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路堤荷载下刚性桩复合地基理论与应用研究 【作者】余闯 【导师】刘松玉

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路堤荷载下刚性桩复合地基理论与应用研究水利论文0OI9b O4u2z6X#^4ZA

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【作者】余闯 【导师刘松玉
(e.m l~k#U#h6e"wl?0【作者基本信息】东南大学,岩土工程,2006年,博士

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【中文摘要】 刚性桩复合地基具有施工质量易控制、施工速度快、工后沉降及不均匀沉降小、处理深度大、复合地基承载力大、造价比较适中等优点,在高速公路软基处理中得到了重视,并有初步的应用,但是缺乏系统的理论分析。本文分析了刚性桩复合地基加固高速公路软土地基的应用及研究现状,指出目前需要解决的关键问题。通过理论分析、数值模拟和现场试验对路堤荷载下刚性桩复合地基的性状进行了系统的研究,主要内容如下:(1)首先总结了传统的刚性桩复合地基的研究现状,指出了路堤荷载下刚性桩复合地基和一般建筑物下刚性桩复合地基(复合桩基)的不同之处,分析了加固软土地基的应用现状,提出了路堤荷载下刚性桩复合地基需要解决的问题。(2)利用轴对称的有限元计算模型,分析路堤荷载刚性桩复合地基中不带桩帽和带桩帽刚性桩单桩性状,计算结果表明路堤填料中存在“等沉面”和“土拱效应”的现象;计算结果还显示桩帽尺寸的大小与桩间距之间的比例关系是控制桩体荷载分担的关键因素,而桩端土层性质的变化对其影响不大。利用多拱理论,分别给出了桩间土应力和桩帽上部土体应力的解析解,推导了有加筋材料作用下的桩体荷载分担比的计算公式,同时给出了筋材的应力和变形计算公式,并...更多讨论了桩体荷载分担比随各种因素的影响规律。模型试验和数值模拟的结果验证了本文提出计算公式的正确性。(3)建立了路堤荷载下刚性桩复合地基桩-桩帽-土共同作用的有限层-有限元方程,并编制了相关计算程序。通过典型算例的计算得出了如下主要结论:通过柔性荷载和刚性荷载作用桩土共同作用的对比分析,得出了两种荷载作用的桩帽(承台)下土体反力分布特征有很大的不同,刚性荷载作用下桩帽下土体反力呈现出边上大的典型分布特征,而柔性荷载作用下,土体反力呈现出边上小,中间大的分布特征,特别是在在桩帽上部荷载水平较小的情况下尤为突出;在相同的桩帽荷载作用下,柔性荷载下桩的侧摩阻力的发挥程度要大于刚性荷载下的情况,变形特性也具有相同的特点,且桩帽下土体荷载分担比要小。(4) PTC预应力管桩施工过程中的现场试验表明:海相软土中PTC预应力管桩采用锤击法施工会产生较大的超孔隙水压力。管桩的桩径、桩长以及有无桩靴对孔压及其消散规律都有很大的影响。单桩施工引起的孔压在初期消散较快,其后逐渐缓慢;群桩引起的孔压消散速率则缓慢得多。单桩和群桩施工后不同时间的桩周土体的现场静力触探试验表明,桩体施工后导致桩周具有强结构性的连云港天然沉积土的结构破坏,从而导致桩周土强度的降低,而且该土层强度短期内很难恢复。对典型软土层,锥尖阻力比主要在0.50.9范围内变化。(5)多组PTC预应力管桩静载试验结果的对比分析表明,桩帽对单桩复合地基的承载力有明显的提高作用,增幅达18%。通过静载试验和高应变的对比分析,显示两种测试方法的结果具有相当的一致性。打桩后不同时间的高应变测试结果表明,海相软土中PTC预应力管桩的承载力随时间在增长,且增幅较大,单桩极限承载力增幅均大于50%。总结了路堤荷载下刚性桩复合地基中负摩阻力问题,对土体沉降采用Terzaghi一维固结理论,在假设桩及桩周土体变形规律的基础上得到了桩体轴力和变形的计算公式,与一个工程实例的测试结果具有良好的一致性。结合现场试验结果,提出了连云港地区考虑桩间土强度时间效应的系数μ和桩间土强度发挥度λ的取值范围,给出了合理的路堤荷载刚性桩复合地基承载力的计算方法。(6)从刚性荷载和柔性荷载作用下的刚性桩复合地基沉降不同特性出发,分别提出了桩间土应力减小比法、位移模式法和等沉面法等沉降计算方法。利用所提方法分别对PTC预应力管桩和CFG桩处理的试验段进行了计算,并与实测结果和其它计算方法进行了对比分析,探讨了本文所提方法的合理性和适用范围。(7)探讨加载方式对路堤沉降性状的影响,采用考虑流变的Merchant土体本构模型解释了沉降-时间曲线与加载方式的关系,分析了瞬时加载、线性加载和分级加载情况下沉降的发展规律,在此基础上提出了符合各自沉降和沉降速率变化特征的指数、Gompertz和分段Gompertz预测模型,多个工程实例的预测和分析证明了所提的预测模型的科学性和实用性。从路堤荷载作用下地基的水  还原

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【英文摘要】 The rigid pile composite foundation (RPCF) with individual pile caps combined geosynthetic-reinforcement have demonstrated excellent performance characteristics in ground treatment for highway engineering. RPCF owns technical and economical advantages over other methods, for example , convenient alternating construction, little post-construction and differential settlements, fair consolidation, deep depth of ground improvement, high load capacity and savings of construction time and costs. This type of ground improvement is already taken account into soft ground improvement in highway engineering in China. But it is lack of comprehensive theoretical analysis.The state art of RPCF in soft ground improvement in highway engineering in china is discussed and the key issues are put forward in the paper. Based on the previous researcher’s work , the thesis studied the behavior of RPCF under embankment loads via theoretical analysis, numerical simulation and field test. The main contents are ...更多as follows(1) The state art of conventional RPCF(composite pile foundation)under rigid loads is reviewed, and the different performance of RPCF under rigid loads and embankment loads is pointed out. The problems need to be solved in the paper are brought out.(2) The proposed model is implemented in an axisymmetric finite element code and numerical simulations are made for the behavior of single rigid pile composite foundation without and with cap under embankment loads. The simulated results indicate that“the plane of equal settlement”and“Soil arching effect”exist in embankment fills. The results also show that the proportion of the magnitude of pile cap size and pile spacing is the key factor to control the load distribution between pile caps and soils between piles. According to the vertical force equilibrium, the equations computing the vertical soil stress acted on pile caps and soils between piles are concluded using multi-arch theory. The equation of computing the stress coupled the geosynthetic-reinforcement is also presented and the equations of calculating strain and stress of are obtained. Finally, the factors affecting the ratio of load carried by pile caps are discussed.(3) Using semi-analytic-numerical method of finite layer method and finite element method, the formulation of the interaction among pile-pile cap-soil in RPCF under embankment loads is put forward. The computing program is made for investigating the behavior of RPCF. From the calculated cases of RPCF under rigid loads and embankment loads, it is pointed out that the behavior of RPCF under embankment loads is distinctly different from that under rigid loads. The soil pressure distribution underneath raft under rigid loads is similar with saddle .But under embankment loads,it increases faster the vicinity of the pile than that in the middle and edge of the pile. At the same load level , the friction along pile shaft is larger than that under rigid loads. The settlement is larger and the load carried by soils underneath pile caps is smaller than that under rigid loads.(4)The Prestressed Tubular Concrete Pile (PTC pipe pile) installation using hammering method causes the increase in pore water pressure of surrounding clays, and the maximum excess pore water pressure is nearly 2 times the effective overburden stress in ground soils. Diameter, length of pipe piles and open-ended or close-ended all affect the excess pore water pressure during pile installation. The excess pore water pressure increases with time during pile installation and dissipates with time after installation. The dissipation time of excess pore pressure varies with the time and the distance from the pile. The dissipation rate initially is larger than later. The longer the dissipation time, the closer the distance is. Cone penetration tests were performed on  还原水利论文 ^\0ejU-C#~eU

z*D1PM X~0【中文关键词】 刚性桩复合地基; 软土地基; PTC预应力管桩; 路堤荷载; 土拱效应; 多拱理论; 有限层; 桩-桩帽-土共同作用; 土体反力; 超静孔隙水压力; 负摩阻力; 沉降计算; 沉降预测; 侧向变形; 设计方法
3_V{o[A0【英文关键词】 rigid pile composite foundation ; soft ground; PTC pipe pile; embankment loads; soil arching effect; multi-arch; finite layer method; pile-pile cap-soil interaction; subgrade reaction; excess pore water pressure; negative friction; settlement calculation; settlement prediction; lateral displacement; design method水利论文/v2c6x/cTQ%E9u

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