声波透射法测桩波形畸变系数计算与分析

Calculation and Analysis of Waveform Distortion Coefficient of Pile by Cross-Hole Sonic Logging

声波透射法主要采用声学参数和波形畸变程度来判断基桩完整性,但是波形畸变系数无法定量计算,难以精确判定其畸变程度。通过频率域测点能量统计法计算波形畸变系数及畸变系数临界值,使用频谱及小波包分析技术探讨了完整波形和畸变波形(桩底沉渣测点、低强度不密实测点、断桩测点)的特征,并基于3层小波包分解信号的频带能量构造特征向量。结果表明:桩底沉渣测点的谱函数呈台阶状,断桩测点频谱能量主要分布在低频部分;完整测点的特征向量值最大,断桩测点的特征向量值最小,低强度不密实测点的特征向量值具有1个上凸拐点。

Cross-hole sonic logging has been widely used in the detection of the integrity of bored pile,which use the acoustic parameters(velocity,wave amplitude,product of the slope of two adjacent lines on the time-depth curve and acoustic time difference(PSD)and the extent of waveform distortion to determine the classification of pile integrity,but the extent of waveform distortion can not be expressed quantitatively.The waveform distortion coefficient and the critical value of distortion coefficient is calculated by the point energy statistics method in frequency domain,using the spectrum analysis and wavelet packet analysis method to explore the features of normal waveform and distortion waveform(the measuring point of pile with bottom sediment,low intensity and non dense pile,broken pile),and the feature vector is structured via the frequency band energy of 3 layer wavelet packet decomposition signal.The results show that the spectrum function for the measuring point on the pile with bottom sediment is stepped,the spectrum energy for the measuring point on broken pile is mainly distributed in the low frequency part;and the eigenvector of the normal measuring points is the largest;the broken pile is the smallest;the non-dense measuring points with low intensity have 1 upper convex point.