不同围压下岩石声发射不可逆性及其主破裂前特征信息试验研究

 通过对花岗岩在不同围压下循环加卸载声发射(AE)试验，得到岩石加卸载损伤破坏过程中高、低频通道中AE累计振铃计数、岩石应力与时间的关系。基于此，研究岩石AE的不可逆性特征。同时运用快速傅里叶变换FFT逆变换对Kaiser点AE信号进行消噪，并通过FFT分析消噪后信号的频谱特征，探求岩石主破裂前特征信息。研究结果表明：(1) 两通道中接收到的AE振铃计数整体变化趋势基本相同，所揭示的Kaiser效应和Felicity效应规律基本一致；两通道中AE振铃计数特征主要区别在于数量不同；(2) Kaiser点主频分布在46.39～70.80与151.37～166.99 kHz范围内。岩石主破裂前，随轴向应力水平增加，低频通道中Kaiser点主频整体变化趋势由较低频向较高频转移，高频通道中由较高频向较低频转移；(3) 花岗岩Kaiser效应应力上限值为极限强度的65%左右。Kaiser点的主频特征及变化规律，可为岩石的损伤破坏评价提供依据。

Experimental study of characteristics of irreversibility and fracture precursors of acoustic emission in rock under different confining pressures

Laboratory experiments on the characteristics of acoustic emission(AE) in high and low frequency channels of granite specimens under different confining pressures of cyclic loading and unloading were carried out. The relationships of the time with stress and AE cumulative counts were analyzed. On the basis，the characteristics of AE irreversibility in rock were studied. Then inverse fast Fourier transform(IFFT) was used to denoise the AE signals at Kaiser points and the characteristics of spectrums of denoised signals were analyzed with fast Fourier transform(FFT). The characteristics before the major fracturing in rock were studied. The basic characteristics of AE counts，the Kaiser effect(KE) and the felicity effect(FE) are similar in two frequency channels. The main difference between the characteristics of cumulated AE counts in two frequency channels is the quantity. The dominant frequencies at Kaiser points mainly distribute in the range of 46.39–70.80 and 151.37–166.99 kHz. With the increasing of axial stress level，the dominant frequencies at Kaiser points shift from the lower frequencies to the higher ones in the low frequency channel and shift from the higher frequencies to lower ones in the high frequency channel before the major fracturing in rock. The upper limit of KE of the granite is about 65% of the ultimate compressive strength. The results of the dominant frequencies at Kaiser points provide evidence for the damage and failure of rock.