单轴压缩下正交型交叉裂隙砂岩的破坏前兆试验研究

Test study on failure precursors of orthogonal cross fractured sandstone under uniaxial compression

为探究单轴压缩下正交型交叉裂隙砂岩的破坏前兆信息,开展正交型交叉裂隙砂岩的单轴压缩声发射试验,分别从声发射振铃计数率的临界慢化特征、主频与平均频率质心的演化、小波包能谱特征三个角度进行研究。研究发现试样加载至临近峰值应力时均表现出明显的临界特征:声发射振铃计数率呈“双峰特征”、累积振铃计数急剧攀升;振铃计数率的自相关系数上升到较高的值发生大幅度波动、方差发生量级式“增加-降低-增加”的变化;低频声发射信号数量明显增加,平均频率质心则表现为“先增后减”式变化;对声发射波形信号进行4层小波包分解,3^(#)~16^(#)频带能量占比呈“明显下降-波动式上升”式变化;三种破坏前兆识别方法所得到的前兆响应系数(precursor response coefficient,PRC)的大小顺序依次为:临界慢化特征>频域特征>小波能谱特征,前兆响应应力(precursor response stress,PRSR)的大小顺序与前者相反;随着主裂隙与轴向应力之间夹角的增大;随着主裂隙与轴向应力夹角的增大,三种破裂前兆识别方法所识别前兆点出现时间均延迟。

Here,to explore failure precursor information of orthogonal cross fractured sandstone under uniaxial compression,uniaxial compression acoustic emission tests were conducted for orthogonal cross fractured sandstone.The study was performed from 3 perspectives of critical slowing characteristics of acoustic emission ringing count rate,evolutions of main frequency centroid and average frequency centroid and characteristics of wavelet packet energy spectrum.Study showed that when specimens are loaded near peak stress,they have obvious critical characteristics of acoustic emission ringing count rate exhibiting a"double-peak feature"and cumulative ringing counting increasing sharply;autocorrelation coefficient of ringing count rate ascends to a higher value and then fluctuates significantly,its variance undergoes a pattern of"increase-decrease-increase";low-frequency acoustic emission signal amount obviously increases while average frequency centroid has a"firstly increase and then decrease"pattern;4-layer wavelet packet decomposition is performed for acoustic emission waveform signals,the energy proportion of 3^(#)-16^(#)frequency bands has an"obvious decrease-fluctuation increase"pattern;the magnitude order of precursor response coefficients(PRC)obtained with 3 methods to identify failure precursors is of critical slowing feature>frequency domain feature>wavelet energy spectrum feature,and the magnitude order of precursor response stress(PRSR)is opposite to the former;with increase in angle between main fracture and axial stress,occurrence time of precursor points identified with the 3 fracture precursor identification methods is delayed.