典型黄土地区桥梁桩端后压浆钻孔灌注桩受力特性研究

发布时间：2019-04-03 15:25

【摘要】：目前钻孔灌注桩技术在高层建筑和大承载力的基础中已广泛应用，但受桩端软弱土层的影响会大大消弱桩基的的承载力和稳定性，尤其对于黄土区桥梁，由于黄土结构的特殊性，会对桥梁桩基产生一系列的病害。采用桩端后压浆技术能解决桩端软弱层带来的不足，但目前的研究只建立在半经验半理论的基础上，因此确定黄土区桩端后压浆桩基承载力是目前桥梁桩基设计中亟待解决的关键问题。本文结合西安—咸阳机场专用高速段工程桩端后压浆钻孔灌注桩的现场静载试验，以研究后压浆桩基的受力机理为主线，以确定桩基承载性能为目标，在总结国内外研究现状的基础上，采用现场试验、理论分析和数值模拟相结合的技术手段，对典型黄土地区桥梁桩端后压浆桩承载特性进行系统的研究，期望填补桩端后压浆桩在黄土区桥梁桩基受力分析方面的空白，为实际工程需求提供理论及方法支撑，主要研究内容如下： 1.运用Vesic球形扩张原理对桩端后注浆桩基进行分析，对Vesic法中的刚度系数指标进行修正，，克服了原公式不能考虑桩端沉渣、土层空隙等施工过程中带来的影响，得出后压浆桩基在施工过程中，确定土层发生剪切破坏前的水泥浆凝固半径和桩端产生的塑性区范围。 2.基于桩端后压浆的受力机理分析，明确了荷载传递的主要影响因素及承载力计算应考虑的因素，确定了注浆体直径、注浆体高度与桩径之比的控制范围，为黄土地区桥梁桩端后压浆钻孔灌注桩的设计与施工提供了比较合理的技术指标。 3.考虑黄土的湿陷变形受土体模量、湿陷厚度和湿陷系数等不同因素的影响，基于弹性理论，结合桩端后压浆钻孔灌注桩的荷载传递机理分析，提出了典型黄土地区桥梁桩端后压浆的桩基承载力和沉降计算公式，并通过与依托桥梁实测数据的对比分析，验证了理论公式的适用性和可靠性。 4.分别对后压浆和未压浆的试桩进行现场试验，测试在不同荷载下桩身轴力、桩侧和桩端阻力的分布，并对试验数据进行对比分析，探讨了桩端后压浆桩基的荷载传递规律，对采用后压浆技术的钻孔灌注桩的工作机理进行了系统的研究，为典型黄土区桥梁钻孔灌注桩的设计和施工提供了合理的技术指标。 5.结合现场试验，采用非线性有限元分析软件对后注浆桩基的承载性能进行了数值分析，根据模拟计算结果与现场试验结果对比，基于黄土地区桥梁桩端后压浆钻孔灌注桩在设计荷载作用下的荷载沉降机理，对桩端后压浆、桩侧压浆以及桩端与桩侧同时压浆等不同工况对灌注桩承载性能的影响进行了研究，并分析了桩端土变形模量提高后及浆液沿桩侧不同程度的上升机率对桥梁桩基沉降的影响。
[Abstract]:At present, bored cast-in-place pile technology has been widely used in high-rise buildings and the foundation of large bearing capacity, but under the influence of weak soil layer at the end of pile, the bearing capacity and stability of pile foundation will be weakened greatly, especially for bridges in loess area. Because of the particularity of loess structure, a series of diseases will be produced to bridge pile foundation. The technology of post-grouting at pile tip can solve the problem of weak layer at pile end, but the current research is only based on the semi-empirical and semi-theoretical basis. Therefore, determining the bearing capacity of post-grouting pile foundation in loess area is a key problem to be solved in the design of bridge pile foundation. Based on the field static load test of the post-grouting bored pile at the end of the special high-speed section of Xi'an-Xianyang Airport, the main line is to study the stress mechanism of the post-grouting pile foundation and to determine the bearing capacity of the pile foundation. On the basis of summarizing the present research situation at home and abroad, the bearing characteristics of post-grouting pile at the end of bridge pile in typical loess area are systematically studied by means of field test, theoretical analysis and numerical simulation. It is expected to fill the gap of post-grouting pile in the analysis of pile foundation in loess area, and provide theoretical and methodological support for practical engineering demand. The main research contents are as follows: 1. The Vesic spherical expansion principle is used to analyze the post-grouting pile foundation at the end of the pile, and the stiffness coefficient index in the Vesic method is modified. The original formula can not take into account the influence caused by the pile end sediment and the space in the soil layer, etc. It is concluded that during the construction of post-grouting pile foundation, the solidification radius of cement slurry before shear failure of soil layer and the range of plastic zone produced at the end of the pile are determined. 2. Based on the analysis of the stress mechanism of the post grouting at the end of the pile, the main influencing factors of the load transfer and the factors to be considered in the calculation of the bearing capacity are defined, and the control range of the grouting body diameter, the ratio of the grouting body height to the pile diameter is determined. It provides a reasonable technical index for the design and construction of post-grouting bored pile at the end of bridge pile in loess area. 3. Considering that the collapsible deformation of loess is affected by different factors such as soil modulus, collapsible thickness and collapsibility coefficient, based on elastic theory, the load transfer mechanism of post-grouting bored cast-in-place pile at the end of pile is analyzed. The formulas for calculating the bearing capacity and settlement of pile foundation after grouting at the end of bridge pile in typical loess region are put forward, and the applicability and reliability of the theoretical formula are verified by the comparison and analysis with the measured data of the bridge. 4. The field tests of the post-grouting pile and the unpressed pile were carried out to test the distribution of the axial force of the pile body, the resistance of the pile side and the end of the pile under different loads, and the experimental data were compared and analyzed, and the load transfer rule of the post-grouting pile foundation at the end of the pile was discussed. The working mechanism of bored cast-in-place pile with post-grouting technology is systematically studied, which provides a reasonable technical index for the design and construction of bridge bored cast-in-place pile in typical loess area. 5. Combined with the field test, the bearing capacity of post-grouting pile foundation is numerically analyzed by using nonlinear finite element analysis software. According to the simulation results and the field test results, the simulation results are compared with the field test results. Based on the mechanism of load settlement of post-grouting bored pile at the end of bridge pile in loess area under the design load, the post-grouting at the end of the pile is analyzed. The influence of pile side grouting and simultaneous grouting of pile end and pile side on the bearing capacity of cast-in-place pile is studied, and the influence of soil deformation modulus of pile end and the rising probability of slurry along pile side on the settlement of bridge pile foundation is analyzed.
【学位授予单位】：长安大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：U443.15

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