基桩反射波法三维干扰成因与最佳采样方法研究

研究了基桩反射波法三维干扰信号的成因和消除三维干扰的最佳采样方法。通过模态叠加法,发现三维干扰主要来源于使桩顶表面产生非均匀轴向运动的轴对称径向振动模态,桩顶表面的模态位移零点即为三维干扰最小点。通过参数分析,提出了三维干扰最小点位置的函数表达式,从而修正了现有基桩检测规范推荐的采样位置。基于上述模态在桩顶面位移零点两侧位移反向的特点,提出了双速度平均法,该方法利用双通道仪的两个探头在干扰最小点两侧采样并平均以达到消除三维干扰的目的。与干扰最小点采样法相比,该方法测点选择范围更大,信号质量更优。工程实测数据和数值模拟结果证明了上述结论的正确性。

Three-dimensional interference sources and optimal sampling location of piles utilizing reflected wave method

When utilizing the reflected wave method for integrity testing of piles, signals are usually biased due to the three-dimensional (3D) wave motion of the piles. In order to reduce the signal bias, both the 3D interference sources and the optimal sampling positions are studied. By means of the mode superposition, it is observed that the interference sources are mainly from a specific kind of vibration modes, in which the top plane of a pile will deform non-uniformly in the axial direction. There exist stationary points on the top plane where the interference signal is the minimum. They are called 3D interference minimum points, the optimal positions for signal sampling. Through parameter analysis, a mathematical expression is derived for determination of the 3D interference minimum points. This expression reflects the effect of pile materials, and may be regarded as a modification of the existing code method. Based on the fact that the displacements at both sides of an interference minimum point are adverse, a double-speed average method is proposed, by measuring and averaging the signals of two corresponding points at both sides. Using this method, the sampling location can be chosen in a wide range, while the signal quality is much higher than that of the 3D interference minimum point sampling method. The accuracy of the proposed method is further checked through both the in-situ tests and the numerical simulations.