小应力扰动下岩石弹性波速变化的波形检测

Waveform detection of elastic wave velocity changes in rock under small stress perturbations

弹性波速变化能够反映岩石内部结构和应力的变化,成为工程结构监测的重要基础,其关键是实现小应力扰动下的高精度检测。在室内建立一套试验测量系统,对3类岩石的6块样品进行单轴压缩试验,同步记录小应力作用下岩石的应变、声发射及超声波波形。分析岩石非均质引起的多次散射波(尾波)特性,利用尾波干涉测量实现波速变化的高精度波形检测,发展小应力扰动下岩石弹性波速变化的检测方法,并对尾波波速随应力的变化规律进行分析。结果表明:尾波干涉测量可以实现小应力扰动下的高精度动态监测,具有对岩体扰动小、灵敏度高、稳定性好、操作简单的优点;所提方法应用的条件是介质散射强度高,尾波较为发育,观测系统重复性好;尾波波速随应力的相对变化率dv/v是岩石损伤状态的一种表征,尾波波速变化具有记忆效应;与声发射相比,所提方法稳定,易识别,可用于岩心地应力测试。

Elastic wave velocity changes can reflect changes of the rock internal structure and stress, and it becomes an important basis for monitoring engineering structures. Its key is to achieve high precision detection under the small stress perturbations. An integrated observing system was established, and six samples were measured in uniaxial compression experiment. At the same time, observational data for each system was recorded under the small stress perturbations. These data include the strain, acoustic emission and ultrasonic waveforms of the rocks. The characteristics of multiple scattering waves （coda） caused by rock heterogeneity were analyzed. Using the coda wave interferometry（ CWI）, high accuracy waveform detection of the ve- locity variation was achieved. The detection method of rock elastic wave velocity changes under small stress perturbations was developed. The regularity of wave velocity variation with stress was analyzed. The following are the conclusions ： Coda wave interferometry can achieve high-precision dynamic monitoring under the small stress perturbations. Its advantages include rock disturbance, high sensitivity, good stability and simple operation. The applieating conditions of the method include medium high scattering intensity, more developmental coda, and good repeatability of the observing system. The relative change of coda wave velocity is a kind of characterization showing the rock damage state. Coda wave velocity changes have the memory effect. Compared with the traditional acoustic emission method, the method is stable and easily identifiable. It can be used for in-situ stress test of rock.