DOI: 10.15986/j.1006-7930.2020.01.005
为了解扩底抗拔桩的承载特性和桩身内力的分布.本文通过室内模型试验研究了长径比、桩身表面粗糙程度这两个因素对扩底桩极限抗拔承载力、桩身轴力和桩侧摩阻力分布的影响,并与等截面桩进行了对比研究.结果表明:(1)当桩身长径比L/d为15和40时,扩底桩能显著提高等截面桩的极限抗拔承载力,提高幅度为30.8%～85.7%.(2)扩底桩抗拔力主要由等截面段桩侧摩阻力和扩大头抗力两部分构成,前者占总抗拔承载力比重随加载的增加而线性减小,后者占总抗拔承载力比重随加载的增加而线性增大.极限状态时,对L/d=15与40的扩底桩,扩大头抗力占总抗拔极限承载力的比例分别为50%和35%.(3)扩底桩在桩端附近的轴力小于等截面桩,且轴力值随加载的增加呈线性增长趋势.(4)扩底桩在桩端附近的桩侧摩阻力由于扩大头的侧向挤土效应而显著大于等截面桩对应位置处的侧摩阻力.极限状态时,前者的值约为后者的3.8倍.(5)当扩底桩达到极限抗拔承载力时,扩底桩在桩端附近处的桩侧摩阻力未达到最值,有进一步增大的趋势.该研究成果可为扩底抗拔桩的桩身结构设计提供有益参考.
In order to reveal the bearing deformation behavior of uplift pedestal piles in sand, model experiments were conducted in sand to investigate the impact of the length to its diameter and the roughness of pile-soil interface on the bearing capacity, axial force and friction resistance of pile side. And the group of straight-shaft piles were set in comparison. The results show that:(1)when the L/d=15 and 40, the bearing capacity of straight-shaft pile with enlarged base can be improved and the improving range from 30.8% to 85.7%.(2)the bearing capacity of pedestal pile mainly consists of two parts: the friction resistance of pile side of the equal section, and the resistance of the enlarged base. The former decreases linearly with the increase of the load and the latter increases linearly with the increase of the load. When the bearing capacity increases to its maximum, the sharing portions of the enlarged base are about 50% and 35% for the pedestal pile in L/d=15 and 40.(3)the axial force at the end of the pedestal pile is lager than the same position of the straight-shaft pile, and the value of it increases linearly with the increase of loading.(4)the side friction resistance of the enlarged section of the pedestal pile is larger than the corresponding section of the straight-shaft pile owing to the lateral squeezing effect of the enlarged base, and the side friction resistance of the former is about 3.8 times the latter when the bearing capacity reach the maximum.(5)when the bearing capacity reaches the maximum, the side friction near the pile end of the pedestal pile does not appear softening, and there is a tendency to further increase. The conclusions drawn from the study can provide valuable references for the structure design of uplift pedestal piles.
