cell elements in which the numerical grid and crack geometry are independent of each other. The level set method, which defines the relationship between cracks and the numerical grid, is used for tracking the crack location and its propagation path. As a result, no explicit meshing for crack surfaces and no remeshing for crack growth are needed. Discontinuous displacement functions, i.e., the Heaviside functions for crack surfaces and asymptotic crack-tip displacement fields, are introduced to represent complex discontinuities. When two cracks intersect, the tip enrichment of the approaching crack is annihilated and is replaced by a Heaviside enrichment. We use the “partition of unity” concept to improve the integral precision for elements, including crack surfaces and crack tips. From this, we develop a cellular automaton updating rule to calculate the stress field induced by fluid pressure. Then, the stress is substituted into a mixed-mode fracture criterion. The cracking direction is determined from the stress analysis around the crack tips, where fracture fluid is assumed to penetrate into the newly developed crack, leading to a continuous crack propagation. Finally, we performed verification against independent numerical models and analytic solutions and conducted a number of simulations with different crack geometries and crack arrangements to show the robustness and applicability of this method. 相似文献
19.
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