细砂岩声发射全波形特征及频谱分析

针对细砂岩在不同应力下的破坏模式和裂纹扩展规律等问题,采用单轴压缩、定角压剪和巴西劈裂的方式对细砂岩进行加载试验,采集各试样加载过程的声发射全波形,并基于小波阈值去噪方法对原始波形去噪处理后,再采用快速傅里叶变换获得信号的频谱特征。通过分析声发射全波形及主频、次主频的演化规律,将信号频率细分为低(10,70) kHz)、中(70,120) kHz)、高(120,180) kHz)3个等级,揭示了岩石的破裂失稳过程。研究结果表明:不同试验方法下的声发射全波形差异较大,波形幅值的变化与岩石损伤的渐进过程密切相关;同等试验方法下的声发射主频、次主频具有自相似性,演化规律较一致,次主频对裂隙发育状态更敏感;低频信号反映了细砂岩破坏时的一种固有属性,与加载方式和试验方法无关,仅中频率信号和高频率的信号对应剪切滑移过程与剪切破坏模式。

Full-waveform Characteristics and Frequency Spectrum of Acoustic Emission for Fine Sandstone

To reveal the failure mode and crack propagation law of rock under different stresses, we carried out loading tests under different loading paths on fine sandstone using uniaxial compression, fixed-angle compression shear, and Brazilian splitting methods. We collected the acoustic emission(AE) full-waveform of the samples in the whole loading process and denoised the original waveform by using the wavelet threshold denoising method. Through fast Fourier transform, we obtained the frequency spectrum characteristics of the signals. By analyzing the temporal and spatial evolution of the full-waveform, dominant frequency (DF), and secondary dominant frequency (SDF), we subdivided the signal frequency into three levels, namely, low frequency (10-70 kHz), intermediate frequency (70-120 kHz), and high frequency (120-180 kHz), and revealed the process of rock failure and instability. The results indicated that the full-waveform of AE varied greatly under different loading methods. The change of amplitude was closely related to the gradual process of rock damage. Under equivalent loading method, the DF and SDF of AE are of self-similarity and their evolution law are relatively consistent. The SDF was more sensitive to the fracture development state. The low frequency signals reflected an inherent property of fine sandstone failure, irrelevant to the loading methods and test methods. Only the intermediate frequency and the high frequency of AE signals corresponded to the shear slip process and shear failure mode respectively.