全夯式多头混凝土扩灌桩单桩竖向承载机理研究

发布时间：2018-02-26 21:29

本文关键词： 变截面桩荷载传递机理静载荷试验室内模型试验扩大头　出处：《东华理工大学》2017年硕士论文　论文类型：学位论文

【摘要】：全夯式多头混凝土扩灌桩具有挤密桩周围土体、增大桩身和桩端作用面积的作用。它在各类型的建筑工程中改进了传统的地基基础的处理方式,它具有承载力高、稳定性强的优点,可以改善不均匀沉降,具有良好的性能。然而在其工程应用过程中在承载机理、承载力计算方法、夯扩挤密效果等方面仍然存在一些问题,针对单桩竖向承载机理问题本文将展开深入的研究。首先,通过室内模型试验,针对全夯式多头混凝土扩灌桩的荷载沉降曲线、桩周土体的挤密影响范围和不同扩大头间距进行了研究,在均质砂土、均质黏土场地条件下与夯扩桩和普通直桩相比较,根据土压力计的测试结果显示,土体压力在桩端扩大头正下方是荷载最大,其次就是斜下方的位置,最后就是扩大头的纵方向处,扩大头之间的距离应大于2倍扩大头直径为宜;在施加荷载阶段,荷载沉降曲线前期变化比较平缓,继续荷载的增加荷载沉降曲线表现为“双峰”,显示出了桩身扩大头和桩端扩大头分散荷载,增大单桩竖向承载力的影响。其次,本文利用有限差分分析软件对全夯式多头混凝土扩灌桩扩大头之间的距离对荷载传递的影响、桩周围土体的应力应变和桩身轴力变化进行了分析。通过与普通直桩和夯扩桩之间的分析结果可知,其极限单桩承载力约为普通直桩的1.5~2.5倍,夯扩桩的1~1.5倍;砂土中扩大头周围土体的应力向下和向两侧扩散均比较明显,土体的应力在扩大头上下位置变化很大,扩大头下方土体承担了较多的荷载;在对桩顶加载过程中,扩大头顶部出现扩张带;地基土为均质土体时该桩型破坏模式为刺入破坏。再次,将现场试验数据与理论及模型试验作对比,该数据和理论计算分析的结果相符合,揭示出了荷载的传递特性,同时也进一步验证了承载力计算方法的合理性。最后,本文对全夯式多头混凝土扩灌桩的荷载传递的规律进行了理论分析,其主要通过全夯式多头混凝土扩灌桩竖向受压承载机理、破坏模式、桩身扩大头阻力影响分析以及桩端扩大头阻力影响分析等方面进行分析,得出了其单桩竖向承载的相关因素和特点并将承载传递机理与工程实践相结合,考虑多重因素推导出相对合适的全夯式多头混凝土扩灌桩单桩竖向承载力计算公式。
[Abstract]:Full compaction concrete expansion grouting pile has the function of soil around compaction pile and increasing the action area of pile body and pile tip. It improves the traditional treatment method of foundation foundation in all kinds of construction projects, and it has high bearing capacity. The advantages of strong stability can improve uneven settlement and have good performance. However, there are still some problems in carrying mechanism, calculation method of bearing capacity, compaction and compaction effect in engineering application. In this paper, the vertical bearing mechanism of single pile will be studied deeply. Firstly, through indoor model test, the load settlement curve of full rammed multi-head concrete pile is studied. The influence range of compaction of soil around pile and the distance between different enlarged heads are studied. Compared with rammed pile and ordinary straight pile in homogeneous sand and homogeneous clay soil, the test results of soil pressure gauge show that, The pressure of the soil is the largest at the end of the pile, followed by the position below the slope. Finally, the longitudinal direction of the head is enlarged. The distance between the enlarged heads should be more than 2 times the diameter of the head; at the stage of loading, the distance between the enlarged heads should be more than 2 times the diameter of the head. The initial variation of load settlement curve is relatively gentle, and the increasing load settlement curve of continuous load is shown as "double peak", which shows the influence of spreading load on the enlarged head of pile body and on the expanded head of pile end, which increases the vertical bearing capacity of single pile. In this paper, the finite difference analysis software is used to analyze the influence of the distance between the expansion and grouting piles of full rammed multi-head concrete on the load transfer. The stress and strain of the soil around the pile and the axial force of the pile body are analyzed. The results of the analysis with the ordinary straight pile and rammed pile show that the ultimate bearing capacity of the single pile is about 1.52.5 times of that of the ordinary pile, and that of the rammed pile is 1 / 1.5 times of that of the rammed pile. The stress of the soil around the expanded head in sand is obviously diffused down and to both sides. The stress of the soil changes greatly in the upper and lower position of the expanded head, and the soil under the expanded head bears more loads; in the process of loading the pile top, The expansion zone appears at the top of the enlarged head, and the pile failure mode is pierced when the foundation soil is homogeneous soil. Thirdly, the field test data are compared with the theoretical and model tests, and the results of the theoretical calculation and analysis are consistent. The characteristics of load transfer are revealed, and the rationality of the calculation method of bearing capacity is further verified. Finally, the law of load transfer of fully rammed multi-head concrete pile is theoretically analyzed in this paper. It is mainly analyzed from the aspects of the mechanism of vertical compression bearing, failure mode, the influence analysis of the resistance of the enlarged head of pile body and the influence analysis of the resistance of the expanded head of pile end, etc. The related factors and characteristics of vertical bearing capacity of single pile are obtained, and the bearing transfer mechanism is combined with engineering practice. Considering multiple factors, a relatively suitable formula for calculating vertical bearing capacity of single pile with full tamping concrete expansion pile is derived.
【学位授予单位】：东华理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU473.1

【参考文献】