【作者】 王涛；

【导师】 刘金砺；

【作者基本信息】 中国建筑科学研究院 ， 岩土工程， 2007， 博士

【摘要】 桩筏基础具有整体性好、竖向承载力高、基础沉降小、调节不均匀沉降能力强、较之桩箱基础具有更加开阔的内部空间的特点，同时可以承受风荷载或地震作用引起的巨大水平力，抗倾覆能力强，目前已成为高重建筑物或软土地基上建筑物常用的基础形式。本文通过野外一系列单桩、平板、带台单桩、带台双桩试验及主楼变刚度调平桩筏及主裙连体基础模型试验，实测出桩-土-桩相互作用影响范围，并针对现场特定土质条件通过回归分析提出对弹性理论相互作用影响系数的修正模型。基于地基、基础、上部结构共同作用原理以及模型试验的沉降与桩顶反力实测结果，论述了桩筏基础传统设计方法存在的弊端，建议采用变刚度调平设计新理念进行优化设计，既最大限度地减小差异沉降，又改善了桩筏基础的受力性状。最后，利用修正后的桩-土-桩相互作用影响系数，采用简化数值计算方法分析桩筏基础上部结构-基础-地基(桩土)的共同作用。主要完成以下工作：1．通过大比例尺模型试验及现场实测的结果与弹性理论解的对比，指出弹性理论解夸大了桩-桩、桩-土、土-土相互作用影响，造成沉降计算值偏大和过高估计桩顶反力的不均匀性(或筏底地基土反力的不均匀性)，并针对现场特定土质条件通过回归分析，提出对弹性理论相互作用影响系数的修正模型。2．对承台分担荷载比例的研究现状进行了总结，通过对带台单桩、群桩模型承载性状的分析，说明带台单桩的承载性状与群桩的承载性状并不完全相同。因此，不能将带台单桩的试验结果简单地推广到群桩的设计计算中去。在带台单桩试验中，发现带台单桩的极限承载力大于或等于单桩与平板极限承载力之和，即“1+1≧2”的结论，而在复合群桩试验中，复合桩基的极限承载力在桩距较小时则远小于各单桩与平板极限承载力之和，而且即便在较大桩距情况下，承台效应系数也难以发挥到1.0。现场大型群桩模型试验结果与弹性理论关于承台分担荷载的计算结果比较后表明，实测的承台分担荷载比也远远小于弹性理论计算结果。3．运用变刚度调平的概念设计理念，通过改变主楼下地基和基桩的刚度分布，使之与荷载匹配，从而促使框筒结构高层建筑主楼的变形趋向均匀，基础的冲、剪、弯内力、上部结构次生应力减小。这种变刚度调平的概念设计思想通过现场模型试验进行了验证，并介绍了应用此法进行某工程优化设计的过程。4．本次模型试验主裙之间未考虑变刚度调平和设置沉降后浇带，也未采取相应增沉措施，目的在于研究主裙连体对于沉降、荷载传递、筏板和上部结构内力等的影响，从而导致试验结果中主裙连体基础筏板纵向相对差异沉降略大于规范允许值。笔者为此对减小主裙差异沉降问题进行讨论，主裙连体设计应使基础沉降协调，高层主体采用桩筏基础使其沉降减至最小；裙房可采用天然地基上的独立基础、格形基础。地下水位高时，格形梁之间设抗水板，也可采用在梁板式筏基的中间板下敷设苯板、炉渣等增沉作法。基于基坑开挖回弹再压缩减小差异沉降的有利效应，当裙房超过4～5层或当裙房采用上述增沉措施时可不设沉降后浇带。模型试验无法模拟基坑开挖引起的回弹再压缩效应，这也是导致主裙间差异沉降略大于规范允许值的原因之一。5．利用修正后的桩-土-桩相互作用影响系数，对上部结构采用子结构法进行刚度凝聚、基础筏板采用中厚板理论、桩土应用Mindlin有限压缩层混合修正模型对桩筏基础进行简化计算。计算结果与模型试验结果吻合较好。更多还原

【Abstract】 Pile raft foundation has the good integrity, the high vertical bearing capacity, the small foundation settlement, strong ability to adjustment uneven subsidence, and more open internal spatial compared with the pile box foundation. Simultaneously it may rely on greatly level load caused by the wind load or the earthquake function and has strong ability to anti- overturn. At present pile raft foundation applied in the high heavy building or the building of soft soil area has become commonly used foundation form. Pile-soil-pile interaction influence scope is measured and the revision models on pile-soil-pile interaction influence coefficient of the theory of elasticity are obtained by a series of regression analysis, which is based on a series single pile, plate, single pile with cap, double piles with cap experiments and the monolithic pile raft foundation of principal building and podium model experiment of principal building adjusted foundation rigidity design for reducing different settlement in site. The malpractice of pile raft foundation tradition design method is elaborated, which is based on interaction principal of superstructure-foundation-subsoil and test results of subsidence and pressure of on the top of pile. The new idea of adjusted foundation rigidity design for reducing different settlement is suggested to both reduce the unequal settlement, and improvement pile raft foundation stress character. Finally, superstructure, foundation and subsoil (pile-soil) interaction is analyzed by simplification numerical analysis method based on revised pile-soil-pile interaction influence coefficient. The main works as follows:1. This paper pointed out that the theory solution of elasticity exaggerated the pile - pile, pile - soil, soil - soil interaction influence through the contrast between the result of large scale model tests, the test results in-situ and the theory of elasticity solution, which lead to the large subsidence predicted value and overestimate the head of pile reaction the non-uniformity (or raft bottom foundation earth pressure non-uniformity). Finally, the author pointed out that the difference between the theory solution of elasticity and the real value must be estimated at most, and the theory solution of elasticity must be revised through lots of the test results in-situ and model tests results. 2.This paper summarize the research actuality on the load proportion shared by cap and analyze single pile with cap and group pile foundation bearing capacity behavior in order to explain that there are differences between the bearing capacity behavior of single pile with cap and group pile foundation. Therefore, we cannot bring single pile with cap’s bearing capacity test result simply into group pile foundation design calculation. The ultimate bearing capacity of single pile with cap is much larger than the sum of the ultimate bearing capacity of single pile and plate under the condition of small pile spacing. Under the condition of large pile spacing pile cap effect coefficient can’t also reach to 1.0. The conclusion "1+1≧2" is obtained. But in composite group piles tests, foundation soil beneath the pile cap bearing capacity then greatly reduces. The conclusion that ultimate bearing capacity of composite pile foundation is smaller than the sum of ultimate bearing capacity of all single piles and plates is obtained. Finally, the conclusion that the load proportion shared by cap in-situ is much smaller than the proportion calculated by elasticity theory is obtained by contrast between group piles model tests results and elasticity theory calculation on the load proportion shared by cap.3.In this thesis the applied concept optimized design idea based on adjusted foundation rigidity of principal building, that is through changing the rigidity distribution of subsoil and foundation piles to mate with the load distribution, which results in minimizing differential settlement and interior force of foundation of high-rise buildings with frame-tube or frame-shear wall structures and tower-podium connected buildings. The concept design based on adjusted foundation rigidity has been verified through the large scale model tests in site. The editor introduced the optimization design process applying the idea in the end.4.Adjusted foundation rigidity design for reducing different settlement, post-pouring belt, measure of increasing settlement are not adopted in order to research change of settlement, load transferring, internal force of raft board and super-structure under the condition of the monolithic pile raft foundation of principal building and podium, which lead to relative unequal settlement to be bigger than the permissible value of standard slightly directly. The author specially carry on the discussion in order to reduce principal building and podium unequal settlement, which point out that principal building and podium foundation connecting design may consider to coordinate the two foundation settlement method, namely taking the pile raft foundation to reduce the high-level part subsidence. The independent foundation and standard shape foundation in the natural foundation may be used in the podium. When the ground water level is high, the anti-water board must be used between the cellular girder. In order to increase settlement the slag and benzene board may be layed under the beam-board raft foundation. Swelling and recompression based on structure excavation may cause the advantageous effect to reduce the unequal settlement. When the podium surpasses 4～5 layer the subsidence pouring belt may be not established under the condition of adopting increasing settlement measures. The model experiment is unable to simulate subsoil soil swelling and recompression effect that is caused by structure excavation, which also causes the unequal settlement slightly to be bigger than standard permissible value between the mail building and podium.5.Sub-structure law is applied to carry on the rigidity to condense of superstructure. At the same time medium thickness board theory and Mindlin-limited compression layer mixed revision model is adopted to simply calculate interaction of pile raft foundation. The uniformity of numerical analysis results and the model test results is good.更多还原