大直径变截面桩速度波衰减特性研究与应用

针对大直径桩在低应变测试中的三维效应和缺陷量化分析问题,建立变截面桩–成层土耦合振动模型,考虑桩身的三维波动,通过建立层间递推关系求解得到桩身任意位置纵向振动响应的频域解析解,并利用傅里叶逆变换得到时域内半解析表达。在此基础上,分别针对完整桩和缺陷桩,探讨不同条件下桩身入射速度波沿径向和纵向的幅值和走时变化规律。最后通过现场试验对某混凝土灌注桩的桩顶及桩身内部纵向振动响应进行测试,验证了本文解的合理性。理论与试验结果表明:(1)中心瞬态激振条件下大直径桩的三维效应显著,其影响深度与桩顶激振力的作用面积和持续时间相关;(2)速度波沿桩身的纵向衰减特性能够较好地反映出桩身完整性和桩侧土阻力特性,这一研究结果能够为基桩完整性检测提供一种新的思路和方法,具有一定的工程应用价值。

Velocity wave attenuation characteristics of large-diameter variable section piles and the application

This study focuses on the three-dimensional effect and defect quantitative analysis method of large-diameter piles in low strain integrity test. A coupling vibration model of variable cross-section piles and surrounding layered soil was proposed. A frequency-domain analytical solution of the longitudinal vibration response at any position of the pile,considering the three-dimensional fluctuation of the pile body,was obtained by establishing a recurrence relationship between the layers,and a semi-analytical solution in time domain was deduced with inverse Fourier transform. Then the amplitude attenuation and travel time of the incident velocity wave along radial or longitudinal directions of the pile under different conditions were discussed. Finally,a field test was carried out to investigate the longitudinal vibration response at different positions of a concrete pile,and the rationality of the analytical solutions was verified. The results show that the three-dimensional effect of a large-diameter pile in low strain integrity test is significant and the influence depth is related to the action area and duration of the excitation force on the pile top. The longitudinal attenuation characteristics of the velocity wave can well reflect the integrity of the pile body and the surrounding soil resistance. The research work provides a new method for testing the integrity of piles and has certain engineering application value.