【作者】 张世民；

【导师】 张忠苗；

【作者基本信息】 浙江大学 ， 岩土工程， 2004， 硕士

【摘要】 在沿江、环湖和沿海地区，广泛分布着深厚软土。采用常规桩基础时，不考虑基础底板下地基土的地基承载力，布桩密度往往较大，软土的结构性遭到破坏，同时可能会产生严重的挤土问题，使环境受到影响。为了在确保安全的前提下，尽量发挥桩土体体系的力学性能，做到施工方便，经济合理，可以采用刚柔复合桩基对地基进行处理。 刚柔复合桩基应用的关键是控制基础沉降，本文首先在分析和总结已有各种沉降计算方法的基础上，结合刚柔复合桩基中刚性桩和柔性桩的受力特点，提出了一种刚柔复合桩基沉降计算的新方法—极限应力法：在修正应力法的基础上，假设刚性桩的实际承载力达到其设计承载力极限值，则桩土应力比易于确定，从而可得复合桩基的总沉降量。该方法概念清晰、计算简单，经过工程实例验算表明计算结果与实测值符合良好。另外，在比较了住宅类建筑荷载设计值与建筑物实际发生荷载的差异后，提出了按荷载设计值计算所得沉降应大于沉降实测值30％的观点，可以作为判断沉降计算方法是否偏不安全的一个依据。 其次，采用有限元计算程序，对刚柔复合桩基进行了三维有限元分析，考察了在不同荷载水平下，不同刚柔性桩比例的情况下，复合地基的平均沉降量、土体的沉降等值线和应力等值线以及刚性桩和柔性桩桩顶荷载比值随不同基础荷载水平的变化规律，得出了一些具有实际指导意义的结论：当总桩数不变，长桩比例增加到一定程度时，再增加刚性长桩的数量对地基整体沉降几乎没有什么效果；刚柔桩分布一定，柔性桩实际承载力小于其极限承载力时，外加荷载的增加，刚性单桩和柔性单桩所承当荷载的比值基本不变。 最后，本文对深厚软土地区刚柔复合桩基设计工作中的几个重要内容进行了分析和归纳，不仅总结出复合地基安全系数与柔性桩复合承载力发挥度以及柔性桩复合地基承载力对建筑物总荷载比值的关系，并给出了可供查用的数值计算表，而且还对褥垫层的材料、模量和厚度作了分析，提出推荐采用碎石、毛石片、砂混合垫层加素砼垫层，垫层模量的取值推荐采用20～40MPa，以充分发挥桩和土体的作用，另外，本文还对柔性短桩设计明确提出了在充分发挥材料承载力基础上，按柔性短桩下卧层承载力来确定其长度的原则。更多还原

【Abstract】 Deep and thick soft soil is extensively distributed along the river and wreath lake and etc. When introduced general pile foundation without thinked the toft power under the foundation board, piles needs so many that the structure of soft soil is destroyed and possibly crushed soil problem be caused. For the sake of insuring the safety and as far as possible developing a mechanics function for pile-soil system, we can use rigid-soften composite piles foundation to handle the soft soil.The key to apply rigid-soften composite piles foundation is to control its settlement. Firstly, on the base of analysis and summarize already existing every kind of means to calculate the settlement of the foundation, and combinating stress peculiarity of the rigid pile in rigid-soften composite piles foundation, lodge a new method named utmost stress to calculate the settlement of it. It was proved useful with the practical example. Besides that, bring forward a criterion that the calculation of the settlement must be bigger than the observation of it for 30% to discriminate a method between safe and unsafe.Secondly, by using the great FEM programme, analyzes the mechanism of bearing and deformation of rigid-soften composite piles foundation. Draw a conclusion: exist a specific value, when the number of the rigid pile less than it, increase the number of the rigid pile, effect of reducing the settlement of rigid-soften composite piles foundation is distinct, on the contrary, when the number of the rigid pile more than it, increase the number of the rigid pile, effect of reducing the settlement of rigid-soften composite piles foundation is indistinct.Finally, analyze and sum up some important design’s constitutes of the rigid-soften composite piles foundation. Put an table forward to calculate the safety coefficient. Commend a modus operandi for design of the padding. Besides, confirm a principle of according as the bearing under the end of the soften pile to determine the length of the soften-short pile.更多还原