真空预压在软基处理中的应用及变形分析

发布时间：2018-05-29 14:41

  本文选题：软土地基 + 真空预压　； 参考：《华南理工大学》2014年硕士论文

【摘要】：随着我国经济的快速发展，工程建设活动也越来越多，特别是在沿海以及内陆江河湖泊地区进行工程建设时经常会遇到软土工程地质，给工程建设带来麻烦，因此需要对软土地基进行处理。 本文在前人调查研究工作以及工程实例的基础上，对真空预压法处理软土地基的地基变形展开研究工作，探索真空预压地基计算沉降的合理方法，并采用有限元进行模拟，主要内容和研究成果如下： （1）归纳总结了我国软土的成因类型、分布特点以及各种处理技术的优缺点。我国软土分布较广，成因类型较多，从北到南，自东至西都有软土的分布，我国软土分布总体上呈现“北强南弱、依次变化”的特点。目前，现有的软土地基的处理方法，从手段上可分为两大类：一类是土质改良法；另一类是复合地基法。土质改良法是从改善原地基土体物质性质着手，提高土体强度、压缩特性等等，主要手段有排水固结、换土垫层等。复合地基法是不改变原土体的性质，在地基中构筑复合地基，使土体和桩体共同承担荷载。 （2）在前述内容的基础上，详细介绍真空预压法的设计、施工及监测方案。以珠海某口岸工程案例为基础，根据场地软土的性质，进行处理方案的比选，最终选择了真空预压法处理软土地基，，并采用监测手段获得真空预压过程中的地基的变形数据，以便于通过数据对真空预压地基的变形规律进行研究。 （3）通过对观测得到的大量数据进行分析，发现地基有较大的沉降量，前期沉降较快，后期较慢，大部分沉降发生在前三个月。其中淤泥层的压缩量占总沉降量的70%~89.3%，其抗剪强度有较大幅度提高，在抽真空的过程中地基中不同深度的孔隙水压力有不同程度的下降。地基加固区周围出现了断断续续的环形裂缝，说明地基在真空预压的过程中会产生向加固区内的收缩变形。真空预压法对塑料排水板深度范围内土体的性质有较大的改善，特别是对淤泥层的改善较大。 （4）在实测数据的基础上，采用等效堆载法、对数曲线法、负压渗流场法、有效应力法、真空度差值法及有限元法进行了计算。将计算结果与实测对比发现：规范推荐的沉降计算方法仍是较实用的方法，但计算结果比实测要小。采用平面应变有限元法对真空预压地基进行变形分析，有限元计算结果与实测较接近，有一定的可靠性，可作为一种计算方法之一。同时对影响真空预压效果的影响因素进行了分析，分析结果表明：膜下真空度大小、塑料排水板深度、间距对工程有较大影响。采用双曲线拟合沉降观测数据，得到地基的最终沉降量，以此计算地基的固结度在80%以上，满足设计的要求。因此塑料排水板要打设到设计处理软土层的层底，间距不宜过大，但由于井阻的作用，真空度的影响深度有限，塑排深度过大会造成不必要的浪费。
[Abstract]:With the rapid development of China's economy, more and more engineering construction activities, especially in the coastal and inland river and lake areas, often encounter soft soil engineering geology, which brings trouble to the construction of the project, so it is necessary to deal with the soft soil foundation.
On the basis of previous research work and engineering examples, this paper studies the deformation of soft soil foundation treated by vacuum preloading method, and explores a reasonable method for calculating settlement of vacuum preloading foundation, and uses finite element method to simulate, the main contents and research results are as follows:
(1) the genetic types and distribution characteristics of soft soil in China and the advantages and disadvantages of various processing techniques are summed up. The distribution of soft soil in China is wide and the genetic types are more, from north to South and from the east to the west, the distribution of soft soil from the east to the west, the distribution of soft soil in China is characterized by the characteristics of "the weak north and the South weak, the second change" in China. At present, the existing soft soil foundation treatment Methods can be divided into two categories: one is the soil improvement method, the other is the composite ground method. The soil quality improvement method is to improve the physical properties of the original soil, improve the strength of the soil, the compression characteristics and so on. The main means are the consolidation of the soil and the soil cushion, etc. the composite foundation method is not changed the nature of the soil and is constructed in the foundation. The composite foundation is constructed to make the soil and pile share the load.
(2) on the basis of the foregoing content, the design, construction and monitoring scheme of vacuum preloading method are introduced in detail. Based on the case of a port engineering in Zhuhai, according to the nature of the soft soil of the site, the comparison and selection of the treatment scheme are carried out, and the vacuum preloading method is selected to deal with the soft soil foundation, and the change of the foundation in the vacuum preloading process is obtained by the monitoring method. Shape data are used to study the deformation rules of vacuum preloading foundation through data.
(3) through the analysis of the large amount of data obtained from the observation, it is found that the foundation has large settlement, the early settlement is faster and the latter is slower, most of the settlement occurs in the first three months. The compress of the silt layer accounts for 70%~89.3% of the total settlement, and its shear strength is greatly improved, and the holes of different depths in the foundation of vacuum extraction are in the process of vacuuming. The gap water pressure decreases in varying degrees. The intermittent ring cracks appear around the reinforcement area, which indicates that the foundation will produce contraction deformation in the reinforced zone during the vacuum preloading process. The vacuum preloading method has a great improvement in the soil properties in the depth range of the plastic drainage plate, especially the improvement of the silt layer.
(4) on the basis of the measured data, the equivalent loading method, logarithmic curve method, negative pressure seepage field method, effective stress method, vacuum difference method and finite element method are used to calculate. The calculation results are compared with the measured results, and it is found that the standard method of settlement calculation is still a more practical method, but the calculation results are smaller than the actual measurement. The finite element method is used to analyze the deformation of vacuum preloaded foundation. The result of finite element calculation is close to the measurement, and it has certain reliability. It can be used as one of the calculation methods. Meanwhile, the influence factors of vacuum preloading effect are analyzed. The results show that the vacuum degree under film, the depth and distance of plastic drain board are more than that of the engineering. A hyperbolic curve fitting settlement observation data is used to get the final settlement of the foundation, so as to calculate the consolidation degree of the foundation above 80% and meet the requirements of the design. Therefore, the plastic drain board should be set to the bottom of the soft soil layer designed to deal with the ground, but the spacing of the ground is not too large, but the depth of the vacuum degree is limited and the depth of the vacuum is limited and the depth of the plastic drainage is limited due to the effect of the well resistance. The meeting caused unnecessary waste.
【学位授予单位】：华南理工大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU472.33

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