大面积吹填场地中的桩基受力特性及其计算方法
发布时间：2018-09-11 17:49
【摘要】：随着滨海地区经济的快速发展,土地资源日趋紧张,吹填造陆工程越来越多。新吹填场地的地质条件具有浅层新吹填土欠固结、中深部海底沉积层软弱的特征。因此,吹填场地中进行基础工程建设,桩基础受负摩擦力的影响显著,且呈现浅层欠固结土自重固结和下卧层在堆载下压缩沉降的综合作用。对新吹填场地中的桩基受力特性开展研究,揭示综合效应下的桩基负摩擦力作用机理,评估其负摩擦力发生发展过程,并提出相应的计算分析方法,可以为我国快速发展的填海造地区域的工程建设提供理论和技术支撑,不仅有很强的科学意义还有显著的实用价值。本文结合实际工程,通过现场试验、数值模拟等方法研究了大面积吹填场地中桩基的受力变形特性,并总结出吹填场地中单桩负摩擦力受力模式和简化计算方法,取得了如下成果:(1)对大面积吹填场地中桩基受力特性进行长期原位测试,分析桩身负摩擦力的产生和发展规律。采用滑动测微计对两根试验桩的桩身应变进行长期监测,从而得到桩身轴力分布特征和桩侧摩阻力变化情况。现场试验结果表明,新吹填场地中的桩基在施工完成后开始逐步受到负摩擦力作用,其桩身轴力和中性点深度随时间不断增大,沉桩完成1年后仍未稳定。桩身浅部受到明显的负摩擦力作用,其中吹填土层内的负摩擦力随深度的增加而增大,下卧原状土层内的负摩擦力随深度减小。(2)考虑饱和土流固耦合的Biot固结理论,对吹填场地中桩基的长期受力特性进行数值模拟分析。根据试验桩的静载荷试验结果进行反分析,确定数值计算的土层参数参数,并结合地质勘察报告和试验桩现场试验结果进行验证。应用验证后的计算参数对两根试验桩负摩擦力的长期发展性状进行预测评估。计算结果表明,该吹填场地中桩基的轴力和中性点深度在沉桩3年以后可基本达到稳定,稳定状态下的负摩擦力分布仍表现为:吹填土层内随深度增大、下卧原状土层内随深度减小。(3)考虑桩基设计和使用的不同工况,应用上述数值方法对吹填场地中桩基受力性状进行参数分析。针对桩顶受力和桩周堆载共同作用下的桩基工作状态,分析了堆载条件和桩长对桩身负摩擦力的影响规律。针对吹填场地的特点,通过参数分析研究了吹填土层厚度和负摩擦力消除措施对桩身受力的影响,并比较了吹填土层和地面堆载作用下桩基负摩擦力的差异,进一步验证了吹填场地中负摩擦力发展和分布特点。(4)根据现场试验和数值分析结果,提出了吹填场地中单桩负摩擦力的简化计算方法。由测试和数值分析考虑到现行规范方法计算吹填土中桩基中性点和最大负摩擦力的结果偏差较大,根据原位测试和数值分析结果提出了简化的桩身负摩擦力分布模式——吹填土层内负摩擦力随深度增加而下卧土层内随深度减小,进而推导出桩基中性点和轴力的计算公式。与规范方法计算结果、数值分析预测结果的比较分析表明,该方法可以简便而准确的确定吹填场地内桩身受力性状,可为工程设计计算提供参考。
[Abstract]:With the rapid economic development in coastal areas, land resources are increasingly tense, and more and more land reclamation projects are carried out by dredger. The geological conditions of new dredger fill sites are characterized by underconsolidation of shallow new dredger fill and weak sedimentary layers in the middle and deep seabed. The comprehensive effect of self-weight consolidation of under-consolidated soil and compression settlement of underlying stratum under surcharge is studied. The mechanical characteristics of pile foundation in new dredger fill site are studied, the mechanism of negative friction of pile foundation under comprehensive effect is revealed, the occurrence and development process of negative friction is evaluated, and the corresponding calculation and analysis methods are put forward, which can be used for rapid development of filling in China. The theory and technology support provided by the engineering construction in the marine area is not only of great scientific significance but also of great practical value. Combining with the practical engineering, this paper studies the stress and deformation characteristics of the pile foundation in the large-area dredger fill site by means of field test and numerical simulation, and summarizes the stress mode of the negative friction of the single pile in the dredger fill site. The main results are as follows: (1) In-situ testing of pile foundation in large-area dredger filling site is carried out for a long time to analyze the generation and development of negative friction of pile body. Field test results show that the pile foundation in the new filling site is gradually subjected to negative friction after construction. The axial force and the depth of the neutral point of the pile increase with time, and the pile is still unstable one year after the completion of pile driving. The negative friction in the undisturbed soil layer decreases with the increase of the depth. (2) Considering the fluid-solid coupling theory of the saturated soil, the long-term mechanical behavior of the pile foundation in the dredger filling site is simulated and analyzed numerically. The results show that the axial force and the depth of the neutral point of the pile foundation in the dredger fill site can be basically stable after three years of piling, and the distribution of the negative friction force in the stable state can be basically stable. (3) Considering the different working conditions of pile foundation design and use, the above numerical method is used to analyze the behavior of pile foundation in the dredger fill site. According to the working state of pile foundation under the combined action of pile top force and pile surcharge, the condition of surcharge is analyzed. According to the characteristics of dredger fill site, the influence of dredger fill thickness and negative friction eliminating measures on pile body force is analyzed and studied by parameter analysis, and the difference of negative friction between dredger fill and ground surcharge is compared, which further verifies the development of negative friction in dredger fill site. (4) Based on the field test and numerical analysis results, a simplified method for calculating the negative friction force of a single pile in a dredged fill site is proposed. Considering the large deviation between the results of calculation of the neutral point and the maximum negative friction force of the pile foundation in the dredged fill soil by the test and numerical analysis, a new method is proposed according to the results of in-situ test and numerical analysis. A simplified distribution model of negative friction of pile body-the negative friction in dredged fill decreases with the increase of depth in the underlying soil layer, and then the calculation formulas of the neutral point and axial force of pile foundation are deduced. The behavior of the internal pile can provide reference for engineering design calculation.
【学位授予单位】：上海交通大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU473.1
本文编号：2237413
[Abstract]:With the rapid economic development in coastal areas, land resources are increasingly tense, and more and more land reclamation projects are carried out by dredger. The geological conditions of new dredger fill sites are characterized by underconsolidation of shallow new dredger fill and weak sedimentary layers in the middle and deep seabed. The comprehensive effect of self-weight consolidation of under-consolidated soil and compression settlement of underlying stratum under surcharge is studied. The mechanical characteristics of pile foundation in new dredger fill site are studied, the mechanism of negative friction of pile foundation under comprehensive effect is revealed, the occurrence and development process of negative friction is evaluated, and the corresponding calculation and analysis methods are put forward, which can be used for rapid development of filling in China. The theory and technology support provided by the engineering construction in the marine area is not only of great scientific significance but also of great practical value. Combining with the practical engineering, this paper studies the stress and deformation characteristics of the pile foundation in the large-area dredger fill site by means of field test and numerical simulation, and summarizes the stress mode of the negative friction of the single pile in the dredger fill site. The main results are as follows: (1) In-situ testing of pile foundation in large-area dredger filling site is carried out for a long time to analyze the generation and development of negative friction of pile body. Field test results show that the pile foundation in the new filling site is gradually subjected to negative friction after construction. The axial force and the depth of the neutral point of the pile increase with time, and the pile is still unstable one year after the completion of pile driving. The negative friction in the undisturbed soil layer decreases with the increase of the depth. (2) Considering the fluid-solid coupling theory of the saturated soil, the long-term mechanical behavior of the pile foundation in the dredger filling site is simulated and analyzed numerically. The results show that the axial force and the depth of the neutral point of the pile foundation in the dredger fill site can be basically stable after three years of piling, and the distribution of the negative friction force in the stable state can be basically stable. (3) Considering the different working conditions of pile foundation design and use, the above numerical method is used to analyze the behavior of pile foundation in the dredger fill site. According to the working state of pile foundation under the combined action of pile top force and pile surcharge, the condition of surcharge is analyzed. According to the characteristics of dredger fill site, the influence of dredger fill thickness and negative friction eliminating measures on pile body force is analyzed and studied by parameter analysis, and the difference of negative friction between dredger fill and ground surcharge is compared, which further verifies the development of negative friction in dredger fill site. (4) Based on the field test and numerical analysis results, a simplified method for calculating the negative friction force of a single pile in a dredged fill site is proposed. Considering the large deviation between the results of calculation of the neutral point and the maximum negative friction force of the pile foundation in the dredged fill soil by the test and numerical analysis, a new method is proposed according to the results of in-situ test and numerical analysis. A simplified distribution model of negative friction of pile body-the negative friction in dredged fill decreases with the increase of depth in the underlying soil layer, and then the calculation formulas of the neutral point and axial force of pile foundation are deduced. The behavior of the internal pile can provide reference for engineering design calculation.
【学位授予单位】：上海交通大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU473.1
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