论文总字数：18498字

摘 要

支护结构的受力分析是基坑设计的重中之重，计算结果的准确性主要取决于分析过程是否与坑周土体所处的应力状态相符。基坑开挖过程中，坑周土体处于侧向卸荷状态，而目前设计计算所用参数均是基于土体在压缩状态下的所得到的力学性能指标，基于该参数计算得到的结果往往与实际不符，需要乘以地方经验修正系数进行校正。为了充分了解基坑开挖过程中坑周土体的应力-应变状态，本文使用TSZ-2型全自动三轴仪对300kPa、500kPa以及700kPa压力下制成的土样的力学性能进行研究，并且利用有限元分析软件对基坑开挖时土体侧向卸荷时的力学性能进行数值模拟。由于应力路径对粉质黏土的强度影响显著，因此研究两种不同应力路径下土样的力学性能显得很有必要。通过比较两种不同应力路径下土的力学性能的差异，给基坑开挖支护结构设计提供参考。研究表明：在相同的情况下，常规三轴固结不排水的抗剪强度大于三轴侧向卸荷时土的抗剪强度，在破坏时，三轴侧向卸荷的轴向应变要小于常规三轴固结不排水剪的轴向应变。另外，还基于渗透试验分析了黏土的固结参数，了解了黏土孔压消散时间长的原因。

关键词：基坑开挖 应力路径 侧向卸荷 三轴实验 渗透

Test and analysis of soil stress around the excavation

Abstract

The stress calculation of the foundation pit is the an important thing during the foundation pit excavation, and learn about the stress of soil around the foundation pit is the most important. Foundation pit excavation is different from loading engineering in that the soil under the state of lateral unloading during excavation. At present, the mechanical property paraments of soil around the pit. The results calculated by this method can generally meet the design requirements of the supporting structure during the excavation of the foundation with the correction of regional experience. In order to fully understand the stress-strain of the soil around the pit during the excavation, the TSZ-2 automatic triaxial instrument was used in this paper to study the mechanical properties of soil samples consolidated under pressure of 300kPa,500kPa and 700kPa,and the finite element analysis software was used to simulated the mechanical properties of the soil during the lateral unloading. By comparing the mechanical properties of soil under two difference stress paths, this paper provides a reference for the design of foundation pit excavation supply structure. The results show that under the same stress conditions ,the shear strength of the triaxial undrained shear is greater than that of the soil under the triaxial undrained shear, and the axial strain under triaxial undrained shear is smaller than that of the conventional triaxial undrained shear under the failure condition.

Key Words: foundation excavation; stress paths; lateral unload; triaxial test; permeate

目录

摘 要 I

Abstract II

第一章 绪论 1

1.1研究背景 1

1.2应力路径研究 1

第二章 实验方案 3

2.1实验土体 3

2.2.1取样 3

2.1.2基本物理性质测定 3

2.2实验方案 3

2.2.1三轴常规压缩实验 4

2.2.2数值模拟 4

2.2.3渗透系数测定 4

2.3实验仪器 4

2.3.1制样装置 4

2.3.2三轴实验仪 5

2.3.3渗透实验仪 5

2.4实验准备工作 6

2.4.1制样 6

2.4.2切样以及饱和 7

第三章 常规三轴试验 9

3.1三轴固结不排水试验 9

3.1.1.仪器自检 9

3.2实验数据导出 10

3.3常规三轴固结不排水数据处理 10

3.3.1应力应变曲线对比 10

3.3.2粘滞力c与内摩擦角 12

3.3.3 应力路径比较 15

第四章 有限元模拟 17

4.1 有限元分析方法 17

4.2 有限元分析模型 17

4.2.1建立部件 17

4.2.2设置材料属性及截面参数 17

4.2.3定义分析步 18

4.2.4定义荷载及边界条件 18

4.2.5划分网格区域 18

4.2.6进入模拟 19

4.3结果处理 19

4.3.1三轴固结不排水 19

4.3.2三轴侧向卸荷 22

4.3.3结果对比 23

第五章 固结参数分析 25

5.1渗透系数测量 25

5.1.1渗透实验 25

5.1.2渗透系数计算 26

5.2固结系数 26

5.2.1固结系数计算 26

第六章 结论 29

参考文献 31

致谢 32

第一章 绪论

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