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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。
The cause of three-dimensional interference signal of pile reflection wave method and the best sampling method to eliminate three-dimensional interference are studied. Through the modal superposition method, it is found that the three-dimensional interference mainly comes from the axisymmetric radial vibration mode which causes the non-uniform axial movement of pile top surface. The zero point of modal displacement on pile top surface is the minimum point of three-dimensional interference. Through the parameter analysis, a function expression of the position of the minimum interference point of three-dimensional interference is proposed so as to correct the recommended sampling position of the existing pile detection specification. Based on the above-mentioned modal characteristics of displacement reversal at the zero point of the top of the pile, a two-speed averaging method is proposed. The method uses the two probes of the dual-channel instrument to sample and average on the two sides of the minimum interference point to eliminate the three-dimensional interference purpose. Compared with the sampling method with the least interference point, this method has a larger range of measurement points and better signal quality. The measured data and numerical simulation results show the correctness of the above conclusions.