利用多次散射波监测介质性质变化的试验研究

 与传统的直达波检测相比，多次散射形成的尾波对介质性质变化具有很高的灵敏度。本研究建立了试验测试系统，对水泥和岩石样品开展散射波试验研究，分析尾波发育规律、尾波干涉数据处理方法和应用条件。得出岩石散射体的浓度和尺度、超声波偏振方向、频率对散射波和尾波形成具有重要影响；观测系统的高度重复性、稳定和高信噪比(SNR)尾波以及变窗口互相关扫描分析是获得高精度尾波干涉测量的关键。测试获得了水泥试件纵波、横波和尾波波速对应力变化的敏感性，与直达波相同，所有样品尾波波速都随应力的增大而增大，不同样品间增大的速率(应力敏感性)不同且随杨氏模量的增大而减小。将该方法用于水泥试件水饱和及楼房承载柱环境变化响应的监测，获得清晰的水泥试件水饱和进程，以及楼房承载柱尾波波速随环境湿度的变化，为利用多次散射波监测介质微弱变化和研究介质性质变化的精细过程创造条件。

EXPERIMENTAL STUDY OF VARIATION OF MEDIA PROPERTIES MONITORING USING MULTIPLE SCATTERING WAVES

Comparing with directly arriving waves,multiple-scattering coda waves are highly sensitive to physical properties and stress variation of medium.In this paper,a test system is established and experimental studies of scattering waves on concrete and rock samples are carried out.The coda wave formation mechanism and influence factor are analyzed.The coda wave interferometry(CWI) by cross-correlation of coda waves and the data processing method are also discussed.The formations of scattering wave and coda wave are significantly influenced by the rock scatters concentration and size,ultrasonic polarization direction and frequency.The accuracy and sensitivity of velocity changes by CWI are an order of magnitude higher than P-wave and S-wave velocities.It is crucial to this high precision technology that the repeatability and stability of measurement system,high signal-to-noise ratios of coda waveforms and cross-correlation analysis time window selection.The stress dependence of wave velocities for the concrete samples is attained.The coda wave velocities of all the samples increase with the increasing stress,which is same to directly arriving waves.The sensitivity of coda wave velocity changes decreases with the increasing of Young s modulus.In this experiment,CWI is also used for monitoring the building pillar s velocity change with environment humidity and water saturation process in a concrete sample.It is shown that CWI is a high precision monitoring means to monitor the variation of media properties.