【作者】 王军；

【导师】 周小文； 龚壁卫；

【作者基本信息】 华南理工大学 ， 岩土工程， 2010， 硕士

【摘要】 膨胀土是一种失水收缩、吸水膨胀的特殊土。气候的干、湿循环常导致膨胀土裂隙发育,进而引起边坡滑动失稳,是膨胀土地区渠道修筑的主要技术难题。研究膨胀土边坡在自然气候影响下的胀缩开裂特性具有非常实际的意义。为此,本文以南水北调中线工程建设为背景,开展了膨胀土干湿循环条件下的开裂特性研究。(1)基于图像灰度化及二值化的数值处理技术以及在膨胀岩土裂隙率概念的基础上,提出了膨胀岩土裂隙的定量描述方法。在南水北调中线新乡潞王坟试验段进行了膨胀岩土裂隙观测试验,定量分析了膨胀岩土边坡在干湿循环中的裂隙的变化规律及其与含水率的相关关系,分析表明:膨胀岩土裂隙的发育与天气变化密切相关,随着干湿循环的发展,裂隙的密度和裂隙率逐渐增加,利用Mat lab数字图像处理方法得到的裂隙率可以较好地描述裂隙的发育程度。(2)通过开展室内原状膨胀土的干湿循环试验,以及CT扫描试验,研究膨胀土的裂隙开展发育特性,以及膨胀土强度随裂隙开展的变化规律。结果表明:在干湿循环条件下,膨胀土原状样粘聚力一次干湿循环次数后显著减小,随后的干湿循环变化不明显,呈现波动的现象;膨胀土剪切强度与试样裂隙率成线性递减关系。(3)通过开展室内重塑膨胀土的干湿循环试验,以及不同应力水平的直剪试验,利用矢量图像处理方法得到直剪试样裂隙的裂隙率,在此基础上研究重塑膨胀土的裂隙开展发育特性,以及膨胀土强度随裂隙开展的变化规律。结果表明:重塑膨胀土裂隙率随干湿循环增加而增加,二者呈线性增长的关系;重塑膨胀土的强度指标随裂隙率的增加而降低,二者呈线性递减关系;重塑膨胀土的强度指标的变化受应力水平的影响,随着干湿循环的次数增加,低应力条件下,重塑膨胀土内摩擦角变化显著,而粘聚力值较小,变化也较小;高应力条件下,重塑膨胀土粘聚力变化显著,而内摩擦角变化较小。更多还原

【Abstract】 Expansive soil is a kind of special soil which will commit to hazards to engineering projects due to the huge dilation and collapse of its volume when this kind of soil comes to wet-dry action caused by the alternative weather. The failure of expansive soil slope is the major technical problem in constructing irrigation ditchs in expansive soil areas. Wherefore, the study on the collapsing and cracking characteristics of expansive soil under the influence of natural climate has a great significance in engineering. Thus, based on the constructing of South-to-North Water Transfer Project Central Route, the study on cracking characteristics of expansive soil under the dry-wet action cycle has been proceeded.(1)Based on numerical processing technology of image grayscale and binarization and the concept of crack degree, the calculation method of which on expansive rock(soil) are presented. The dry-wet cycle tests are carried out in situ of Luwangfen test section, South-to-North Water Transfer Project Central Route, the tests focus on the observations of development changes in cracks and soil moisture changes. According to the results in the tests, the variation law of crack width in expansive rock slope and its relationship with the correlation between moisture content during the dry-wet cycle test are quantitatively analyzed, also the variation law of crack degree is investigated. The development of crack on expansion rock (soil) is closely related to changes in the weather, with the development of wet and dry cycles, the density of cracks and crack degree gradually increase. By using the Mat lab digital image processing methods, the crack degree can be used to effectively describe the growth and development of cracks on expansive rock.(2)By developing the dry-wet cycle test and CT scan test on undirturbed expansive soil in the laboratory. These studies have been preceded, as follows:I the developing characteristics of cracks on undisturbed expansive soilII the variation laws of strength of undisturbed expansive soil as the cracks developingThe results of the tests turned out that the cohesion of undisturbed expansive soil greatly deceased as the first dry-wet cycle occoured, it did not change significantly as the number of dry-wet cycle increased, however, fluctuated. The shear strength of undisturbed expansive soil was liner decrease to the final crack degree of the sample when it failed during the tri-axial test.(3) By developing the dry-wet cycle test and direct shear test on compacted expansive soil in the laboratory and employing the vector diagram technology, these studies have been preceded, as follows: I the developing characteristics of cracks on compacted expansive soilII the variation laws of strength of compacted expansive soil as the cracks developingThe results of the tests turned out that the crack degree of compacted expansive soil greatly increased as the number of dry-wet cycle increased, both were liner increase to each other. The indicator of shear strength of compacted expansive soil greatly decreased as the final crack degree of the sample increased. Both were liner decrease to each other. The indicator of strength of compacted expansive soil was under the influence of stress level. As the crack degree of compacted expansive soil increased, under low-stress conditions, the angle of friction changed significantly, while the cohesion changed little and its value was small too; under high-stress conditions, however, the cohesion changed significantly, while the friction angle changed little.更多还原