3种模式下钻孔灌注桩桩-土剪切特性现场试验研究

Shear properties of pile-soil of three modes of bored piles in field tests

不同的桩-土剪切模式对桩-土剪切位移量的大小和桩侧摩阻力的发挥有重要影响。对抗压桩、顶拔桩和负摩擦桩等3种模式的6根钻孔灌注桩的剪切特性进行了现场加载试验与长期监测。通过对不同桩型的桩身应变、桩顶位移和桩周土沉降等试验资料的系统分析,建立了"侧阻-位移"曲线确定各模式桩-土剪切位移量和不同深度的极限侧阻力。根据不同桩-土剪切模式极限侧阻力的发挥特征,分析了桩-土相对运动方向、剪切边界约束条件、剪切位移量、加载速率和剪切历时等5个因素对极限侧阻力发挥的不同影响。讨论了利用现场顶拔桩试验结果对桩负摩阻力增大段的极限负摩阻力进行预测的可行性,供同行参考借鉴。

The pile-soil shear modes have significant influences on the displacement of pile-soil shear and the development of pile side resistance. Field experiments and long-term monitoring were carried out to study shear properties of six bored piles under three modes: bearing pile type, uplift pile type and negative friction pile type. The curve of side resistance versus displacement was established by systematically analyzing the pile strain, displacement of the top pile, and pile-soil layered subsidence of different pile types. The established curve was further used to determine the displacement of pile-soil shear in different modes and the ultimate lateral resistance at different depths. According to the characteristics of the ultimate lateral resistance in different modes, its five influence factors were analyzed, including the relative motion direction of pile-soil, shearing boundary constraint, shear displacement, loading rate and shear duration. Meanwhile, we discussed the feasibility of using the in situ testing results of uplift pile to predict the ultimate lateral resistance of negative friction pile in the increasing stage. This study provides useful references for similar projects.