混凝土—土界面剪切特性及自平衡法试桩研究

发布时间：2018-03-24 12:23

本文选题：自平衡试桩法　切入点：荷载传递机理　出处：《长沙理工大学》2014年硕士论文

【摘要】：自平衡试桩法是一种特殊装置下的静载荷试验,但是在实际工程测试中由于平衡点位置比较难确定,导致其中一段桩达到极限承载力时另外一段桩并未达到,最终难以得到科学的测试结果。为此,本文基于自平衡测桩法基本原理及其存在的主要问题、下压桩和上托桩的荷载传递机理及其差别,通过直剪试验,研究全风化花岗岩填土一混凝土界面剪切特性,为科学评判自平衡试桩法测桩结果提供试验依据。本论文主要结论有：(1)对于下压桩来说,摩阻力沿深度的分布形式是外凸形,桩身荷载和桩身轴向变形随深度递减。对于上托桩而言,摩阻力沿深度的分布形式是内凹形,桩身荷载和桩身轴向变形随距桩底的距离递减。(2)直剪试验结果表明：平整接触面抗剪强度为粗糙接触面抗剪强度的75.8%-94.7%;21天的抗剪强度比14天的抗剪强度提高6.4%-15.6%;泥皮接触面的抗剪强度约为无泥皮时抗剪强度的90%。本文得到了多种接触面条件下剪应力与剪切位移的关系曲线,为自平衡试桩法中未达到极限状态的那段桩提供依据,确定该桩-土界面破坏时的桩侧摩阻力,进而反算出其极限承载力。(3)自平衡法测桩结果表明：桩身轴力曲线以荷载箱为分界,在荷载箱处轴力最大,向上和向下轴力均减小。对于强风化花岗岩,单位正摩擦力随荷载增大而增大,实测值要远大于根据碎石类土的初定值。当荷载增加时,负摩阻力和正摩阻力的比值也相应变大,在本次试验时其比值在0.7-0.9之间变化。下段桩的加载-位移曲线呈缓变型,位移较小,未达到极限状态,不能准确得到其极限承载力。
[Abstract]:The self-balancing pile test method is a static load test under a special device. However, in the actual engineering test, the position of the equilibrium point is difficult to be determined, which results in the failure of the other section of the pile to reach the ultimate bearing capacity when one of the piles reaches the ultimate bearing capacity. Finally, it is difficult to obtain scientific test results. Therefore, based on the basic principle of self-balanced pile method and its main problems, the load transfer mechanism and its difference between the lower pressure pile and the upper supporting pile, the direct shear test is carried out in this paper. The shear characteristics of fully weathered granite filled with concrete interface are studied, which provides the experimental basis for scientifically judging the results of self-balanced pile test. The main conclusion of this paper is that the distribution of frictional resistance along the depth of the pile under pressure is in the form of protruding, the main conclusion of this paper is: (1) for the pile under pressure, the distribution of frictional resistance along the depth is convex. The load of pile body and axial deformation of pile body decrease with the depth. The results of direct shear test show that the shear strength of flat contact surface is 75.8% -94.7% of the shear strength of rough contact surface, and the shear strength of 21 days is 6.4- 15.6m higher than that of 14 days; the shear strength of the smooth contact surface is increased by 6.4-15.60.The shear strength of the pile body and the axial deformation of the pile body decreases with the distance from the bottom of the pile to the bottom of the pile. The shear strength of the contact surface is about 90% of that of the shearing strength without mud. In this paper, the relationship between shear stress and shear displacement under various contact conditions is obtained. It provides the basis for the pile which has not reached the limit state in the self-balanced pile test method, and determines the pile side friction when the pile-soil interface is destroyed. The results show that the axial force curve of the pile body is the boundary of the load box, and the axial force at the load box is the largest, and the upward and downward axial forces are both decreased. For the strongly weathered granite, the axial force of the pile is measured by the self-equilibrium method, and the maximum axial force is obtained at the load box, and the upward and downward axial forces decrease. The unit positive friction force increases with the increase of load, and the measured value is much larger than the initial value of gravel soil. When the load increases, the ratio of negative friction resistance to positive friction resistance increases correspondingly. The load-displacement curve of the pile in the lower section of the pile is slowly changed, the displacement is small, and the ultimate bearing capacity can not be accurately obtained because the ratio is between 0.7-0.9 in this experiment.
【学位授予单位】：长沙理工大学
【学位级别】：硕士
【学位授予年份】：2014
【分类号】：TU473.1

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