【作者】 董宏波；

【导师】 朱向荣；

【作者基本信息】 浙江大学 ， 岩土工程， 2004， 硕士

【摘要】 作为一种新的桩基设计理念，沉降控制复合桩基由于具有良好的经济效益和广阔的应用前景，近年来得到了广泛的重视。然而由于认识水平和计算手段所限，许多工程师仍然采用传统的群桩设计方法进行设计，造成了很大的浪费；即使考虑了桩土的共同作用，也往往采用弹性理论将桩与承台或筏板按固定比例分担上部结构荷载，这与沉降控制复合桩基设计理念完全不同。 沉降控制复合桩基工作时部分或全部桩达到一定程度的非线性状态，因此不宜采用弹性理论来计算基础的沉降。PDR法是计算沉降控制复合桩基的一种经验方法，它在一定程度上考虑了桩的非线性和桩—土—筏的共同作用。在PDR法的基础上，依据工程实测资料，本文提出了一种新的计算方法。该法将基础承担上部结构的过程划分为3个阶段，用桩筏相互作用系数对沉降控制复合桩基作非线性分析。另外，计算基础沉降时对土层压缩模量进行修正，能反映当基础下存在超固结土时的影响。 沉降控制复合桩基中各单桩为摩擦桩，桩距较大，因此它的工作性状与单桩比较接近。本文用有限元接触理论分析了单桩在高荷载水平下的非线性特性，计算了桩极限承载力和刺入沉降。在此基础上，建立三维非线性有限元模型，分析筏板刚度、桩刚度、土体弹性模量、桩数对基础平均沉降、不均匀沉降及桩土荷载分担比的影响。 对某工程实例进行了现场试验，测试了基底压力和桩顶反力，并对该工程作了沉降观测。测试结果与三维非线性有限元分析结果显示：基础的平均沉降与常规桩基相比有所增大，但仍然可满足使用要求；采用沉降控制复合桩基并没有降低工程的安全度，而基础造价大大降低，效益显著。更多还原

【Abstract】 As a new philosophy of using piles as settlement controller, Piled raft foundation provides an economical foundation option for circumstances where the performance of shallow foundation doesn’t satisfy the design requirement. As limited cognitive level, civil engineers still use traditional methods to design piled raft foundation. However, some engineers begin to analyse the pile-soil-raft interaction recently. This paper gives some research on the analysis of piled raft foundation subjected to vertical loadings.The character of some piles, maybe all the piles, in piled raft foundation is nonlinear, so elastic theory can not be used to calculate the settlement of piled raft foundation. Poulos-Davis-Randolph (PDR) Method is a empirical calculation method. It is easy to compute the relation between the number of piles and the average settlement of the foundation. A new design method is brought forward based on the PDR methods. The modified PDR Method develops a tri-linear load-settlement curve. The non-linearity of the foundation can be analysed by the factor of the raft-pile interaction. Moreover, a factor behaviors of over consolidated soil is used.The piled raft foundation belongs to large spacing pile foundation. Each pile works similarly as single pile. A complete three-dimensional analysis of a single pile is carried out by finite element analysis. The contact element will be used in order to model the pile-soil interface. The three-dimensional model of piled raft foundation is created. The result of analysis can be used to show the effect of the raft thickness, pile stiffness, Young’s modulus of soils and the number of piles.The modified PDR method is used to design a practical projects. Although the calculated average displacement of the building is less than the actual measurement. It is acceptable.更多还原