声发射地应力测量中凯塞点的确定

DETERMINATION OF KAISER POINT IN MEASUREMENT OF GEO-STRESS WITH ACOUSTIC EMISSION

准确判断凯塞点是岩石声发射地应力测量中的重点和难点 ,目前还没有一种有效的确定方法。对砂岩声发射试验中声发射信号的重标区间 (R/S)进行了分析 ,发现lg(R/S)与时间间隔对数值具有很好的线性相关性 ,相关系数均大于 0 .97,这表明声发射信号曲线具有分形特征。研究还发现 ,不同载荷阶段声发射信号曲线的赫斯特指数 (H)可反映声发射信号强弱变化的趋势。当H >0 .5时 ,声发射信号趋于加强 ;H <0 .5时 ,声发射信号趋于减弱。根据这一规律 ,通过计算声发射信号曲线的赫斯特指数 (或分形维数 ) ,便可确定声发射试验中的凯塞点。实践证明这是一种确定凯塞点的有效方法。

It is important and difficult to determine the Kaiser point accurately in measurement of geo stress with acoustic emission (AE). The acoustic emission signals of some sandstone samples are analyzed with Rescaled Range (R/S) method. It is found that there is a good linear correlation between lg( R/S) and logistic spacings of time, and all the correlation coefficients are more than 0.97. So the conclusion can be reached that the AE signal curves are fractal. Another experiment result shows that Hurst index ( H ) of the AE signal curves in different load steps can reflect the variation tendency of signals. The AE signal will be stronger when H >0.5, and it is weaker when H <0.5. On the basis of this character of Hurst index, the Kaiser point can be determined correctly by calculating the Hurst index of AE signal curve. Application shows that this method is effective.