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1.
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
2.
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
3.
In the present study, influence of wetting–drying cycles on swelling pressures of sand–bentonite mixtures used in the construction
of sanitary landfills to have an impermeable liner was investigated before and after lime treatment of the mixtures. Swelling
pressure tests were conducted to see if the swelling pressures were affected by wetting–drying cycles. First series of specimens
were prepared as a mixture of sand and bentonite only. In the first series of specimens, sand was mixed with bentonite in
various proportions with their optimum water contents and compacted by using standard proctor energy. In the second series
of the specimens, lime in various proportions was added to the mixtures of sand–bentonite. Then, the sand–bentonite mixtures
stabilized by lime were compacted with the standard proctor energy at their optimum moisture contents. Five wetting–drying
cycles were performed on each specimen and values of swelling pressures were measured at the end of each cycle. Results of
swelling pressure tests indicated that the swelling pressure is decreased when lime is added to the mixtures. In addition,
decrements were observed on swelling pressures by wetting–drying cycles. The results of the experiments of this investigation
showed that the beneficial effect of lime stabilization to control the swelling pressures was partly lost by the wetting–drying
cycles. However, the test results indicated that the swelling pressures of the specimens made of sand–bentonite mixtures stabilized
by lime were lower than the swelling pressures of the specimens made of only sand–bentonite mixtures. 相似文献
4.
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
5.
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
6.
通过室内试验研究了土壤干缩裂缝发育规律,采用数字图像处理技术与AutoCAD测量功能,分析了不同含水率下土壤裂缝网络几何形态特征.结果表明:土壤含水率达到43%时出现裂缝,裂缝骨架长度、周长和面积分别在含水率达到23%、23%、7%时趋于稳定,裂缝平均宽度的发育经历了波动增长、线性增长和稳定3个阶段,并在含水率达到7%时保持不变;裂缝条数与节点数之比随含水率降低而减小,并最终保持在1.67,此结果与收缩块区分散度和裂缝交叉角度分布规律共同表明,裂缝网络形态呈方形正交网络分布趋势,且处于方型网络与“T”型正交网络之间;裂缝平均弯曲度随含水率减小,由1.06减小至1.02并保持恒定,揭示了裂缝整体弯曲程度与不同时期裂缝弯曲的变化规律. 相似文献
7.
在工程建设与自然环境中,土体因失水而产生收缩、开裂的过程受多重因素的影响,且各因素之间的相互作用关系十分复杂。其中,环境温度在土体开裂的起始与结束中,起至关重要的影响;同时,鲜见关于土体内部黏土、砂粒配比对于裂隙发育影响的研究。故本研究设置了不同环境温度、含砂率条件,展开一系列室内蒸发试验,通过记录试验过程中土体内部水分散失以及表面裂隙发育、发展情况,利用相关图形分析软件,对裂隙率、裂隙网络的几何形态进行定量分析,进而探究不同温度、含砂率对土体干缩、开裂的影响机理。研究结果表明：（1）砂粒的存在,导致土体内部的结构发生改变,部分输水通道被堵塞,从而延长了自由水的运移路径,水分蒸发速率随着含砂率的增加而降低。（2）砂粒的存在将导致土体表面提前产生开裂,此现象受含砂率的影响较小,与是否含砂有关。（3）土体内部含砂率越高,裂隙发育纵深越小,延伸长度越短,同时裂隙的宽度与含砂率呈反比。（4）相同含砂率条件下,环境温度越高,水分蒸发速率、土体表面形成的裂隙宽度越大,且在一定程度上促使表面裂隙提前产生。 相似文献
8.
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
9.
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
10.
干湿循环对非饱和膨胀土抗剪强度影响的试验研究 总被引：1，自引：0，他引：1
膨胀土是一种气候敏感性土体,研究在干湿循环过程中膨胀土剪切强度的变化,对了解在自然界周期性蒸发和降雨作用下原位膨胀土体工程性质的变化以及由此导致的地质灾害发生过程具有重要意义。文中以重塑非饱和膨胀土为研究对象,模拟了3次干湿循环过程,对每次干燥路径中的试样进行了直剪试验,重点分析含水率、正压力及干湿循环次数对膨胀土剪切强度的影响,得到如下主要结果：（1）在干燥过程中,随着含水率的减小,试样的刚度、脆性、抗剪强度值（峰值剪切应力）、抗剪强度指标（黏聚力、内摩擦角）及抗剪强度损失（峰值强度与残余强度之差）均呈增加趋势;（2）正压力越高,试样的剪切强度和残余强度越大,而破坏后的峰值强度损失越小,破坏韧性增加;（3）在3次干燥过程中,试样的剪切强度及黏聚力呈先增加后减小的趋势,在第二次干燥过程中达到峰值,但内摩擦角受干湿循环的影响无明显规律;（4）试样经历多次干湿循环后,其剪切特性越来越类似于超固结土,脆性显著增加;（5）干燥过程和干湿循环对试样残余剪切强度的影响都不明显,残余剪切强度基本都在100 kPa附近变化;（6）非饱和膨胀土在干湿循环及干燥过程中剪切强度的变化除了与吸力有关外,还与其微观结构调整和裂隙发育状态密切相关,需要综合非饱和土力学和土质学理论对试验现象进行分析。 相似文献
11.
This paper is aimed at showing the efficiency of discrete element modelling for the prediction and understanding of drying shrinkage and associated cracking. The discrete element approach used is presented first. Cohesive forces between grains, as well as drying shrinkage deformation, are included in the formulation. A numerical model is then used to simulate drying shrinkage experiments conducted on a fine-grained soil. The numerical simulations agree well with the experimental measurements. When drying shrinkage is constrained at the boundaries, and when moisture gradients develop in the drying soil, the model is able to predict the time of the occurrence of cracking, as well as the crack pattern formed. Finite element simulations and the discrete element approach both predict similar behaviours before cracking occurs. The proposed discrete element approach is highly promising for studying the origins and causes of cracking in soils. 相似文献
12.
13.
开展了湿干循环作用下压实黏土的开裂试验和微观结构特性研究,分析了湿干循环作用对黏土开裂和孔隙结构的影响,将压汞试验(MIP)和扫描电镜(SEM)的结果与宏观开裂进行比较。结果表明:湿干循环作用显著影响了压实黏土的开裂,用开裂因子表征黏土的开裂程度,开裂因子随含水率减小而增大并明显大于湿干循环作用前; 随湿干循环次数的增加,黏土孔隙的总体积、中间孔径、平均孔径、平均孔隙率和团粒内孔隙均在增加,而黏土的颗粒内孔隙、颗粒间孔隙和团粒间孔隙却在减小。湿干循环作用使黏土体从大团粒逐渐转化为小颗粒,并增大了土颗粒的凸凹性,分析SEM二值化图像得知土体孔隙率均在增加; 用压汞法和扫描电镜法分析和解释土体开裂是可行的,所得的微观孔隙特征与宏观开裂规律基本相符。 相似文献
14.
利用偏光显微镜对经历不同高温循环作用后的细粒大理岩进行观测,通过统计微裂纹长度、开度、数量等参数,探讨不同加热循环次数后岩样内微裂纹的扩展规律。结果表明,（1）经历不同热循环次数作用的岩样,微裂纹的数量和长度均不同,未经热处理岩样内颗粒致密,胶结较好,内部无明显的微裂纹。经历4次热循环作用后岩样内微裂纹发育明显,以晶界裂纹为主,开度和长度均显著增加。岩样经历16次热循环作用后开度持续增大,为55 µm,是4次热循环的4倍;（2）对不同热循环处理后岩样内部发育微裂纹的方向进行了统计,发现微裂纹无明显的方向性,还表明细观切片的取样位置对微裂纹的发育影响不大;（3）线性裂纹密度随热循环次数的增加而增大,经历16次热循环作用后岩样的线性裂纹密度是没有经历热处理岩样的21倍。 相似文献
15.
Trong Vinh Duong Yu-Jun Cui Anh Minh Tang Jean-Claude Dupla Jean Canou Nicolas Calon Alain Robinet 《Acta Geotechnica》2016,11(1):51-59
This paper deals with the resilient behavior of the interlayer soil which is created mainly by the interpenetration of ballast and subgrade soils. The interlayer soil studied was taken from a site in the southeast of France. Large-scale cyclic triaxial tests were carried out at three water contents (w = 4, 6 and 12 %) and three fines contents corresponding to 5, 10 % subgrade added to the natural interlayer soil and 10 % fine particles (<80 μm) removed from the natural interlayer soil. Soil specimens underwent various deviator stresses, and for each deviator stress, a large number of cycles was applied. The effects of deviator stress, number of cycles, water content and fines content on the resilient modulus (M r) were analyzed. It appears that the effects of water content and fines content must be analyzed together because the two effects are closely linked. Under unsaturated conditions, the soil containing high fines content has higher resilient modulus due to the contribution of suction. When the soil approaches the saturated state, it loses its mechanical enhancement with a sharp decrease in resilient modulus. 相似文献
16.
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
17.
裂缝对膨胀土抗剪强度指标影响的试验研究 总被引：11，自引：1，他引：10
基于室内直剪试验,测定了膨胀土经历干湿循环后的抗剪强度指标。试验基本反映了膨胀土在干湿循环过程中裂缝的开展现象,揭示了正是由于裂缝的开展使膨胀土强度降低。结果表明,无论是黏聚力还是内摩擦角随裂缝的开展,都会产生一定程度的衰减,相比之下,裂缝对黏聚力的影响更加突出,对其取值也应更为谨慎。膨胀土的抗剪强度随裂缝的开展而衰减的规律符合双曲线模式,提出反映膨胀土抗剪强度随干湿循环次数增加,实际上是随裂缝的开展,而降低规律的经验公式。工程实际中膨胀土的抗剪强度反映的是包含各种裂隙的土体复合强度,因此在设计中,强度参数的取用应以考虑裂隙作用的土体强度为基本依据。所建议的方法可以使今后研究膨胀土裂隙的发生、发展对抗剪强度的影响变得相对简单,具有可操作性。 相似文献
18.
膨胀土裂隙图像处理及特征提取方法的改进 总被引：2，自引：0，他引：2
裂隙特征作为膨胀土裂隙研究的基础,其定量化描述有助于进一步研究裂隙对膨胀土工程性质的影响。以膨胀土平面裂隙为研究对象,使用数码摄影获取膨胀土裂隙图像,通过优化和改进裂隙图像处理方法及裂隙特征提取方法,获得膨胀土裂隙的各特征参数。对于裂隙图像处理方法,采用改进的局部阈值二值化方法,相比大津法能更好地将裂隙和背景区分开来,而通过标记连通区域的方法有效去除了裂隙二值图像中全局分布的细小杂点,同时,利用闭运算填充了裂隙图像中细小的孔洞和缺口,上述处理方法使裂隙二值图像更清晰可靠。对于裂隙特征提取方法,基于对裂隙端点和交点的快捷识别能力,选择了查找表方法作为裂隙条数统计的基础;改进了端点识别算法以去除毛刺,提高了裂隙长度统计的精度;采用改进的最小外接矩形算法进行裂隙宽度的统计,提高了计算精度,节省了计算时间;尝试采用玫瑰花图进行裂隙方向统计,更直观明了地分析裂隙方向及条数的变化规律。 相似文献
19.
膨胀土湿干胀缩裂隙演化及其定量分析 总被引：2，自引：0，他引：2
膨胀土是一种分布广泛且具有明显胀缩性的裂隙土,其裂纹萌生及裂隙扩展会受到诸多因素的影响。此试验利用基于MATLAB开发的图像处理与裂隙定量分析程序,研究了膨胀土裂隙开展的尺寸和温度效应。制备25个不同初始状态的膨胀土泥浆试样,利用拍照台对其失水收缩过程中试样表面裂隙演化过程以及对应含水率进行记录。运用裂隙定量分析程序,分别对两类效应单独作用、耦合作用下的膨胀土裂隙度 、长径比C、裂隙平均宽度 、分形维数值等指标进行定量化分析发现：膨胀土裂隙的分形维数值具有较好的稳定性,其指标仅受试样厚度轻微影响,分形维数与含水率ω的关系呈近似对数曲线;在失水收缩过程中膨胀土最终裂隙指标主要受到试样厚度的影响,表面尺寸对裂隙长径比、宽度最终值也有一定影响,温度影响主要体现在促使裂隙更早、更快的发育并稳定,对最终指标影响相对不明显,影响显著性顺序为：厚度>表面尺寸>温度;此外还对膨胀土失水收缩开裂过程机制进行分析,进一步研究膨胀土的裂隙发育以及两类效应对其裂隙扩展的影响规律。 相似文献
20.
Suffusion involves fine particles migration within the matrix of coarse fraction under seepage flow, which usually occurs in the gap-graded material of dams and levees. Key factors controlling the soil erodibility include confining pressure (p′) and fines content (Fc), of which the coupling effect on suffusion still remains contradictory, as concluded from different studies considering narrow scope of these factors. For this reason, a systematical numerical simulation that considers a relative wide range of p′ and Fc was performed with the coupled discrete element method and computational fluid dynamics approach. Two distinct macroresponses of soil suffusion to p′ were revealed, ie, for a given hydraulic gradient i = 2, an increase in p′ intensifies the suffusion of soil with fines overfilling the voids (eg, Fc = 35%), but have negligible effects on the suffusion of gap-graded soil containing fines underfilling the voids (eg, Fc = 20%). The micromechanical analyses, including force chain buckling and strain energy release, reveal that when the fines overfilled the voids between coarse particles (eg, Fc = 35%) and participated heavily in load-bearing, the erosion of fines under high i could cause the collapse of the original force transmission structure. The release of higher strain energy within samples under higher p′ accelerated particle movement and intensified suffusion. Conversely, in the case where the fines underfilled the voids between coarse particles (eg, Fc = 20%), the selective erosion of fines had little influence on the force network. High p′ in this case prevented suffusion. 相似文献