低应变检测中振源及桩土相互作用的影响分析

敲击-回波法是基桩完整性检测的有效方法，基于一维应力波理论，可以根据桩顶反射波质点振动速度响应曲线（包括走时、幅值及相位）来确定桩体波阻抗变化范围及程度。然而，在实际中，桩是柱体而非杆件，截面变形不均匀。通过点源激发的波分量及在桩顶侧面的反射波，分析了桩顶近场三维波动现象，并基于圆柱中纵向波对远场波进行分析。结果表明，在测点位置及激振频率满足一定的要求时，三维波动特性及纵向波频散特性可以削弱，桩的动测信号可近似用一维应力波理论来分析。在桩土相互作用下，桩体中应力波随传播衰减，分析了桩土剪切波速差异对应力波衰减影响规律，结果表明，应力波衰减不仅与桩土剪切波速比值有关，而且还与桩土剪切波速绝对值有关，桩体剪切波速越低、土体剪切波速越高，应力波衰减越快。

Analysis of influence of source and pile-soil interaction in low strain pile integrity testing

The impact-echo method is an effective method for pile integrity testing.Based on the one dimensional (1-D) stress wave theory, the range and the extent of the changes in pile impedance can be determined from the vibration curve of reflected wave at the top of pile (including travel time, amplitude and phase).However, in practice, a pile is a cylinder rather than a rod for the induced waves, and the section deformation is not uniform.In this study, the three-dimensional wave phenomena exhibited in the wave-field near the pile top are analyzed from the components of the wave excited by the point sources and the multiple reflections from the side of the pile top.The propagation behavior of the waves in the far-field, which is far from the top, is analyzed based on the longitudinal waves in cylinders.The results show that the three-dimensional wave in the near field and the dispersive characteristics of the waves in the far field can be mitigated, and the signals measured at the top can be approximately analyzed using 1-D stress wave theory when the receiver position and source frequency content meet some conditions.Under the interaction between the pile and the soil, the stress waves in the pile decay with propagation.The effects of shear wave velocities of pile and soil on the attenuation of stress wave are analyzed.It is shown that the stress wave attenuation is not only related to the shear wave velocity ratio of the pile and soil, but also related to the absolute values of the shear wave velocity of the pile and soil.The lower the shear wave velocity of the pile is, the higher the shear wave velocity of the soil is, and the faster the stress waves decay.