考虑桩端与桩侧阻力相互作用的超长桩承载力研究

发布时间：2018-04-02 11:11

本文选题：超长桩　切入点：承载特性　出处：《辽宁工程技术大学》2015年硕士论文

【摘要】：近年来高层建筑、大型桥梁、港口等建设中广泛应用大直径超长桩,给桩基理论这一传统课题提出了新的挑战。研究发现当桩顶受荷水平临近极限承载力时,超长桩桩端附近摩阻力有突然增大的现象,且在不同桩周土强度与桩土接触面性质的影响下,这种增大效果的发挥也不同。深入研究此种增强作用的原因及机理,对超长桩的理论研究和实际应用具有十分重要的意义。本文设计实施了超长桩室内模型试验,分析了模型桩在不同桩顶荷载下荷载与沉降的关系、桩身轴力随深度的变化、桩侧摩阻力随深度的变化以及桩顶荷载与桩端土压力的关系。利用ADINA软件建立了对应于模型试验的有限元模型,将有限元模拟结果与试验结果进行对比分析,并研究了桩端阻力与桩侧阻力相互作用的机理。在考虑桩侧阻力与桩端阻力的相互作用的基础上,提出用Mindlin解对桩侧阻力增强值进行计算,并结合弹性理论法对模型桩承载力进行了计算,对比了模型桩桩侧摩阻力修正前后的计算结果。通过以上研究,得到了如下结论：(1)超长桩的桩顶沉降较大,在设计超长桩的极限承载力时,以沉降控制较为合理；竖向荷载沿超长桩桩身向下传递的过程中,上部桩侧土分担了较多的桩顶荷载,桩端承受的荷载相对较小；超长桩桩侧摩阻力发挥作用的主要部位在桩身上部以及桩底以上10d范围内,桩身中部侧摩阻力相对较小。当桩顶荷载增加至一定值时,桩端附近出现侧摩阻力增强现象；在桩顶荷载达到1093N时,试验模型桩的桩端阻力和桩侧阻力在桩端附近均出现增强现象。(2)有限元模拟可以反映出超长模型试验中桩土作用的实际情况；桩端阻力对桩侧土的水平应力有增强作用,增大范围约为桩端以上5d范围内；桩侧阻力对桩端土5d范围内的应力也具有增强作用,提高了桩端土的极限承载力；桩侧阻力对桩端阻力的强化作用并不明显,考虑桩端与桩侧阻力相互作用的超长桩承载力计算,关键在于准确计算桩侧阻力的增强值。(3)应用Mindlin解对桩端阻力产生的桩侧水平应力进行计算,并根据滑动摩擦力与法向应力呈直线关系,得到了考虑桩端阻力作用下的桩侧附加摩阻力计算方法。(4)当桩顶作用荷载较大时,弹性理论法计算的桩侧摩阻力与试验值在桩端附近存在偏离。结合附加侧摩阻力进行修正后得到的计算侧摩阻力与试验值接近,说明此种计算方法对正确计算超长桩的侧摩阻具有一定的理论意义和工程价值。
[Abstract]:In recent years, large diameter super-long piles have been widely used in high-rise buildings, large bridges, ports and so on, which presents a new challenge to the traditional problem of pile foundation theory. It is found that when the load level of pile top is near the ultimate bearing capacity, The frictional resistance near the end of super-long pile increases suddenly, and under the influence of different soil strength around pile and pile-soil interface, the effect of this increase is also different. It is very important for the theoretical research and practical application of super-long pile. In this paper, the indoor model test of super-long pile is designed and implemented, and the relationship between load and settlement of model pile under different pile top loads is analyzed, and the axial force of pile body changes with depth. The variation of pile side friction with depth and the relationship between pile top load and soil pressure at the end of pile are studied. The finite element model corresponding to the model test is established by using ADINA software, and the results of finite element simulation and test are compared and analyzed. The mechanism of interaction between pile end resistance and pile side resistance is studied. On the basis of considering the interaction between pile side resistance and pile end resistance, the Mindlin solution is proposed to calculate the pile side resistance enhancement value. Combined with elastic theory, the bearing capacity of model pile is calculated, and the calculated results before and after the modification of frictional resistance on the side of model pile are compared. Through the above study, it is concluded that the settlement of the pile top of the super-long pile is larger than that of the super-long pile. In the design of ultimate bearing capacity of super-long pile, the settlement control is more reasonable, and in the process of vertical load passing down the pile body, the upper pile side soil shares more pile top load, and the load on the pile end is relatively small. The main part of the lateral friction of super-long pile is in the pile body and above the pile bottom for 10 days, the friction of the middle side of the pile is relatively small. When the load on the top of the pile increases to a certain value, the phenomenon of increasing the side friction near the pile end appears. When the load on the top of the pile reaches 1093N, both the pile tip resistance and the lateral resistance of the test model pile are enhanced near the pile tip. The finite element simulation can reflect the actual situation of pile-soil action in the super-long model test. The resistance at the end of the pile enhances the horizontal stress of the soil on the side of the pile, the increasing range is about 5 days above the end of the pile, and the resistance of the side of the pile also increases the stress in the range of 5 days, which improves the ultimate bearing capacity of the soil at the end of the pile. The reinforcement effect of pile side resistance on pile tip resistance is not obvious. The bearing capacity of super-long pile considering the interaction between pile end and pile side resistance is calculated. The key lies in accurately calculating the enhancement value of pile side resistance. The Mindlin solution is used to calculate the horizontal stress of pile side caused by resistance at the end of the pile, and according to the relationship between sliding friction force and normal stress, the horizontal stress of pile side is calculated in a straight line. The calculation method of additional frictional resistance of pile side considering the resistance of pile tip is obtained. 4) when the load on the top of pile is large, The pile side friction calculated by the elastic theory method deviates from the test value near the pile end, and the calculated side friction resistance is close to the test value after modified with the additional side friction. It is shown that this method has certain theoretical significance and engineering value for correctly calculating the lateral friction of super-long piles.
【学位授予单位】：辽宁工程技术大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TU473.1

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