刚性基础下刚性长短桩复合地基桩土空间作用效应研究

发布时间：2018-07-14 18:01

【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。
[Abstract]:The spatial action effect of pile and soil makes the bearing characters of the small bearing plate long short pile composite foundation differ from the bearing characters of the long short pile composite foundation with the large bearing platform. This difference makes the calculation of the bearing capacity and settlement of the long short pile composite foundation by the static load test results of the long short 4 pile composite foundation. In fact, in reality, under the limitation of site and loading condition, the static load test of 4 pile composite foundation can only be carried out in most cases. In order to solve the contradiction between theory and reality, it is necessary to study the effect of the spatial effect of pile and soil.
In this paper, based on the static load test of CFG pile -PHC pipe pile 4 pile composite foundation, first, through the numerical simulation method, the spatial effect effect between pile and soil is discussed, and the correlation between the bearing behavior of rigid long short pile composite foundation under rigid foundation is excavated and the load sedimentation in rigid long short pile composite foundation is analyzed. Down, pile soil stress, pile end resistance and pile thrust deformation change with the number of piles, and give a fitting function expression. The study shows that under the same load level, the more the pile number, the greater the settlement of the platform plate; with the increase of load level, the settlement difference of the model bearing plate increases gradually under the same load level; the same bearing platform settlement, The more the pile number, the lower the load level of the long and short pile composite foundation. With the increase of the plate size (pile number), the horizontal displacement and the stress diffusion range of the ground and deep soil gradually increase, the maximum horizontal displacement gradually passes to the depth of the soil layer, and the stress of the long pile, the short pile top and the pile end gradually decreases; with the increase of the settlement of the platform plate, the bearing capacity is increased. The stress difference between the top and the pile ends of the long pile or the short pile gradually decreases, the stress of the pile top plane and the long pile end decreases gradually, the stress in the end plane of the short pile increases gradually, the end resistance ratio of the long pile increases gradually, the piercing deformation of the short pile and the long pile gradually decreases, and the spiny deformation on the long pile pile increases gradually. The deformation of the lower stab gradually decreases.
Secondly, the influence of pile length, pile spacing and cushion thickness on load settlement, pile soil stress, pile end resistance ratio and pile number change with pile number in rigid foundation pile composite foundation under rigid foundation is explained, and the influence degree and change law are judged. The stress of the short pile at the end of the pile composite foundation, the stress of the pile top, the deformation of the pile on the pile and the pile number change with the number of piles, and the effect of the load settlement on the pile and the change law of the pile number in the pile composite foundation can not be considered in the field test or the engineering design; the pile spacing is changed under the same settlement plate settlement. The influence on the bearing capacity of the long and short pile composite foundation increases with the increase of load. The influence of the pile top soil stress and the short pile end resistance ratio with the number of piles in the long and short pile composite foundation is significant, and with the increase of pile number, the influence degree gradually decreases, the deformation of pile, the stress of the pile top and the pile end and the pile end resistance ratio change with the number of piles. The influence on field test or engineering design can not be considered. Under the same slab settlement, the change of cushion thickness on pile top and pile end stress changes with the number of piles in the composite foundation of long and short pile, and with the increase of pile number, the influence degree gradually decreases, and the stress on the load settlement, pile top and pile end plane soil stress, pile The influence of the end resistance ratio on the deformation of pile top and pile tip with the variation of pile number can not be considered in field test or engineering design.
Finally, based on the Boussinesq and Mindlin solutions, the calculation method for the additional stress of the long pile under the spiny deformation and the lower lying layer is proposed, and the long pile controlled settlement is considered as the settlement calculation, and the space action effect of the pile and soil, the deformation of the long pile up and down, the compression deformation of the bedding cushion and the compression deformation of the lower lying layer are put forward, and the rigidity under the rigid foundation is put forward. The theoretical method of settlement calculation for long short pile composite foundation is verified and verified by engineering examples.
【学位授予单位】：郑州大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TU473.1

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