大理岩单轴压缩破坏次声波特征的加载速率效应研究

Loading rate effects on infrasound characterization of uniaxial compression damage in marble

  • 摘要: 低频次声波信号有能量衰减小、穿透性强等特点,在岩石破裂的非接触监测上具有显著优势。为探究岩石破坏过程次声波信号特征与加载速率的关系,开展了4种加载速率下大理岩单轴压缩次声波监测试验。对采集的次声波信号进行去噪,通过快速傅里叶变换和小波包变换提取了次声波主频和能量参数,研究了大理岩破裂过程次声波主频和能量特征,着重分析了加载速率对大理岩次声波主频和能量的影响,并基于次声波最大能量提出大理岩失稳破坏前兆预警判据。研究结果表明:不同加载速率下大理岩次声波主频均呈条带状演化,主要分布在1、2、3、4、5、6 Hz共6条频带上。随加载速率的增大,主频条带由密集变稀疏,6 Hz主频条带会逐渐消失。2 Hz和4 Hz主频受加载速率效应的影响最显著,随加载速率的增大,2 Hz主频占比减小,而4 Hz主频占比增加,占主导地位的优势次声波主频由2 Hz转变为4 Hz。不同加载速率下大理岩次声波在塑性阶段均出现明显的激增现象,出现最大能量,随加载速率的增大,次声波信号最大能量和累计能量越来越小。次声波最大能量出现后进入平静期可作为大理岩失稳破坏的前兆特征,加载速率越大,次声波最大能量的位置越接近峰值应力,平静期持续时间越短。提出了基于次声波能量比的大理岩失稳破坏前兆判据,随加载速率的增大,前兆判据的临界值逐渐减小。

     

    Abstract: Low-frequency infrasound signals are distinguished by minimal energy attenuation and robust penetration capabilities, endowing them with notable advantages for non-contact monitoring of rock fracture. In order to investigate the relationship between infrasonic signal characteristics and loading rate during rock instability failure, uniaxial compression infrasonic monitoring tests were conducted on marble at four different loading rates. The gathered infrasound signals underwent denoising, and the dominant frequency as well as energy parameters of the infrasound were extracted utilizing Fast Fourier Transform and Wavelet Packet Transform. The characteristics of the dominant frequency and energy of infrasound in marble were studied, the influence of loading rate on the dominant frequency and energy of infrasound in marble was analyzed, and the precursor warning criterion of marble instability damage was proposed based on the maximum energy of infrasound. The results showed that: The dominant frequency of marble infrasonic waves exhibited distinct band-like evolution patterns under different loading rates, primarily distributed within six frequency bands: 1 Hz, 2 Hz, 3 Hz, 4 Hz, 5 Hz, and 6 Hz. With the increase of the loading rate, the main frequency strip changes from dense to sparse, and the 6 Hz main frequency strip will gradually disappear. The dominant frequencies at 2 Hz and 4 Hz were significantly influenced by the loading rate effect, there was a decrease in proportion for the dominant frequency at 2 Hz while an increase for that at 4 Hz occurred. Consequently, there was a shift in advantage dominant frequency from 2 Hz to 4 Hz. Marble infrasonic waves displayed evident surge phenomena during the plastic stage under various loading rates, and with the emergence of maximum energy. With increasing loading rates, both maximum energy and cumulative energy of infrasonic wave decreased progressively. The calm period following emergence of maximum infrasonic energy could be utilized as a precursor feature indicating marble instability and failure occurrence. With increasing loading rates, the stress level corresponding to the maximum infrasonic energy is becoming closer to the peak stress, the duration of the calm period is shorter. A precursor criterion for marble instability damage based on infrasound energy ratio is proposed, and the critical value of the precursor criterion decreases gradually with the increase of loading rate.

     

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