基于某高层桩筏基础的沉降分析

发布时间：2018-05-26 07:40

本文选题：桩筏基础 + 沉降变形　；参考：《北京建筑大学》2017年硕士论文

【摘要】：随着目前城市化的进程加快,主楼采用高层、裙楼采用低层且附带大型地下车库的建筑物也越来越多。该类建筑的基础类型通常为主楼采用桩筏基础、裙房或车库采用筏形基础。这种类型基础的承载力高、控制变形的能力较好,因而得到了广泛应用,但也存在着众多的问题,如:结构差异沉降较大、基础内力过大等等。而针对这一基础类型的设计工作目前也大多依靠经验计算,无法准确反应地基的变形特征。本文以北京某高层附属裙房及大型地下车库的工程为背景,在现有沉降计算方法以及相关研究的基础上,结合现场沉降监测数据,着重分析土的回弹再压缩变形、上部结构刚度两种因素对该建筑桩筏基础沉降的影响,为相关理论研究与工程设计提供参考。主要研究内容如下:(1)结合现场沉降监测数据,对累计沉降量与单次沉降量进行分析,并由计算结果可知具有深大基础类型的主裙楼式结构的地基沉降过程分为两个阶段:土体回弹再压缩阶段与正常固结阶段;(2)使用PKPM中的5种不同模型对某实际工程的地基基础进行沉降计算,分析了土的回弹再压缩变形、上部结构刚度对沉降计算结果的影响。计算结果表明后浇带荷载系数与土的回弹再压缩是影响裙房沉降计算结果的主要因素;采用文克勒模型时主楼桩筏基础的沉降计算值大于实测值,且计算值约为实测值的2~4倍,采用Mindlin法计算主楼桩筏基础时的沉降结果与实测值较为吻合;(3)在进行较大较深的桩筏基础沉降计算时,PKPM所得计算结果与实测值相差较大的主要原因是:计算模型及理论依据是基于弹性理论而根据经验修正的,计算中忽略了桩土之间的共同作用、不能考虑桩端土的成层性、不能考虑筏板分担荷载的作用,且考虑上部结构刚度的计算理论与方法也不完善;(4)通过使用FLAC3D模拟该工程中桩筏基础的沉降变形,并分析两种因素对该建筑沉降变形的影响。结果发现,土体的回弹对裙房筏板基础沉降的影响明显,而对主楼桩筏基础沉降的影响可以忽略;而上部结构刚度对最终沉降量几乎没有影响,主要是控制桩筏基础的相对变形;(5)结合PKPM、FLAC3D的计算结果并与实测值对比发现,软件计算结果中桩筏基础中部出现最大沉降,并由筏板中部向外部逐渐递减这一特性,主裙楼沉降差异仍与实测值有明显差异;其主要原因是计算时结构荷载被一次性加载至地基土,而实际施工过程中是荷载是逐步施加的;(6)在计算大型复杂的基础沉降时,FLAC3D有着更高的计算精度及准确性,变形特征更加明确,是解决此类工程设计研究问题的重要手段。
[Abstract]:With the acceleration of the urbanization process, the main building adopts the high-rise, the skirt building uses the lower floor and the large underground garage is more and more. The foundation type of this kind of building is usually pile raft foundation for main building, raft foundation for skirt or garage. This type of foundation has high bearing capacity and good ability to control deformation, so it has been widely used, but there are also many problems, such as large differential settlement of structure, excessive internal force of foundation and so on. At present, the design of this kind of foundation is mostly based on empirical calculation, which can not accurately reflect the deformation characteristics of foundation. Based on the engineering of a high-rise apron and a large underground garage in Beijing, based on the existing settlement calculation methods and related research, combined with the site settlement monitoring data, this paper focuses on the analysis of the rebound recompression deformation of soil. The influence of two factors of the superstructure stiffness on the settlement of the pile-raft foundation of the building provides a reference for the relevant theoretical research and engineering design. The main research contents are as follows: (1) combined with site subsidence monitoring data, the accumulative and single settlement amounts are analyzed. The calculation results show that the foundation settlement process of the main skirt building structure with deep and large foundation type can be divided into two stages: soil springback and recompression stage and normal consolidation stage, using five different models in PKPM for a practical construction. The settlement of the foundation is calculated. The influence of the elastic recompression deformation of soil and the stiffness of superstructure on the settlement results is analyzed. The calculation results show that the load coefficient of the post-pouring zone and the rebound recompression of the soil are the main factors affecting the settlement calculation results of the skirt, and the calculated value of the pile raft foundation of the main building is more than the measured value when the Wenkler model is used, and the calculated value is about 2 ~ 4 times of the measured value. The settlement results of pile raft foundation calculated by Mindlin method are in good agreement with the measured values. The main reason for the difference between the calculated results and the measured values is that the calculated results are different from the measured values when calculating the settlement of the pile raft foundation in larger and deeper depth. The main reasons for the difference between the calculated results and the measured values are as follows: And the theoretical basis is based on the elastic theory and is modified by experience, In the calculation, the interaction between pile and soil is neglected, the lamination of pile end soil can not be considered, and the role of raft to share load is not considered. And the theory and method of calculating the stiffness of superstructure is not perfect. The settlement deformation of pile-raft foundation in this project is simulated by using FLAC3D, and the influence of two factors on the settlement deformation of the building is analyzed. The results show that the effect of soil springback on the settlement of the raft foundation is obvious, but the effect on the settlement of the pile raft foundation of the main building can be neglected, while the stiffness of the superstructure has little effect on the final settlement. The relative deformation of pile-raft foundation is controlled and the calculated results of PKPM-FLAC3D are combined with the measured results. It is found that the maximum settlement occurs in the middle of the pile-raft foundation and decreases gradually from the middle of the raft to the outside. The difference between the settlement of the main skirt building and the measured value is still obvious, and the main reason is that the structural load is loaded to the foundation soil at one time during the calculation. In the actual construction process, the load is applied step by step. The FLAC3D has higher accuracy and accuracy in calculating the settlement of large and complicated foundation, and the deformation characteristics are more clear. It is an important means to solve the problem of design and research of this kind of engineering.
【学位授予单位】：北京建筑大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU433

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