岩石临破裂前波速变化特征的实验研究

Experimental study of velocity characteristic before rock fracture

为了提高波速的测量精度以便能观测到岩石临破裂前波速的微小变化,采用了波形的数值化,波的叠加,波的互相关和DTE(Subsample delay time estimate)方法和cosine插值,使时间分辨率提高到0.001μs,波速分辨率达到1m/s.在较小的应力增量(0.17MPa)下测量了波的延迟时间,进而得到速度随应力的变化规律.实验结果显示在0.98破裂强度时岩石波速最大,然后下降直到破裂,此期间的波速下降量约30m/s.同时对临破裂前波的主频能量进行了计算,其变化规律与波速相同,认为破裂前的有关变化与岩石膨胀有关.最后用涨落模型讨论了延迟时间的方差变化.

In order to measure the small change of velocity before rock fracture,the velocity measurement precision must be improved,the methods including digital wave form,the wave stacking,cross correlation and Subsample delay time estimate were used,the precision of time and velocity reached to 0.001 micro second and 1 m/s respectively.The delay time was measured as the stress increase with the interval of 0.17 MPa,then the rule of velocity as stress increase was obtained.Experimental results showed the velocity had the maximum value at the rock strength of 0.98,after that the velocity decreased about 30m/s to fracture.The power of wave at main frequency was calculated and had the same characteristic with velocity,it was considered the changes may be caused by rock dilation.The square error of delay time was discussed by using the fluctuation model.