基于临界慢化理论的细砂岩破坏前兆试验研究

Experimental study on failure precursors of fine sandstone based on critical slowing down theory

为探究单轴荷载作用下含预制裂隙细砂岩的临界慢化特征与失稳前兆,利用MTS加载系统对不同预制裂隙角度的细砂岩开展单轴加载和同步声发射(Acoustic Emission,AE)探测试验,基于临界慢化理论方法对岩石试验损伤破坏过程的声发射特征参数(RA/AF、持续时间、上升时间)进行系统分析,研究结果表明:(1)在单轴加载条件下,当含预制裂隙的细砂岩石从损伤破裂相态转向失稳破坏相态时,会出现分散涨落现象,即呈现明显的临界慢化现象,表现为方差和自相关系数的骤然增大。(2)窗口长度和滞后步长对方差的前兆特征出现时间没有明显影响,而对自相关系数的波动性有较大影响,当窗口长度和滞后步长较小时,自相关系数波动较大;当窗口长度和滞后步长较大时,自相关系数波动较小。(3)声发射RA/AF值、持续时间、上升时间的方差和自相关系数前兆信号突变时间相同,波形起伏相似,且出现在新的微裂纹萌生的不可逆塑性变形阶段,故声发射RA/AF、持续时间、上升时间的方差和自相关系数增大可作为失稳前兆特征信息。(4)自相关系数相比方差而言波动较大,因此可将方差作为岩石损伤破坏向失稳破坏转变的主要判据,自相关系数作为辅助判据。研究成果可对滑坡、崩塌、采矿、隧道等突发性强、外部变形不明显的岩质脆性破坏的短临监测预警提供重要参考。

In order to explore the critical slowdown characteristics and instability precursors of fine sandstone with prefabricated fractures under uniaxial loading,uniaxial loading and synchronous acoustic emission(AE) were carried out on fine sandstone samples with different prefabricated fracture angles using MTS loading system,and the acoustic emission characteristic parameters(RA/AF value,duration and rising time) in the damage and failure processes of rock were systematically analyzed based on the critical slowing down theory method. The results indicated that, under uniaxial loading,there will be a dispersion fluctuation phenomenon when the fine sandstone with prefabricated cracks changes from fracture damage to instability failure,that is,an obvious critical slowing down phenomenon,which is manifested by the sudden increase of the variance and the autocorrelation coefficient.The window length and the lag step have no significant effect on the precursory characteristics of the variance,but have a great influence on the volatility of the autocorrelation coefficient. When the window length and the lag step are small,the autocorrelation coefficient fluctuates greatly. When the window length and the lag step length are large,the autocorrelation coefficient fluctuates less. The variances of RA/AF value,duration and rising time are the same as the mutation time of autocorrelation coefficient precursor signals,and the waveform fluctuations are also similar,which appears in the irreversible plastic deformation stage of new microcrack initiation. Therefore,the variances of RA/AF value,duration and rising time,and the increase of the autocorrelation coefficient of AE can be used as the precursor characteristics of instability. The autocorrelation coefficient fluctuates greatly compared with the variance. Therefore,the variance can be used as the main criterion for rock damage to instability,and the autocorrelation coefficient can be used as the auxiliary criterion. In summary,the research results can provide important reference for the short-term monitoring and early warning of rock brittle failure with sudden strong and weak external deformation such as landslide,collapse,mining and tunnel.