【作者】 刘用海；

【导师】 朱向荣；

【作者基本信息】 浙江大学 ， 岩土工程， 2008， 博士

【摘要】 改革开放以来,随着经济社会的迅猛发展,软土地区城市基础设施、民用建筑等各类工程建设不断涌现,与地基沉降、稳定相关的大量岩土工程问题往往成为制约工程建设的技术难题,对区域性软土开展研究,了解掌握其工程特性对工程建设和经济社会发展具有重要的理论意义和工程实际价值。作为我国首批对外开放的东南沿海重要港口城市和长江三角洲南翼经济中心,宁波区域的发展潜力巨大。对宁波软土的现有研究尚难以满足经济社会快速发展的需求,为此,本文在前人工作基础上,通过调查研究、现场测试、室内土工试验和数值分析,对宁波软土的工程特性和本构模型方面开展研究,主要工作有以下几个方面。一、宁波软土工程特性调查分析。基于收集到的宁波城区地质资料和百余项工程地质勘察报告,归纳整理该区的工程地质概况,总结宁波软土工程特性;采用概率统计方法分析宁波软土各土性参数的空间变异规律,建立各物理力学指标经验关系;根据土的物理力学指标对比,从地质成因、颗粒级配、矿物成分以及微观结构等四个方面分析宁波软土与其它地区软土差异的原因。二、土工试验参数确定方法改进研究。基于Casagrande方法,采用三次多项式和最小二乘法回归拟合压缩曲线,通过数学方法确定先期固结压力,并编写程序实现求解过程;依据时间平方根法求解固结系数原理,采用最小二乘法拟合并从图形学角度分析其计算精度,在已有的商用土工试验数据处理软件平台上开发一个可视化界面程序。三、宁波软土工程特性试验研究。通过室内24组固结压缩试验和70组三轴剪切试验,系统研究宁波软土的应力历史、结构性、蠕变特性以及应力应变影响因素,同时通过相关试验成果的对比分析提出宁波软土工程特性的特点。四、宁波软土本构模型选取比较研究。由室内试验提供Mohr-Coulomb、Drucker-Prager以及修正剑桥三种模型的计算参数,采用有限元软件ABAQUS进行数值计算,对比分析数值计算结果与试验测试数据,确定修正剑桥模型更适合宁波软土,并分析该模型中计算参数的敏感度。五、宁波软土本构模型研究。引入结构损伤变量,在沈珠江提出的岩土损伤力学理论和修正剑桥模型基础上建立扩展的弹塑性损伤模型及其参数确定方法;结合蠕变试验,引入滞后塑性变形概念,将非弹性应变分为瞬时塑性应变和滞后塑性应变,建立扩展的宁波软土弹粘塑性本构模型及其参数确定方法,其瞬时塑性应变分量采用修正剑桥模型求取,滞后塑性应变分量包括体积蠕变和剪切蠕变两部分,分别采用Taylor次固结体积蠕变模型和Mersi剪切蠕变模型;介绍宁波软土弹塑性损伤模型、弹粘塑性模型在ABAQUS有限元程序平台上的UMAT子程序开发流程。六、宁波软土弹塑性损伤模型应用研究。采用所开发的弹塑性损伤模型UMAT子程序,对室内固结压缩试验和某堆载预压试验工程进行数值分析,对模型开展应用研究。更多还原

【Abstract】 With the rapid economic development since China embarked on the policy of reform and opening-up, various kind of projects such as urban infrastructures and civil architectures have been set up in soft clay areas. However, a large number of problems in Geotechnical Engineering, such as foundation settlement and stability, become the technical obstacle and restrict project construction at the same time. Therefore carrying out the study on property of territorial soft clay would have significant theoretical and practical value for project construction and economic development.Ningbo, as one of the first opening-up important seaports, which locates at southeast coastland and is the economic center in the south area of Yangtze River delta, has huge potential for development. However, previous research about Ningbo soft clay couldn’t meet the demands for rapid economic development. For this reason, on the basis of the former researches, the thesis studied on engineering property and constitutive model for Ningbo soft clay by adopting methods of investigation, field measurement, laboratory testing and numerical analysis. The main works are as follows:Firstly, the thesis investigated and analyzed the engineering property of Ningbo soft clay. Based on the collected geologic data of Ningbo area and engineering geologic investigation reports from hundreds of projects, work results such as project geology of Ningbo, spatial variability laws of soft clay property parameters by means of probability statistical method, establishing experiential formulas between physico-mechanical indexes and summarizing engineering property of soft clay. Otherwise, the reasons caused the difference between Ningbo soft clay and other areas were analyzed from the points of geological origin, mechanical composition, mineralogical composition and micro-structure.Secondly, the thesis improved the determination methods of Geo-testing parameter. Based on the theory of Casagrande method, by adopting cubic polynomial and least square method to fit the compression curve, the preconsolidation pressure was determined through mathematical method and achieved the inquiring process by program. Besides, based on the theory of square-time method to acquire consolidation coefficient, by adopting least square method to fit the test curve and from the point of graphics to analyze the accuracy, a visual program was provided on the platform of commercial software.Thirdly, the thesis studied on engineering property of Ningbo soft clay by experiments. Based on the 24 consolidation tests and 70 triaxial shear tests, work results- such as stress history, structural property, creep property and influence factors affect the stress-strain relation were systematic studied. Meanwhile, specialties of Ningbo soft clay were pointed out by contrast with experiment results of others.Fourthly, the thesis studied on contrast of select constitutive model for Ningbo soft clay. Providing computing parameters of models such as Mohr-Coulomb model, Drucker-Prager model and modified Cambridge model by means of laboratory test, and adopting the program of ABAQUS to have numerical computation, conclusion was draw that modified Cambridge model was fit for Ningbo soft clay by compared the numerical computation results with actual measurement results. Besides, sensitivity of computing parameter in modified Cambridge model was analyzed.Fifthly, the thesis studied on constitutive model for Ningbo soft clay. For describing the structural property, by importing structural damage invariable and combined Shen Zhu-jiang theory of damage mechanics for geological materials with modified Cambridge model, an enlarged elasto-plastic damage model for Ningbo soft clay was presented and determining methods for parameters of this model were also provided. Meanwhile, for describing rheologic property, by combining the creep test and introducing the concept of delayed plastic deformation, thus, inelastic strain was divided into an instantaneous plastic part and a delayer visco-plastic part, an enlarged elasto-viscoplastic model was presented and determining methods for parameters of this model were also provided. Thereinto, instantaneous plastic part was acquired by modified Cambridge model and delayed plastic part includes volumetric creep and deviatoric creep, and the former is acquired by Taylor’s secondary compression law, while the latter adopted Singh-Mitchell law. Furthermore, based on the platform of ABAQUS program, development process for UMAT subroutine program of elasto-plastic damage model and elasto-viscoplastic model were introduced.Lastly, the thesis studied on the application of elasto-plastic damage model for Ningbo soft clay. By adopting UMAT subroutine program of elasto-plastic damage model, study on application of this model was carried out through numerical analysis from the aspects of consolidation test and surcharge preloading test.更多还原