【作者】 张锐；

【导师】 杨和平；

【作者基本信息】 长沙理工大学 ， 道路与铁道工程， 2005， 硕士

【摘要】 膨胀土是一种因环境干湿交替作用而发生体积明显膨胀(收缩)、强度剧烈衰减而导致工程变形破坏且含有较多膨胀性粘土矿物的非饱和土。堑坡的滑坍及治理是膨胀土地区公路建设的最大技术难题。除了物质成分及土质内因外,干湿循环作用、尤其降雨入渗后土体膨胀、强度衰减是造成边坡滑坍的主要原因。因此,土的抗剪强度特性成了当前非饱和土研究的热门话题。由于非饱和土研究仍处于“简单”阶段,确定强度特性的试验还存许多待完善的地方。为此,以宁明膨胀土为对象,本文较系统并有针对性地开展了非饱和土强度特性试验研究。 首先从成因类型、分布特征以及微观结构方面分析了宁明膨胀土的特征,总结了南友路膨胀土路堑边坡破坏规律和原因。针对干湿循环对膨胀土强度的影响和已有试验研究的不足,设计并开展了模拟实际工况(荷载作用和含水量变化范围)的干湿循环直剪试验。得到有荷条件下膨胀土抗剪强度随着干湿循环的变化规律,并发现荷载对土的胀缩幅度和强度衰减有明显抑制作用。 吸力对土的力学性状有重大影响,是非饱和土研究的核心问题。尽管已有研究成果给出了吸力与吸附强度的关系,但均没考虑土体在吸湿和脱湿路径下强度的差异。利用先进的GDS非饱和三轴系统,本文开展了此项研究。结果表明宁明膨胀土的吸力与吸附强度之间的关系是非线性的,一定的围压作用,吸湿和脱湿路径下的强度有差异但不明显,由此提出宁明非饱和膨胀土有效应力强度理论公式。试验过程中还发现已有GDS系统的不足,并提出相应的改进措施。 由于非饱和土强度参数的获取需用到高精的设备,且试验难度大、费资耗时,妨碍了非饱和土理论在工程中的应用,而包含了吸附强度的总强度指标也能反映非饱和土的强度特性且易于获取。为此,研究了用常规直剪试验仪确定非饱和膨胀土总应力强度指标的方法,得到了宁明膨胀土抗剪强度指标随饱和度、含水量的变化规律,并探讨了膨胀土路堑边坡稳定性分析中的参数取值方法。 全文抓住干湿循环、荷载和吸力三个影响非饱和膨胀土强度的主要因素,遵循理论联系实际的原则来开展宁明膨胀土强度特性试验研究,其目的是获取合理的强度参数用于南友路膨胀土路堑边坡稳定性分析。更多还原

【Abstract】 Expansive soils is a kind of unsaturated soils which contain lots of swelling clay minerals, and usually make structures deformate and destroyed with its strenghth decease sharply as swelling and shrinkage due to the change of its water content in the fluence of weather. The slide of slope is the biggest problem during the construction of road in the regions of expensive soils. Including of inner factors that is the diffirence of minerals content, the effect of wet-dry cycling, especially the swelling of soils with the seepage of the rainfalls and the attenuation of shear strength are the main reasons of slide of expansive soils slope. Therefore the research on the characteristic of shear strength of expansive soils becomes the hot topic in the study on unsaturated soils which is still in the "simple" stage. The tests on the characteristic of strength still have lots of problems which need to be solved. Therefore this thesis systemicly carried out the test on characteristic of shear strength of Ningming unsaturated expansive soils.Firstly the thesis analyse the features of Ningming expansive soils from its type of origins and distributing as well as its fabric and structure, also studied the rules and reasons of slide of expansive soils cut slope of Nanyou expressway. Considering the influence of wet-dry cycling on strength of expansive soils and the shortcoming in the current reaserch on that, the thesis designed and done a direct shear test of wet-dry cycling which simulates the in-site situation, the effect of upper load and the range of change of water content. The variation regularity of the sheat strength index changing with the times of wet-drying cycling under upper loads was gotten in the test, it was also found that the upper load have the obvious restraining to the swelling-shrinkage deformation and the attenuation of shear strength.The suction has the very important influce on the strength behavior of soils, which is the core in the research on unsatured soils. Kinds of relationships between suction and suctional strength were shown in many research papers, but the difference of suctional strength in desorption and absorption of moisture is not considered in those papers. The thesis stuied on the difference using advanced GDS unsatured triaxial testing system. The result shows that the relationship between suction and suctional strength is unlinear, the difference of suctional strength in the two paths that desorption and absorption of moisture is not obvious under a certain cell pressure. According to the result of triaxial test, a shear strength formula of ningming unsaturated expansive soils is put forward. In the test, the shortcomings of GDS unsatured triaxial testing system was also found, the corresponding improvements are also proposed.The behavior of unsaturated soils is complex, and determining its shear strengthparameters need expensive and high-precision instruments, and the test is also very difficult which need lots of time and effords, all those make the theory of unsaturated soil mechanics hard apply to the engineering practice. However, the total strength including suctional strength can also reflect the feature of unsaturated expansive soil strength, and is easy to be obtained. Therefore the method of determining total shear strength of unsaturated expansive soil with conventional direct shear apparatus has been studied, the rule that total shear strength changes with saturation degree and water content has been acquired, meanwhile, the approach of how to choose the strength parameters in the analysis of expansive soil cut slope stability was discussed.The whole thesis focus on three main factors, wetting-drying cyclings, upper load and suction which inflences on the strength of unsaturated expansive soils, and follow principle that theoty should link with practice to carry out testing study on the characteristic of strength of ningming unsaturated expansive soil with the aim making the reasonable parameters applied to the stability analysis of expansive soils cut slope in construction of nanyou expressway.更多还原