【作者】 蒋建忠；

【导师】 温晓贵； 杨晓军；

【作者基本信息】 浙江大学 ， 岩土工程， 2006， 硕士

【摘要】 桩筏基础是高层建筑广泛采用的一种重要的基础型式，关于桩筏基础与地基共同作用的研究受到学术界和工程界的普遍关注。虽然人们对该课题已进行了大量分析与探讨，研究成果显著，但由于其涉及因素很多，十分复杂，目前许多问题尚未圆满解决。计算机的飞速发展，使得人们在进行试验研究的同时，有可能通过理论分析来进一步认识、发现桩筏基础与地基共同作用的机制，研究探讨有效、实用的分析方法，以达到为工程服务的目的。随着我国经济建设的发展，沿海地区高层建筑的建设正处于高速发展时期。沿海地区常为软弱地基，常需要对成百上千根桩进行沉降分析。传统有限元法和边界元法都需要对桩进行单元划分，需要建立很大的桩土刚度矩阵，因此不适用于大规模桩筏基础的分析。本课题主要任务是研究适合于大规模桩筏基础非线性简化分析方法。 本课题主要进行以下工作：首先对现有的各种单桩沉降的计算方法进行综述，讨论了各方法的优缺点及其适用范围；提出考虑桩土相互作用非线性的单桩分析方法，为后文的群桩沉降分析作理论上的铺垫。其次，使用相互作用系数的方法分析群桩系统的沉降可以大大减少计算时间。由于Poulos提出的相互作用系数的方法没有考虑桩的“加筋”和“遮帘”作用，因此群桩的计算沉降通常比实测值要大。本文提出考虑了桩的“加筋”影响的相互作用系数的简化计算方法，并通过修正桩—桩之间地基的剪切模量来考虑桩的“遮帘”的影响。经过实例分析比较，证明该计算方法可以给出更符合实际情况的相互作用系数。最后，本课题提出一种分析大规模桩筏基础非线性变形的简化分析方法。研究了群桩沉降的主要计算参数—桩周土的弹性模量和泊松比的确定方法，提出一种通过单桩现场实测荷载位移曲线，使用遗传算法反分析土的材料参数的实用方法。同时在桩筏基础沉降分析中，充分利用单桩载荷试验曲线，将它用于桩筏基础的非线性分析中，从而使得沉降预测结果更符合工程实际情况。本文将筏板假定为弹性薄板。筏板下的群桩假定为相互作用的非线性弹簧，使用双曲线函数拟合载荷试验的Q-S曲线，并用它来模拟桩在荷载下的非线性响应。采用相互作用系数法分析桩—桩间的相互作用，同时考虑桩的“加筋”对相互作用系数的影响。为了简化计算，采用多项式拟合桩—桩和桩—土相互作用系数。使用弹性半空间或有限层理论分析土节点间的相互作用。经过实例分析比较，该方法不但可以节省大量机时，而且可以得到较满意的预测结果。 通过上述研究，本课题成功解决了大规模桩筏基础非线性沉降分析问题，使得对大规模桩筏基础沉降分析变得十分方便。同时，将试桩载荷试验结果运用于群桩沉降分析中，使得桩筏基础的沉降结果更符合实际工程情况。因此，本文的研究具有极大的理论和实用价值，有着十分广阔的工程应用前景。更多还原

【Abstract】 Piled raft foundations, which is extensively used, is an important foundation pattern of high rise buildings. The researches on the interaction characteristics of piled raft foundations and the soil have been being paid close attention to by academic and engineering circles. Though a lot of achievements in the field have been obtained in recent thirty years, many problems remain unsolved for their complex nature. With the rapid development of computer, it is possible to realize further the interaction mechanism by theoretical analysis and to try to find out reasonable, practical and effective analytical methods of piled raft foundations. Along with the high speed developing of country economic, more and more skyscrapers are built in coastal area. Hundreds and thousands piles are necessary to support bigger and bigger structural loads. Traditional the finite element methods and the boundary element methods need to divide piles into a great number of elements, which can cause the enormous pile-soil stiffness arrays. So the piled raft foundations which have many piles can not be analyzed by these methods in a little time. The paper focus on the simple method for analyzing nonlinear interaction of large scale piled raftsThe main work of this paper includes: first, attention is confined to the displacement behavior and computation methods of single piles, the approach is presented for the analysis of non-linear responses of vertically loaded single pile; second, pile group settlement analysis by pile-pile interaction factors can save a lot of computing time. However, the traditional interaction factors method that Polous developed can’t consider "reinforcing effect" and "shadowing effect" of pile groups. Thus, pile group computed settlement is more than measured settlement. This paper give an simplified approach which considers "reinforcing effect". Moreover , "shadowing effect" of pile groups can be considered by modifying the soil shear modulus between two piles. Comparisons show that the simplified approach can give more reasonable interaction factors with those from measured results; Finally ,the paper puts forward a simple method for analyzing the nonlinear interaction of large piled rafts. This paper describes the method to estimate parameters including soil modulus and Poisson’s ratio, and develops a technique of back-analyze soil modulus from appropriate interpretation of field pile load tests. The simple method applies the single pile load test’s results to the settlement of piled rafts .The raft is modeled as a thin plate and the piles are modeled as the interacting nonlinear springs. The single pile load test’s Q-S curves can be matched by the hyperbola function. The non-linear characteristic of the piles can be modeled by the hyperbola function. The interaction between piles is analyzed by interaction factors, "restraint" action between piles is considered in this paper, the interaction factors between pile-pile and pile-soil are matched by the multinomial regression. The interaction between soil elements can be analyzed by elastic semi-space or finite layer theory. Compared with the results of the full piled raft analysis and the model pile groups, the approximate method can not only save a large amount of computing time but give the reasonable results.With the listed above analysis, the paper successfully solve the problem that the nonlinear settlement of large scale piled rafts can not be analyzed appropriately. Moreover, the simple method applies the single pile load test’s results to the settlement of piled rafts, which can achieve more appropriate results. It should be useful for projects.更多还原