细粉砂含水率对扩盘桩抗拔破坏状态的影响研究

发布时间：2018-04-30 05:43

本文选题：混凝土扩盘桩 + 细粉砂　；参考：《吉林建筑大学》2017年硕士论文

【摘要】：混凝土扩盘桩是由单个或多个承力盘和多段等截面桩身组成的。正是由于桩身的盘体及盘上土体的相互作用,使得混凝土扩盘桩的承载力相比传统的等截面桩有很大的提高。除此之外,混凝土扩盘桩还具有减小基础位移、适用范围广泛、节约成本等优点。因此对于该新型桩基础有必要进行深入的研究,以有利于应用推广。本论文主要针对细粉砂土进行混凝土扩盘桩受力状态的研究,第一,控制细粉砂含水率为单一变量,通过小模型半截面桩埋土试验研究,观察模型桩在竖向拉力作用下单桩极限抗拔承载力和桩周土体的破坏性状等,研究表明:在模型加载前期,扩大盘与盘下土体出现分离,盘端出现水平裂缝,扩大盘上部土体局部受压,逐渐被压密实;随着荷载的逐渐增大,盘上受压土体边缘发生滑移破坏,在盘上一定范围内开始回收,形成圆弧状的滑移曲线,并且带动上部土体发生滑动,在桩两侧沿45°方向对称斜裂缝逐渐发展,直至裂缝范围内的整体砂土发生冲切破坏,模型宣告破坏;根据试验结果,当细粉砂含水率高于15%时,混凝土扩盘桩的承载力较低,而当细粉砂含水率低于15%左右时,混凝土扩盘桩的承载能力较高;第二,根据试验后取样测得的细粉砂含水率及抗剪强度等参数,利用ANSYS有限元软件进行模拟计算,分析在不同含水率情况下混凝土扩盘桩的荷载位移、应力和应变等结果,研究表明:当含水率超过15%时,扩盘桩的抗拔承载力明显降低,而且桩顶竖向位移较大;这充分说明了由于细粉砂土颗粒之间的粘聚力较低,含水率越大,细粉砂的承载能力越低。第三,通过将试验模型与有限元模型对比,发现在误差允许的范围内,试验结果和有限元模拟结果相对吻合;并且探讨了冲切破坏和滑移破坏两种计算模式,得出承土器表面有无约束时混凝土扩盘桩单桩极限承载力的计算方法,进而对单桩极限承载力计算公式进行修正。本论文通过研究细粉砂含水率对混凝土扩盘桩抗拔承载能力及桩周土体破坏状态的影响,在一定程度上完善了混凝土扩盘桩单桩极限抗拔承载力的理论结果。
[Abstract]:Concrete pile is composed of single or multiple load-bearing plates and multi-section piles with equal cross-section. It is precisely because of the interaction between the plate body of the pile body and the soil on the plate that the bearing capacity of the concrete pile with expanded plate is greatly improved than that of the traditional equal-section pile. In addition, concrete pile also has the advantages of reducing foundation displacement, wide range of application and cost saving. Therefore, it is necessary to further study the new pile foundation in order to facilitate its application and popularization. In this paper, the stress state of concrete pile is studied. Firstly, controlling the moisture content of fine silt is a single variable, and the experimental study of soil buried by small model semi-section pile is carried out. The ultimate pull-out bearing capacity of the model pile and the destructive behavior of the soil around the pile are observed. The results show that in the early stage of the model loading, there is separation between the enlarged plate and the soil under the plate, and horizontal cracks appear at the end of the plate. With the increasing of the load, the edge of the compressed soil on the disk will slip and destroy, and start to recover in a certain range on the disk, and form a circular slip curve. And driving the upper soil body to slide, the symmetrical oblique crack develops gradually along 45 掳direction on both sides of the pile, until the whole sand within the crack range is flushed and destroyed, the model is declared to be destroyed. According to the test results, when the moisture content of fine silt is higher than 15, The bearing capacity of concrete pile is low, but when the moisture content of fine silt is lower than 15%, the bearing capacity of concrete pile is higher. Secondly, according to the parameters such as moisture content and shear strength of fine silt, ANSYS finite element software is used to simulate and calculate the load displacement, stress and strain of concrete pile with different moisture content. The results show that when the moisture content exceeds 15, the uplift bearing capacity of the pile decreases obviously. The vertical displacement of the top of the pile is larger, which fully shows that because of the low cohesion between fine silt particles, the higher the moisture content, the lower the bearing capacity of fine silt. Thirdly, by comparing the test model with the finite element model, it is found that the experimental results are in good agreement with the finite element simulation results within the range of error, and the two calculation models of punching failure and slip failure are discussed. The calculation method of ultimate bearing capacity of single pile with or without constraint on the surface of earth-bearing device is obtained, and the formula for calculating ultimate bearing capacity of single pile is modified. In this paper, the influence of fine silt moisture content on the uplift bearing capacity of concrete pile and the failure state of soil around the pile is studied. To some extent, the theoretical results of ultimate pull-out bearing capacity of concrete pile are improved.
【学位授予单位】：吉林建筑大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TU473.1

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