论文总字数：34365字

摘 要

在工程建设常采用水泥土搅拌桩进行地基处理，比较理想的情况是能够穿过软弱土层使桩端到达硬质土层，进行这样的处理，被认为是有效地控制沉降的一种常见方法。但是随着工程建设的发展，许多工程面对着一种新的特殊地质条件，即深厚软土地基。因水泥土搅拌桩施工设备的限制，使得目前的施工中，很难将深厚软弱土层打穿，此时水泥土搅拌桩的桩端并未到达硬土层，桩体在软土中处于悬浮状态，即形成悬浮式水泥土搅拌桩。

对于悬浮式水泥土搅拌桩复合地基的设计，关键在于对其沉降的计算。由于悬浮式水泥土搅拌桩复合地基设计的特点，复合地基的沉降可分为加固层沉降和下卧层沉降。已有研究表明，发生在下卧层的沉降是悬浮式水泥土搅拌桩复合地基沉降的主要来源。因此，对于悬浮式水泥土搅拌桩复合地基设计而言，对于下卧层沉降的计算相当关键。

基于上述背景，本毕业设计针对对深厚软土地基进行悬浮式水泥土搅拌桩复合地基处理后，下卧层沉降的计算，主要进行了两方面的工作：

通过广泛查阅国内现有规范以及国内外学者在该领域的研究成果，总结了悬浮式水泥土搅拌桩复合地基沉降计算方法。加固层沉降可以使用复合模量法、应力修正法和桩身压缩法进行计算；对于下卧层沉降的计算，比较典型的计算方法则有应力扩散法、等效实体法、应力扩散系数法、改良经验公式法、日本建筑工学会提出的方法和日本Chai等人提出的改良方法等。本文对这些计算方法的计算思路、参数取值以及误差来源等进行了详细的分析。

结合沪苏浙高速公路软基处理工程，使用规范推荐的沉降计算方法，对所取工程试验段进行了设计，并据此确定了既符合工程要求，又能尽可能节约经费和降低施工难度的设计方案；根据所取工程试验段原有的悬浮式水泥土搅拌桩复合地基设计方案，使用所有已介绍的沉降计算方法进行计算，并与实测沉降值进行比较，计算误差值。通过分析比选，本文对所有计算方法的优势、不足之处和适用条件进行了进一步的分析，认为改良经验公式法是更适合本工程试验段的下卧层沉降计算方法。

关键词：水泥土搅拌桩 复合地基 悬浮桩 下卧层 沉降

ABSTRACT

In the engineering construction, cement-soil mixing piles are often used for foundation treatment. Ideally, it is possible to penetrate the soft soil layer to make the pile end reach the hard soil layer. Such treatment is considered as a common method for effectively controlling the settlement. . However, with the development of engineering construction, many projects face a new kind of special geological conditions, namely deep soft ground. Due to the limitation of the construction equipment of cement-soil mixing piles, in the current construction, it is difficult to penetrate the deep soft soil layer. At this time, the pile end of the cement-soil mixing pile does not reach the hard soil layer, and the pile body is suspended in the soft soil. State, that is, the formation of suspended cement-soil mixing piles.

For the design of composite foundation with suspended cement-soil mixing piles, the key is to calculate its settlement. Due to the characteristics of composite foundation design of suspended cement-soil mixing piles, the settlement of composite foundation can be divided into settlement of reinforcement layer and settlement of underlying layer. Studies have shown that the settlement occurring in the lower layer is the main source of settlement of the composite foundation with suspended cement-soil mixing piles. Therefore, for the design of suspended soil-cement mixing pile composite foundation, the calculation of subsidence settlement is critical.

Based on the above background, this graduation project mainly focuses on the following two aspects of the calculation of the settlement of the substratum after the treatment of the composite foundation with suspended cement-soil mixing piles for deep soft ground.

By extensively reviewing the existing domestic regulations and the research achievements of scholars at home and abroad in this field, the settlement calculation method for composite foundation with suspended cement-soil mixing piles was summarized. The settlement of the reinforcement layer can be calculated using the composite modulus method, the stress correction method and the pile compression method; for the calculation of the subsoil settlement, the typical calculation methods are the stress diffusion method, the equivalent solid method, the stress diffusion coefficient method, Improvement of the empirical formula method, the method proposed by the Japan Society of Building Engineers, and the improved method proposed by Chai et al. in Japan. This paper makes a detailed analysis of the calculation methods, parameter values ​​and error sources of these calculation methods.

In combination with the Shanghai-Suzhou-Zhejiang Expressway soft foundation treatment project, using the recommended settlement calculation method of the standard, the design of the experimental section taken is designed, and accordingly it is determined that the project meets the requirements of the project, but also saves money and reduces the construction difficulty as much as possible. Design plan; According to the original design plan of the suspended cement-soil mixing pile composite foundation of the engineering test section, the calculation of all the introduced settlement calculation methods is used to calculate the error value compared with the measured settlement value. Through analysis and comparison, this paper further analyzes the advantages, disadvantages and applicable conditions of all calculation methods. It is believed that the improved empirical formula method is more suitable for the settlement calculation method of the underlying layer of the project.

KEY WORDS：Cement-soil mixing pile, composite foundation, suspended pile, lower layer, settlement

目 录

摘要 I

ABSTRACT II

第一章 绪论 1

1.1研究背景 1

1.2研究现状 1

1.2.1深厚软土地基的特性及危害 1

1.2.2水泥土搅拌桩设计及应用现状 2

1.2.3悬浮式水泥土搅拌桩法复合地基沉降计算研究及应用现状 5

1.3研究内容 7

1.4技术路线 8

第二章 悬浮式水泥土搅拌桩复合地基的沉降计算 9

2.1现有规范关于悬浮式水泥土搅拌桩复合地基的沉降计算 9

2.1.1加固区沉降计算方法 9

2.1.2下卧层沉降计算方法 12

2.2下卧层沉降计算的其它方法 13

2.3本章小结 16

第三章 工程实例分析 17

3.1工程概况 17

3.2 工程地质条件 17

3.2.1全线工程地质条件 17

3.2.2试验段工程地质条件 18

3.3地基处理设计 19

3.4沉降计算与分析 19

3.4.1按规范的沉降计算 19

3.4.2国内外多种沉降计算方法的比选与研究 22

3.5结果分析 28

3.6本章小结 30

第四章 结论与展望 31

4.1 结论 31

4.2 展望 32

致 谢 33

参考文献 34

第一章 绪论

1.1研究背景

在我国，软土分布十分广泛，在许多地区存在着深厚的软土层在，这种地质特点更多的出现在我国的沿海地区。随着经济的发展，我国越来越重视各类基础建设工程，在此类工程地质条件下进行的工程也日渐增加。诸多工程实例表明，深厚软土地基较之一般的软土地基，更容易产生大的沉降。此外，也容易产生其他问题，如路堤的滑移或者失稳。这些问题会对该工程造成很严重的安全隐患。正因如此，对深厚软土地基采取必要的工程措施，确保工程质量，保障工程安全，便十分必要。

软土地基处理的方法中，使用桩土复合地基类处理的方法目前被广泛使用，根据在各类工程中的反馈，该方法取得了不错的效果。而深厚软土地基的最大特点就在于其软土层厚度很大。在目前的工程中，对于深厚软土地基通常采用双向水泥土搅拌桩进行处理。由于搅拌桩桩长的长度有限制，搅拌桩并不能完全打穿软土层，此时桩体悬浮在软土中。处于这种情况下的复合地基，其沉降主要发生在下卧层。因此对于悬浮式双向水泥土搅拌桩的设计与研究关键，就是要对下卧层的沉降做出准确的计算或估算。

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