多年冻土地基群桩基础承载性状数值模拟研究

发布时间：2018-03-05 15:08

本文选题：多年冻土　切入点：群桩　出处：《兰州交通大学》2017年硕士论文　论文类型：学位论文

【摘要】：多年冻土在我国的东北以及青藏高原等地区分布广泛,多年冻土地区建筑物基础的长期承载性状是保证寒区建筑施工与运营安全的基石,而我国的多年冻土性质复杂,冻土地基中基础的承载力受冻土温度、地质条件、冻土类型以及基础形式等各种因素的影响。桩基础有着承载力大适用性广,施工简便,对地温的扰动较小等优点,冻土区的建筑物基础多采用桩基础。但是由于冻土性质的复杂,分区的多样化,对多年冻土地区桩基础特别是群桩基础的研究没有普通土那样完善。而且由于冻土区群桩基础无法进行现场载荷试验,而室内模型试验又很难模拟冻土中群桩复杂的工作状态,因此进行数值模拟分析是十分有意义的。本文先回顾了一些以往对寒区工程桩基础的研究,对受竖向荷载下群桩基础的基本工作机理进行了阐述。详细的介绍了大型有限元分析软件Midas/GTS,并介绍了数值模拟的有限元模型,计算单元、接触单元以及本构模型的选取。采用此软件进行三维可视化建模,通过对青藏高原昆仑山垭口的一例单桩承载试验进行了建模分析,数值模拟分析得到的结论与现场试验实测值满足工程误差需要,验证了数值模拟分析参数选取的准确性以及此有限元软件对冻土桩基分析的可行性,然后建立了多种工况下单桩和群桩的数值模型,分析了不同工况对多年冻土区单桩以及群桩基础的承载性状的影响。本文选取了三种不同冻土温度的的土参数,分别建立了10m桩长三种不同桩径的单桩模型以及15m桩长1m桩径的四种不同桩距的2×2群桩和梅花桩群桩三维模型,对冻土温度和桩径对单桩承载特性的影响以及桩数、桩间距对群桩基础的影响进行了研究,主要分析了桩基础受竖直方向荷载下的沉降、轴力、桩端阻力以及桩侧冻结力的变化,探讨了群桩的群桩效应、破坏特征、破坏方式以及桩侧冻结力的发挥过程。从中总结出多年冻土地基桩基础增大桩径以及降低冻土温度可以显著提高承载力并且减少沉降;一定范围内群桩桩距的增大可以减少沉降,有限的提高群桩承载力;在不改变桩距的情况下增加桩数对冻土中桩基承载力提高不明显以及会增大沉降等结论。并且证明了有限元Midas/GTS对冻土中桩基受力模拟的可行性。
[Abstract]:Permafrost is widely distributed in Northeast China and Qinghai-Tibet Plateau. The long-term bearing behavior of building foundation in permafrost region is the cornerstone to ensure the construction and operation safety in cold region, but the permafrost is complex in nature in our country. The bearing capacity of foundation in permafrost foundation is affected by various factors, such as temperature of frozen soil, geological condition, type of frozen soil and form of foundation, etc. Pile foundation has many advantages such as wide applicability of bearing capacity, simple construction, small disturbance to ground temperature, etc. The foundation of buildings in permafrost regions mostly adopts pile foundation. However, due to the complexity of frozen soil properties, the diversity of the zoning, The research on pile foundation in permafrost region, especially pile group foundation, is not as perfect as ordinary soil, and because pile group foundation in permafrost region can not carry out field load test, it is difficult to simulate the complex working state of pile group in frozen soil by indoor model test. Therefore, it is very meaningful to carry out numerical simulation and analysis. In this paper, some previous researches on engineering pile foundation in cold region are reviewed. The basic working mechanism of pile group foundation under vertical load is expounded, the large finite element analysis software Midas / GTS is introduced in detail, and the finite element model and calculation element of numerical simulation are introduced. The selection of contact element and constitutive model. By using this software, a single pile bearing test in Kunlun Mountain pass of Qinghai-Xizang Plateau is modeled and analyzed. The conclusion of numerical simulation analysis and the measured value of field test meet the need of engineering error. The accuracy of parameter selection of numerical simulation analysis and the feasibility of this finite element software for the analysis of frozen soil pile foundation are verified. Then, the numerical models of order pile and pile group under various working conditions are established, and the influence of different working conditions on the bearing behavior of single pile and pile group foundation in permafrost region is analyzed. The soil parameters of three kinds of frozen soil temperature are selected in this paper. Three kinds of single pile models of 10m pile length and three different pile diameters are established, and four kinds of 3D models of 2 脳 2 pile group and plum blossom pile group with different spacing of 15m pile length 1m pile diameter are established respectively. The effects of frozen soil temperature and diameter on the bearing characteristics of single pile and the number of piles are also discussed. The influence of pile spacing on pile group foundation is studied. The variation of settlement, axial force, pile tip resistance and pile side freezing force under vertical load of pile foundation are analyzed, and the pile group effect and failure characteristics of pile group are discussed. It is concluded that increasing pile diameter and decreasing frozen soil temperature can significantly increase bearing capacity and reduce settlement of pile foundation on permafrost foundation. The increase of pile spacing in a certain range can reduce the settlement and improve the bearing capacity of pile group. Without changing the pile spacing, the increase of pile number is not obvious to the bearing capacity of pile foundation in frozen soil and will increase the settlement, etc. The feasibility of finite element Midas/GTS to simulate the force of pile foundation in frozen soil is proved.
【学位授予单位】：兰州交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU473.1

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