循环荷载作用下加筋碎石垫层—夯实水泥土楔形桩复合地基工作性状研究

发布时间：2019-01-05 03:27

【摘要】：加筋碎石垫层-夯实水泥土楔形桩复合地基技术,是近年来被提出来的一种新型软土地基加固方法。为揭示该新技术在循环荷载下的工作特性,本文采用模型试验与三维数值分析(FLAC3D软件)相结合的方法,从夯实水泥土桩土接触界面摩擦特性、土工格栅加筋碎石垫层工作特性、地基土的动力特性、复合地基在循环荷载作用下的承载特性,以及复合地基应力场和位移场等5个方面,对循环荷载作用下加筋碎石垫层-夯实水泥土楔形桩复合地基的工作特性展开了系统的研究,得出了以下结论:1、夯实水泥土-土接触面的摩阻力随养护龄期的增长、土的含水量减少、水泥土水泥掺量增加而增大,并存在一个合理的水泥掺量。2、褥垫层能够通过调节荷载分布,来减小基础沉降。垫层并不是越厚越好,而是存在一个合理的垫层厚度;在垫层中加入土工格栅后,可以进一步减小基础沉降;在垫层厚度允许的情况下,土工格栅层数越多基础沉降越小。3、阻尼比?随着动应变的增大呈先增大后减小的趋势,并在最后保持稳定;随着动应变的增加以用围压的降低,土的动弹性模量越来越小,同时在动应变较小时,围压对土的动弹性模量的影响较显著;动强度随着振动次数增加而减小,且在振次较小时,动强度下降速度较快,随着振动次数的增大,动强度下降趋缓。4、在循环荷载作用下,循环荷载峰值、循环次数、有无格栅以及楔角大小等因素对复合地基沉降、桩-土应力比、桩身应变有较大影响;楔形桩的特殊形状,可以增强桩-土相互作用,减小复合地基沉降,增大桩-土应力比,减小桩顶应力与桩顶的应力集中,优化桩身应力分布,从而提高复合地基的承载力;当夯实水泥土楔形桩与碎石垫层形成双向增强体复合地基时,在垫层中加入土工格栅可以进一步提高复合地基的承载力。5、运用FLAC3D建立的复合地基模型模拟的结果与试验结果有较好的吻合性;通过对复合地基和桩体的应力场和位移场进行分析,进一步研究了加筋碎石垫层-夯实水泥土楔形桩复合地基在循环荷载作用下的应力分布特性和沉降变化规律,并进一步证实了夯实水泥土楔形桩的承载特性优越于等截面桩。
[Abstract]:Reinforced gravel cushion-rammed cement-soil wedge pile composite foundation technology is a new kind of soft soil foundation reinforcement method proposed in recent years. In order to reveal the working characteristics of the new technology under cyclic load, this paper adopts the method of model test and three-dimensional numerical analysis (FLAC3D) to study the friction characteristics of compacted cement-soil pile / soil contact interface. The working characteristics of geogrid reinforced gravel cushion, the dynamic characteristics of foundation soil, the bearing characteristics of composite foundation under cyclic load, and the stress field and displacement field of composite foundation are discussed. The working characteristics of reinforced gravel cushion and compacted cement-soil wedge pile composite foundation under cyclic loading are studied systematically. The following conclusions are obtained: 1. The friction of compacted cement-soil-soil interface increases with the curing age. The soil water content decreases and the cement content increases, and there is a reasonable cement content. 2. The cushion can reduce the foundation settlement by adjusting the load distribution. The cushion is not the thicker the better, but there is a reasonable cushion thickness, after the addition of geogrid in the cushion, the foundation settlement can be further reduced. When the thickness of the cushion is allowed, the more the number of geogrid layers, the smaller the foundation settlement. 3, damping ratio? With the increase of dynamic strain, the dynamic strain increases first and then decreases, and keeps stable at last. With the increase of dynamic strain and the decrease of confining pressure, the dynamic elastic modulus of soil becomes smaller and smaller, and when the dynamic strain is small, the influence of confining pressure on the dynamic elastic modulus of soil is more obvious. The dynamic strength decreases with the increase of vibration times, and decreases more quickly with the increase of vibration frequency, and with the increase of vibration times, the dynamic strength decreases slowly. 4. Under cyclic load, the peak value of cyclic load and the number of cycles decrease. The influence of grille and wedge angle on settlement of composite foundation, pile-soil stress ratio and strain of pile body is significant. The special shape of wedge pile can enhance the pile-soil interaction, reduce the settlement of composite foundation, increase the pile-soil stress ratio, decrease the stress concentration of pile top and pile top, optimize the stress distribution of pile body, and improve the bearing capacity of composite foundation. When compacted cement-soil wedge pile and gravel cushion form bidirectional reinforcement composite foundation, the bearing capacity of composite foundation can be further improved by adding geogrid to the cushion. The simulation results of the composite foundation model established by FLAC3D are in good agreement with the test results. Through the analysis of the stress field and displacement field of composite foundation and pile, the stress distribution characteristics and settlement variation of reinforced gravel cushion and rammed cement-soil wedge pile composite foundation under cyclic load are further studied. It is further proved that the bearing capacity of tamped cement-soil wedge pile is superior to that of equal section pile.
【学位授予单位】：湖南工业大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU447;U416.16

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