【作者】 张四化；

【导师】 郭院成；

【作者基本信息】 郑州大学 ， 结构工程， 2014， 博士

【摘要】 桩与土的空间作用效应，使相同基础沉降下小承台板长短桩复合地基的承载性状与大承台板长短桩复合地基的承载性状之间存在差异。这种差异使得，目前用长短4桩复合地基静载荷试验结果验证长短桩复合地基承载力和沉降计算理论存在一定问题。而现实中，受场地和加载条件限制，多数情况下又仅能进行长短4桩复合地基静载荷试验。为解决理论与现实之间的矛盾，需要研究桩土空间作用效应问题。本文在CFG桩-PHC管桩长短4桩复合地基静载荷试验研究的基础上，首先，通过数值模拟方法，探讨桩土间的空间作用效应问题，挖掘其与刚性基础下刚性长短桩复合地基承载性状的相关性。分析了刚性基础下刚性长短桩复合地基中荷载-沉降、桩-土应力、桩端阻比及桩刺入变形随桩数变化的规律，并给出了拟合函数表达式。研究表明：在相同荷载水平下，桩数越多，承台板沉降越大；随着荷载水平增加，同等荷载水平下，各模型承台板沉降差逐渐增大；相同承台板沉降下，桩数越多，长短桩复合地基所承担的荷载水平越小；随着承台板尺寸（桩数）增加，地面和深层土体水平位移量和应力扩散范围逐渐增大，最大水平位移逐渐向土层深部传递，长桩、短桩桩顶和桩端应力逐渐减小；随着承台板沉降增大，承台板等沉下不同模型中长桩或短桩桩顶和桩端应力差异逐渐减小，桩顶平面和长桩桩端平面土应力逐渐减小，短桩桩端平面土应力逐渐增加，长桩端阻比逐渐增大，中心短桩和长桩上刺入变形逐渐减小，角桩长桩上刺入变形逐渐增加，下刺入变形逐渐减小。其次，诠释了桩长、桩间距及褥垫层厚度变化对刚性基础下刚性长短桩复合地基中荷载-沉降、桩-土应力、桩端阻比及桩刺入变形随桩数变化的规律的影响，并评判了影响度及其变化规律。研究表明：相同承台板沉降下，桩长变化对长短桩复合地基中短桩桩端平面土应力、桩顶应力、桩上下刺入变形随桩数变化的规律的影响显著；而对长短桩复合地基中荷载-沉降、桩端应力随桩数变化规律的影响在现场试验或工程设计时可以不予考虑；相同承台板沉降下，桩间距变化对长短桩复合地基承载力的影响，随着荷载增加逐渐增大，对长短桩复合地基中桩顶土应力、短桩端阻比随桩数变化的规律影响显著，且随着桩数增加，其影响程度逐渐减小，对桩刺入变形、桩顶和桩端应力、桩端阻比随桩数变化规律的影响在现场试验或工程设计时可以不予考虑；相同承台板沉降下，褥垫层厚度变化对长短桩复合地基中桩顶和桩端应力随桩数变化的规律影响显著，且随着桩数增加，其影响程度逐渐减小，而对于荷载-沉降、桩顶和桩端平面土应力、桩端阻比、桩顶和桩端刺入变形随桩数变化规律的影响在现场试验或工程设计时可以不予考虑。最终，基于Boussinesq和Mindlin解，提出了长桩下刺入变形和下卧层附加应力计算方法；以长桩控沉为沉降计算理念，同时考虑桩土空间作用效应、长桩上下刺入变形、长桩桩顶褥垫层压缩变形及桩端下卧层压缩变形，提出了刚性基础下刚性长短桩复合地基沉降计算理论方法；通过工程实例计算与分析，验证了该计算方法的合理性与可行性。更多还原

【Abstract】 Under the same settlement, there is a difference in bearing capacity betweensmall raft long-short pile composite foundation and large raft long-short pilecomposite foundation because of the pile-soil spatial effect. This difference makessome problems in theory when using the results of composite foundation (4piles)that under the test of static load to verify the long-short pile composite foundationbearing capacity and settlement. Haveover, for most of the actual project, only thestatic load test of four piles composite foundation or single pile compositefoundation is done limited by the space and loading conditions. In order to solve thecontradiction between theory and reality, the pile-soil spatial effect need to bestudied.This paper based on CFG pile and PHC pipe long-short pile (4piles) compositefoundation under the test of static load. Firstly, through the method of numericalsimulation to discuss the problem of the pile-soil spatial effect, the correlationbetween the pile-soil spatial effect and the capacity of the rigid long-short pilecomposite foundation is studied. This paper has analyzed the changing rule ofload-settlement, pile-soil stress, pile end resistance ratio, pile penetrationdeformation, with different number of piles in rigid long-short pile compositefoundation, and has given the trinomial fitting function. Results have shown that,under the same load level, the more the numbers of piles, the settlement of bearingcounter is larger.With the increase of load value, the differential settlement isgradually increasing under the condition of the same load. The bearing capability oflong-short pile composite foundation is smaller with the amount of piles is largerunder the condition of same settlement. When the size of board becomes bigger orthe amount of piles is bigger, horizontal displacement in the superficial and deep soiland diffusion scope of stress are increasing; the maximal horizontal displacement ispassing to the depth of soil; the stress of top and bottom of long and short piles isdecreasing. The difference of stress among the different models under the conditionof the same settlement with settlement is increasing. For long piles, the stress of thetips is gradually decreasing, in contrast, the short piles is increasing. The ratio of tip resistance is increasing and the upper penetration deformation of long and short pilesin the central place is smaller, while in the corner place the upper penetratedeformation is bigger and the download penetration deformation is smaller for thelong piles.Then, the rule is explained that effect of the length, space of piles and thicknessof bedding cushion on load-settlement, pile-soil stress, ratio of tip resistance andupper penetration deformation, and the influence degree and change rule areevaluated. The research indicates that the effect of pile length on the end and topstress of short piles and upper and download penetration deformation is obvious. Butthe rules of effect of load-settlement and tip stress of piles on the amount of pilescan be ignored. Unde the condition of same settlement, the effect of the change ofpile space on capacity is increasing with the load is increasing. The effect of theamount of piles on soil stress of pile top and ratio tip resistance is obvious and theinfluence is gradually smaller with the amount is bigger, while the effect on thedownload penetration deformation, top and bottom stress of piles and tip resistancewill be ignored. The effect of the thickness of bedding cushion on stress of pile topand bottom is obvious under the same settlement, and the influence is graduallysmaller with the amount is larger. While the factors including load-settlement, soilstress of top and bottom of piles, ratio of stress top to stress bottom, penetrationdeformation of top and bottom piles can be ignored.Lastly, the calculation method about downward penetration deformation of longpiles and underlying stratum additional stress is proposed through combining theBoussinesq and Mindlin. The theory about settlement calculation of rigid long-shortpile under rigid foundation is suggested which is based on the idea of controllingsettlement of long piles and is taking into account spatial effect of pile and soil,upper and downward penetration deformation, compression deformation of cushionin the top of long piles and compression deformation of under soil in the tip of longpiles.更多还原