多节钻扩灌注桩最优构造与竖向承载力理论研究

发布时间：2018-05-27 21:45

本文选题：多节钻扩灌注桩 + 构造优化　；参考：《山东大学》2017年硕士论文

【摘要】：变径灌注桩以其高承载力、施工简易等特点越来越多的应用于工程建设中。多节钻扩灌注桩作为一种支盘桩、DX桩的优化发展桩型,其成桩质量可靠,施工效率高,承载力提高显著,但是其桩身构造设置和竖向承载力机理亟待开发与研究,本文采用数值模拟并结合理论分析的方法,研究并完善了钻扩桩构造优化设置及竖向承载力理论,取得结论如下:1、基于理论推导,明确了钻扩桩扩径体剖面几何形状为星形线与圆弧组合而成,推导了具体扩径体几何形状的数学模型公式;通过对比模型试验,判断出钻扩桩最佳盘径桩径比D/d取值宜为2～2.5,单桩最佳扩径体数量约为2～3个,且宜设置在靠下的坚硬土层上,相邻扩径体最小间距约为2.5D～3.5D。2、通过对比分析,发现钻扩桩抗压时,扩径体上部影响段摩阻力产生软化减小,下部影响段产生硬化增大,综合而言,设置扩径体后承载力得到增强,但扩径体对其临近侧摩阻力产生弱化效应;考虑扩径体对邻近区域摩阻力的影响,提出新型抗压承载力计算公式,验证结果良好。3、结合荷载传递法,取桩侧、桩端、扩径端为双曲线函数,求解出钻扩桩非线性沉降预测方法,并对侧阻参数进行变量分析;在扩径端引入圆孔扩张理论,推导分析出考虑扩径体几何特征的扩径端力与位移关系,得出受压面水平内压力ph的分布规律;在此基础上应用荷载传递法,重新计算出桩顶沉降曲线,并与前者对比,发现新方法相对于传统方法能更精准的预测中前期桩顶沉降,更能体现承载力对扩径体特征的敏感性,传统方法得到的扩径端阻力小于实际值,但可以考虑塑性屈服,存在极限值,而新方法由于未考虑塑性条件,仅有弹性情况,使得其对扩径端阻力的后期预测明显偏大,后期沉降值会小于实际值。4、通过对比分析,发现钻扩桩抗拔时,扩径体上部影响段摩阻力产生硬化增大,下部影响段产生软化减小,综合而言,抗拔扩径体对其临近侧摩阻力产生强化效应;考虑扩径体对邻近区域摩阻力的影响,提出新型抗拔承载力计算公式,验证结果良好。
[Abstract]:Variable diameter cast-in-place pile is more and more widely used in engineering construction because of its high bearing capacity and easy construction. As a kind of optimum development pile type of branch disc pile and DX pile, multi-section drilling-expansion pile is of reliable quality, high construction efficiency and remarkable improvement of bearing capacity. However, the structure of pile body and the mechanism of vertical bearing capacity need to be developed and studied urgently. In this paper, numerical simulation and theoretical analysis are used to study and perfect the theory of structural optimization and vertical bearing capacity of drilling-expanding pile. The conclusions are as follows: 1, based on theoretical derivation. In this paper, it is clear that the geometric shape of the expanding body section of drill pile is the combination of star line and circular arc, the mathematical model formula of the geometric shape of the concrete expanding body is derived, and the comparison model test is carried out. It is found that the optimum diameter ratio D / d is 22.5, and the optimum number of single pile is about 2 ~ 3, and the minimum distance of adjacent diameter expanding is about 2.5 DX 3.5D.2. it is found that when drilling and expanding piles are compressed, the minimum distance between them is about 2.5 DX 3.5D.2.The results show that the optimum diameter ratio is about 2.5 DX / d, and the optimum diameter expansion is about 2 ~ 3, and the minimum distance between the two piles is about 2.5 DX 3.5D.2. The frictional resistance of the upper part of the expanding body decreases, and the lower part of the body harms and increases. In a word, the bearing capacity of the upper part of the expanding body is enhanced, but the effect of the expanding body on the adjacent side friction is weakened. Considering the influence of the expanding body on the frictional resistance of the adjacent region, a new formula for calculating the compressive bearing capacity is put forward. The result is good .3. combined with the load transfer method, the pile side, the pile end and the expanding end are taken as hyperbolic functions. The nonlinear settlement prediction method of drilling and expanding pile is solved, and the variable analysis of lateral resistance parameter is carried out, and the expansion theory of circular hole is introduced into the expanding end, and the relationship between the expanding end force and displacement considering the geometric characteristics of the expanding body is deduced and analyzed. On the basis of this, the settlement curve of pile top is recalculated by using load transfer method, and compared with the former, it is found that the new method can predict the settlement of pile top more accurately than the traditional method The resistance of the traditional method is smaller than the actual value, but the plastic yield can be considered and the limit value exists. However, the new method is only elastic because it does not consider the plastic condition. The later prediction of the resistance to the expanding end is obviously larger, and the later settlement value will be less than the actual value .4.Through comparison and analysis, it is found that the friction of the upper influence section of the expanding body increases while the lower part of the expanding pile softens when the pile is pulled out. To sum up, the anti-pull-out expanding body has a strengthening effect on the frictional resistance of the adjacent side, and considering the influence of the expanding body on the frictional resistance of the adjacent region, a new formula for calculating the pull-out bearing capacity is put forward, and the results are good.
【学位授予单位】：山东大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU473.1

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