【作者】 吴仕帆；

【导师】 闫澍旺；

【作者基本信息】 天津大学 ， 岩土工程， 2009， 硕士

【摘要】 真空预压法作为一种有效的软土地基加固处理方法,具有很多优点,已经广泛运用于港口码头、机场、高速公路、仓库等工程的软基处理中。对于真空预压法的固结机理和加固效果,国内外众多学者和工程师已经做了大量的研究工作,得到了很多有意义的研究成果。但对于吹填土地基的真空预压加固过程研究相对较少。本文拟在总结已有研究成果基础上,对真空预压法加固吹填土地基进行了研究,并运用大型通用有限元软件ABAQUS对加固过程进行了有限元模拟。吹填土地基是天津滨海新区围海造陆的主要地基形式,与天然地基不同的是,吹填土层和上覆填土层的存在改变了原来地基的应力状态,使原天然地基在吹填土和填土的有效重力作用下产生附加荷载,而吹填土本身又为欠固结土,在真空预压加固前,土体中存在尚未消散的超孔压。所以吹填土地基固结过程与正常固结土存在一定的差别,吹填土地基在真空预压过程中的沉降是由吹填土有效自重和真空荷载共同作用下产生的。本文结合吹填土地基的特性,阐述了真空预压法的机理,深入探讨了真空预压土体变形、强度变化、有效加固深度以及加固区地下水位变化等问题。在对真空预压加固机理研究的基础上,根据试验研究了竖向排水体中的负压分布规律;分析吹填土地基各土层的受力状态,对吹填土地基中尚未消散的超孔压进行了等效处理,提出吹填土地基中超孔压的计算方法。结合工程实例,以Biot固结理论为基础,利用ABAQUS有限元软件对真空预压进行了数值模拟,模拟过程中先将塑料排水板等效为砂井,然后通过固结度等效原则,调整土体渗透系数,将轴对称砂井地基转化为平面砂墙地基处理。通过数值模拟研究了吹填土地基的孔压、沉降和侧向位移的变化规律,计算结果与实测值较吻合。作为对真空预压新工艺的探索,本文设计了可控通气真空预压试验,对常规真空预压的排水系统做了改进,增设可控通气装置,进行室内试验。将试验结果与常规真空预压进行对比,阐述了可控通气真空预压法加固机理。更多还原

【Abstract】 Vacuum preloading is an effective method to improve the soft clay foundation. It has been used in many foundation treatment projects, such as harbor yard, airport, express highway, warehouse and etc. Lots of scholars and engineers have done research works about it and got many meaningful results. Nevertheless, there are little study on using the vacuum preload to improve reclaimed soil. Base on the existing research results, this paper make a study on it and do a simulation of the improvement process with the help of finite element software ABAQUS.Reclaimed soil is a main type of foundation in Tianjin Bin Hai new district reclamation project. The reclaimed soil foundation is newly formed, dredger fill layer and filled layer change the stress state of the native foundation, as a result, the additional load on the foundation is including the gravity of filled soil and the excessive pore pressure inside the dredger fill layer. This additional load and the vacuum load should be both considered in the calculation of the settlement. Combined with the properties of reclaimed soil foundation, this paper described the mechanism of vacuum preloading method and discussed the questions about the soil deformation, strength variation, effective reinforced depth and the variation of groundwater level in reinforcement area.Through the analysis of the vacuum preloading theory and experiment research, the delivery of vacuum pressure in the vertical drains has been studied. The calculation of initial pore pressure in the reclaimed soil foundation is also proposed according to every layer’s stress state. The Biot consolidation theory was employed to analyze the vacuum preloading with the help of FEM software ABAQUS. In the simulation process, change the permeability coefficient and convert the axisymmetric condition into equivalent plane strain condition. Comparing the calculating results with the observed data, it is confirmed that the developing trend of settlement and lateral deformation and the variation of pore pressure agree very well with the field data.This thesis presents a new method of vacuum preloading by improving the drainage system. An indoor experiment was made to compare the ventilating vacuum preloading with the ordinary vacuum preloading. On the basis of test data, described the theory of the ventilating vacuum preloading.更多还原