基于声发射时频特征的岩石破裂前兆识别方法

Rock Fracture Precursor Identification Method Based on Acoustic Emission Time-frequency Characteristics

为得到岩石破裂的有效前兆信息,通过时频分析方法研究了白云岩破裂的声发射波形信号。对取样于2008年汶川地震引起的东河口滑坡源区的白云岩样品开展三轴多级循环加载试验,分析其力学及声发射特性,并从声发射波形时频特征分析岩石破裂前兆信息。在声发射波形参数(主频)的基础上提出一个新的特征参数:主主频(即最大主频),对13个主主频关键点进行傅里叶变换(FT)和三维短时傅里叶变换(3D-STFT),分析其时频演化特征,以期得到岩石破裂有效的前兆信息。研究结果表明:声发射事件率、累积振铃计数和能量均反映白云岩试样受力破裂过程的动态演化规律;白云岩试样的主频呈带状演化,破裂前兆表现为高频区间向低频、中频区间转移,累积主频曲线的斜率在891 s处达到峰值,可作为岩样破裂的前兆信息之一;在6次循环加、卸载中,主主频呈现高频率值与低频率值交替出现的规律,将主主频突降的第11个点(784 s)作为预警前兆之一,相比主频预警点(891 s)提前了107 s。对比分析可知主主频能获取更为细节的岩石破裂前兆信息,从而为岩石破裂预警提供科学依据和理论基础。

In order to obtain the effective precursor information of rock fracture,the acoustic emission waveform signals of dolomite fracture are studied by time-frequency analysis.A triaxial multi-stage cyclic loading test was carried out on the dolomite samples sampled from the source area of Donghekou landslide caused by Wenchuan earthquake in 2008.The mechanical and acoustic emission characteristics of the dolomite samples were analyzed,and the precursor information of rock failure was analyzed from the time-frequency characteristics of acoustic emission waveform.Based on the acoustic emission waveform parameter dominant-frequency,a new characteristic parameter:max-f_(max)(maximum dominant-frequency)was proposed.The Fourier transform(FT)and 3D short-time Fourier transform(3D-STFT)were used to analyze the time-frequency evolution characteristics of 13 key points of the dominant-frequency,in order to obtain effective precursor information of rock failure.The results show as follows.The acoustic emission event rate,cumulative ringing count and energy all reflect the dynamic evolution of the mechanical fracture process of dolomite samples.The dominant-frequency of dolomite samples evolved in bands,and the fracture precursor showed that the high frequency range shifted to the low frequency and middle frequency range.The slope of cumulative dominant frequency curve reached the peak at 891 s,which can be used as one of the precursor information of rock sample fracture.In the 6 cycles of loading and unloading,the maximum dominant-frequency showed the rule of alternating high frequency value and low frequency value,and the 11th point(784 s)of the maximum dominant-frequency sudden drop was taken as one of the early warning precursor,107 s earlier than the dominant-frequency warning point(891 s).Comparative analysis shows that the maximum dominant-frequency can obtain more detailed precursor information of rock failure,thus providing scientific basis and theoretical basis for rock failure warning.