【作者】 袁伟；

【导师】 朱小军； 朱克平；

【作者基本信息】 扬州大学 ， 工程（专业学位）， 2020， 硕士

【摘要】 随着城市化的快速发展,土地资源需求量急剧增多,地下空间的发展成为了一个新的趋势,为了解决地下空间的抗浮问题,设置抗拔桩基础成为了重要措施。本文主要采用的室内模型试验,对抗拔桩在砂土中的抗拔特性进行研究,主要的研究内容和结论如下:(1)进行等截面半模桩试验,结果得出:土体的竖向位移沿桩体自上而下逐渐增大,位移集中区处在在桩端,模型桩在砂土中的破坏模式为圆柱剪切破坏。(2)进行等截面单桩抗拔试验,发现随着桩的长径比逐渐增加,等截面单桩的抗拔极限承载力也逐渐增大。在相同的上拔荷载下,长径比小的上拔位移大于长径比大的。桩身轴力自上而下逐渐减小,在桩长20cm时,桩侧摩阻力分布呈“两头大、中间小”的变化,其余桩长情况下的桩侧摩阻力随长径比的增加而增大,其峰值集中在桩身中下部位置。(3)进行群桩抗拔试验,结果表明:群桩与单桩的荷载位移曲线的规律基本相同,上拔位移会随着桩间距和桩数的增加而增加。在不同桩间距、桩长以及桩数的情况下群桩效应系数均都小于0.6。群桩的桩身轴力分布规律与单桩基本一致,都呈现出“上宽下窄”的分布规律。桩间距的不同,桩侧摩阻力达到峰值的深度也不同。桩长较短时,桩侧摩阻力先发挥作用,桩长较长时,桩侧摩阻力呈现出先小后大,再到小的变化趋势。(4)在五种不同计算单桩抗拔极限承载力方法中,规范法与试验值最为接近。而在计算群桩抗拔承载力的方法中,发现抗拔承载力的大小会受到桩间距、桩长以及桩数的影响,还要注意公式中的重要参数,其取值的方式会接影响计算结果。使用规范法和Patra模型在各自特定情况下预估抗拔极限承载力相对于回归公式法更接近于试验值。更多还原

【Abstract】 With the rapid development of urbanization,the demand for land resources has increased dramatically,and the development of underground space has become a new trend.In order to solve the anti-floating problem of underground space,setting up anti-pile foundations has become an important measure.This article mainly uses indoor model tests to study the existence characteristics of uplift piles in sand.The main research contents and conclusions are as follows:(1)Carrying out the test of equal section half-mold piles,the results show that the vertical displacement of the soil gradually increases along the pile from top to bottom,the displacement concentration area is at the pile end,and the failure mode of the model pile in the sand It is a cylindrical shear failure.(2)The uplift test of a single pile of equal cross section was carried out,and it was found that as the length-to-diameter ratio of the pile gradually increased,the uplift ultimate bearing capacity of the single pile of equal cross section gradually increased.Under the same uplift load,the uplift displacement with a small aspect ratio is greater than that with a large aspect ratio.The axial force of the pile body gradually decreases from top to bottom.Except for the pile length of 20 cm,the friction resistance of the pile side is "big at both ends and small in the middle".The friction resistance of the other piles increases with the increase of the length-to-diameter ratio.The peak value is concentrated in the middle and lower part of the pile body.(3)The uplift test of the group piles shows that the load-displacement curve of the group piles and the single pile is basically the same,and the uplift displacement will increase with the increase of the pile spacing and the number of piles.Under the conditions of different pile spacing,pile length and pile number,the pile group effect coefficients are all less than 0.6.The distribution law of the axial force of the pile body of the group pile is basically the same as that of the single pile,and they all show the distribution rule of "upper width and lower width".The depth of the peak frictional resistance of the pile is different depending on the distance between the piles.When the length of the pile is short,the frictional resistance of the pile side comes into play first.When the length of the pile is long,the frictional resistance of the pile side is firstly small,then large,and then small.(4)Among the five different methods for calculating the ultimate bearing capacity of single piles,the code method is closest to the test value.In the method of calculating the uplift bearing capacity of group piles,it is found that the size of uplift bearing capacity will be affected by the pile spacing,pile length and number of piles,and also pay attention to the important parameters in the formula,and the way of its value will be affected.Calculation results.The normalized method and the Patra model are used to estimate the ultimate pull-out bearing capacity in each specific case,which is closer to the test value than the regression formula method.更多还原