一种新型试桩方法及其荷载传递机理与桩承载力转换研究

In the field of civil engineering, more and more large diameter piles and super-long piles appear. By the current means of pile test, it is difficult to satisfy the requirement of testing the bearing capacity of this kind of pile.. This project proposes a new test pile called self-anchored test pile , it’s major scientific issues to study the stress distribution of the soil around the pile between the self-anchored test pile and the traditional test pile as well as the difference of the law of load transfer between them. Use the methods of theoretical analysis, mathematical modeling, indoor model test and in-situ full-scale test to research the load transfer law of self-anchored test pile and traditional test pile, and analysis the different characteristics of stress distribution in soil and the transfer characteristics of pile bearing capacity.Main research contents and innovation points:（1）Research the stress distribution law of soil caused by different loading modes , and establish the load transfer function of self-anchored test pile body and pile tip, considering the interaction between pile and soil.（2）Establish the influence model of pile end bearing capacity caused by different loading modes on pile side friction.（3）Revealing load transfer mechanism of self-anchored test pile, establish the conversion calculation model of the bearing capacity of self-anchored test piles.（4）Based on numerical simulation and similarity simulation, establish the theoretical method for determining the position of equilibrium point.. The results of this project reveal the mechanical and deformation characteristics of self-anchored test pile, enrich and develop the theory of pile foundation testing, and provide theoretical support for the popularization and application of self-anchored test pile.

在土木建筑领域，随着大直径桩、超长桩越来越多，目前的试桩手段已经难以满足这类桩承载力的测试需求。. 本课题提出一种新的试桩方法-自锚试桩法，以自锚试桩与传统试桩的桩周围土应力分布、荷载传递规律的差异性作为主要科学问题，采用理论分析、数学建模、室内模型试验与原位足尺试验相结合的研究方法，研究自锚试桩与传统试桩的荷载传递规律、土中应力分布规律的差异特征及桩承载力转换特性。主要研究内容及创新点：（1）研究不同加载方式引起的土中应力分布规律，建立考虑桩土相互影响的自锚试桩桩身及桩端荷载传递函数；（2）建立不同加载方式引起的桩侧摩阻力对桩端承载力影响模型；（3）揭示自锚试桩荷载传递机理，建立自锚试桩承载力转换计算模型；（4）根据数值模拟、相似模拟，建立确定平衡点位置的理论方法。. 本项目的成果揭示自锚试桩的受力变形特性，丰富并发展桩基测试理论，为自锚试桩的推广应用提供理论支撑。

采用室内模型试验、原位试验、解析解推导、数值模拟计算等方法，对竖向抗拔桩、桩端无土竖向抗压桩、桩端有土抗压桩（传统静载荷试验桩）、自锚试桩等进行了系统的试验研究及理论研究。发现竖向抗拔桩发挥桩侧摩阻力需要的位移量小于桩端无土竖向抗压桩的位移量，据此定义了自锚试桩上段桩的位移转换公式；对桩端有土抗压桩（传统静载荷试验桩）的研究表明，桩侧摩阻力先于桩端阻力发挥，桩侧摩阻力发挥的Q-s曲线接近线性分布，当桩侧摩阻力发挥到90%以上时，桩端阻力才会有明显的发挥，桩端阻力发挥后，Q-s曲线则转变为非线性分布，由此提出了自锚试桩Q-s曲线向传统静载荷Q-s曲线的二段转换法；通过桩周土附加应力的定量研究发现，自锚试桩加荷载时，上段桩对下段桩的影响、下段桩对上段桩的影响可以忽略不计，这为将自锚试桩上、下段桩承载力转换为传统静载荷试验整桩承载力提供了依据。自锚试桩研究成果可直接应用于高承载力桩的检测，是一种低碳、节约、高效、安全的基桩承载力测试方法。