【作者】 刘辉；

【导师】 陈昌富； 刘齐建；

【作者基本信息】 湖南大学 ， 岩土工程， 2008， 硕士

【摘要】 软土是一种极其复杂的工程材料,其特殊的物质成分和复杂的结构决定了软土复杂的工程特性。在传统的土力学研究中,土被假定为弹性体或者弹塑性体,然而,无论是线性弹性体还是非线性的弹塑性体,其本构关系都是应力与应变两者之间的关系,与时间无关。而事实上,自然界土体的应力应变关系与时间紧密相关,因而在土体的本构关系中加入时间因素极为必要。这种包括应力、应变和时间三者在内的本构关系就是基于粘弹塑性理论而建立的土的流变力学。越来越多的工程实例表明,岩土很多工程的破坏都跟软土流变有关。因而,研究软土的流变特性具有重要的理论价值和实践意义。正如土的本构关系在土力学中的重要性,土的流变本构关系也是土流变研究的关键所在。因此,本文首先总结了以往研究软土流变本构模型的各种理论,分析了理论模型和经验模型的构造及其优缺点。针对软土流变的非线性,建立一个简化的半理论半经验的流变本构组合模型,用理论模型描述流变的线性部分,用经验模型描述软土流变的非线性部分,并把它应用于上海淤泥质粘土的流变分析中。其次,引入经典的BP神经网络,利用人工神经网络超强的非线性映射能力和容错能力,根据广东江门软土蠕变试验结果,建立广东江门软土流变的网络本构模型,既克服了以往分别按各分级载荷下蠕变试验数据拟和出蠕变本构模型使用不便的缺点,又克服了蠕变本构关系式难以合理构造的困难,并通过上海软土蠕变试验的进一步验证,具有可考虑因素多、拟合精度高、泛化预测能力强、适应性好等特点。最后,针对目前路基沉降计算和预测存在的困难和缺陷,引入了考虑流变的有限元计算方法,通过MSC.Marc/Mentat有限元软件,对杭州绕城高速公路的路基沉降进行了考虑流变和不考虑流变两种方案的有限元分析。结果表明,考虑软土流变的计算方案更符合路基实际沉降规律,在软土地基沉降计算中,特别是工后沉降,考虑软土的流变特性是非常必要的。更多还原

【Abstract】 Soft clay is an extremely complex engineering material, it has complex engineering properties for specific substance components and complex structure. In the traditional research of soil mechanics, soil is generally presumed to be elastic or elastic-plastic body. But whether to be linear elastic or to be nonlinear plastic, its constitutional relation is only the function of stress and strain and has nothing to do with the time. In fact, the stress and strain of soil in nature is closely related to time, so the time element is necessary to be included in the constitutional relation of soft clay. Based on the elastic-viscoplastic theory, the constitutional relation which contains stress, strain and time is called rheological mechanics of soil. An increasing number of projects show that many geotechnical engineering failures are related to rheology of soft clay, therefore it has great theoretical value and practical meaning to study the rheological properties of soft clay.As the importance of constitutive relation of soil on studying soil mechanics, the rheological constitutive relation is also important for studying soil rheology. Therefore all kinds of traditional theories of studying the rheological constitutive model of soil are systematically summarized in the text firstly, then, the merits and demerits of theoretical model and empirical model analyses. According to rheological nonlinearity of soft clay, the text put forward a simplified rheological constitutive model of combining theories with experiences, the theoretical model is used to describe the linear part of rheology and the empirical model is used to describe the nonlinear part of rheology. The model is successfully used to describe the rheology of shanghai muddy clay later. Secondly, introducing the BP neural network and according to the creep data of laboratory direct shear experiment of jiangmen soil, the text build a network rheological constitutive model of jiangmen soil for its strong nonlinear mapping ability and fault-tolerance ability, which can avoid disadvantages of that traditional rheological constitutive models built under each level loading are impractical and a necessary complex constitutive equation is built in order to meeting the fact, then, the model is verified by the direct shear creep experiment of soil of shanghai. it has characteristics of considering more factors, high simulation precision and good generalization ability. Finally, according to difficulties and flaws of calculating and predicting the settlement of subgrade, the paper introduces finite element method which considers rheology of soil. By the MSC.Marc/Mentat software, the settlement of subgrade of loop freeway of Hangzhou is calculated under two schemes, one considers rheology of soft clay, another doesn’t consider rheology of soft clay. The result shows that the calculation scheme of considering rheology of soil is more applicable to practical settlement law of subgrade. In calculating settlement of soft subgrade, especially post-construction settlement, the rheological properties of soft clay is necessary to be considered.更多还原