基桩低应变法三维干扰最小点位置的影响因素及确定方法

通过工程实测信号和数值模拟分析，证明了瞬态集中荷载敲击下，桩顶三维干扰速度信号的强度沿径向先递减后递增，存在干扰最小点，并对比了不同学者提出的干扰最小点位置处的信号。参数分析表明，三维干扰最小点的位置与桩径、桩长、荷载脉宽、桩身混凝土弹性模量、土层剪切波速及土层泊松比等桩、土参数几乎无关，但与桩身混凝土泊松比密切相关，且泊松比越大，干扰最小点的位置越靠近桩中心。给出了干扰最小点位置与桩身混凝土泊松比之间的函数表达式，可方便应用于实际工程。

Parameter analysis of three-dimensional interference minimum point and its location determination in low strain integrity testing of piles

In this study, a three-dimensional (3D) dynamical analysis is carried out for foundation piles under the action of a concentrated pulse load at the top centre by both in-situ test and numerical simulation. It is found that the amplitude of the envelope curve of velocity signal varies along the radial direction from point to point at the top plane of a pile. There exists a point where the amplitude of the envelope curve keeps the lowest, and this point is called 3D interference minimum point. The envelope amplitude decreases firstly from pile centre to this point and then increases outwards. The signals of 3D interference minimum points are compared with others in the literature. It is shown that the influence on the point location from pile-soil parameters such as pile diameter, pile length, load pulse width, elastic modulus of pile concrete, shear wave velocity and Poisson's ratio of surrounding soil, can be ignored. However, the point location is highly depending on the Poisson's ratio of pile concrete. The location of interference minimum point is more closed to the pile center when the value of Poisson's ratio of pile concrete is higher. A mathematical expression between the point location and the Poisson's ratio of pile concrete is then deduced, showing that the proposed method can be easily applied to practical engineering.