基于非线性渗流定律的软土一维固结理论研究
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摘要
大量的室内试验和现场沉降观测资料均表明软粘土中的渗流会出现偏离达西定律的现象,然而目前现有的大多数固结理论均采用达西定律来描述土中的渗流,对基于非线性渗流(或称非达西渗流)定律的软土固结理论的研究目前并不多见,尤其是对考虑非达西渗流定律的成层地基非线性固结理论研究更为不足。鉴于此,本文分别基于Slepicka指数形式渗流定律和Hansbo所提出的非达西渗流模型采用有限差分法及半解析法对软土一维线性及非线性固结理论展开较系统深入的研究,详细的分析了考虑非达西渗流的软土一维固结性状。主要的研究内容和创新工作如下:
     1.考虑实际中的变荷载,建立了考虑两种常用的非达西渗流模型的软土地基一维固结问题的控制方程,并分别采用有限差分法和半解析法对其进行数值求解。然后将两种方法计算的固结曲线进行对比,验证了两种数值计算结果的可靠性。在此基础上,详细分析了两种非达西渗流模型中的参数、土层厚度、荷载的大小以及加载速率等对非达西渗流模型下软土地基一维固结性状的影响。2.考虑实际中的变荷载及天然地基的成层性,对考虑两种常用的非达西渗流模型的成层地基一维固结问题展开了系统的研究。首先对考虑两种非达西渗流模型的双层地基
     一维线性固结采用有限差分法进行求解,而对考虑两种非达西渗流模型的多层地基一维线性固结则采用半解析方法进行求解。然后将两种方法得到的双层地基固结曲线进行对比,验证了计算结果的可靠性。进而详细地分析讨论了两种非达西渗流模型中的参数、荷载大小、土层厚度、双层地基上、下土层相对压缩性、相对渗透性以及相对厚度对双层地基固结性状的影响,并给出了考虑两种常用的非达西渗流模型的多层地基一维固结计算实例。
     3.考虑实际中的变荷载及自重应力沿深度的不同分布形式,引入经典的土体孔隙比与渗透系数、土体孔隙比与有效应力之间的非线性关系,对考虑两种常用的非达西渗流模型的软土地基一维非线性固结问题分别采用差分法和半解析法进行求解。将两种方法得到的固结曲线进行对比,验证了数值计算的可靠性。在此基础上,系统地分析了两种非达西渗流模型中的参数、压缩指数和渗透指数的比值、荷载大小、土层厚度、自重应力的分布形式对软土地基一维非线性固结性状的影响。
Numerous experiments and settlement measurements have shown that the water flow in soft soils may deviate from Darcy's law. However, few researches on consolidation theory for soft soils with non-Darcian flow have been reported, especially on non-linear consolidation theory of layed-soil with non-Darcian flow. Therefore, this dissertation systematically studies one-dimensional linear and non-linear consolidation theory with exponential flow law and non-Darcian flow model proposed by Hansbo by finite difference method and semi-analytical method, and one-dimensional consolidation behaviour of soft soils with two common non-Darcian flow models is analyzed in detail. The main original works are as follows:
     1. Considering time-dependent loading in actual engineering, the differential equations governing one-dimensional consolidation with two common non-Darcian flow models are developed, and the numerical solutions are obtained respectively by finite difference method and semi-analytical method. The consolidation curves obtained by both methods are compared, and the reliability of numerical results is testified. On this basis, the influences of parameters in two common non-Darcian flow models, the thickness of soil layer, the value of external loading and the loading rate on consolidation behavior with non-Darcian flow models are analyzed in detail.
     2. Considering time-dependent loading and layered distribution of soils in natural foundation, one-dimensional consolidation theory for layered soils with two common non-Darcian flow models is systematically studied. Firstly the problem of one-dimensional consolidation of double-layered soil with two common non-Darcian flow models is solved by finite difference method, and that of multi-layered soils is solved by semi-analytical method. Then consolidation curves of double-layered soil with two common non-Darcian flow models obtained by both numerical methods are plotted together to show the correctness of numerical results. Further more, the influences of parameters of two common non-Darcian flow models, the value of external loading, the total thickness of double-layered soils, relative permeability, relative compressibility and relative thickness of double-layered soils on the consolidation behavior of the double-layered soils are discussed in detail.
     3. Considering time-dependent loading and different distribution types of self-weight stress and incorporating the nonlinear relationship between void ratio and permeability coefficient as well as that between void ratio and effective stress, the differential equations governing one-dimensional non-linear consolidation with two common non-Darcian flow models are solved by finite difference menthod and semi-analytical method, respectively. The reliability of numerical results is verified by comparing the consolidation curves obtained by both numerical methods. The influence of parameters of non-Darcian flow models, the ratio of compression index to permeability index, the value of external loading, the thickness of soil layer and the distribution type of self-weight stress on nonlinear consolidation behavior with two common non-Darcian flow models are systematically discussed.
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