实验研究

岩石受载破坏过程声电信号时频特征研究

刘洋1,邱黎明1,娄全2,韦梦菡1,殷山1,李鹏鹏1,程肖禾1

(1.北京科技大学 土木与资源工程学院, 北京 100083;2.河南城建学院 市政与环境工程学院, 河南 平顶山 467036)

摘要岩石受载破坏过程声电信号时域特征分析大多从声电信号幅值、振铃计数、能量等参数方面定性得出结论,并未直接给出声电信号时域相关性,且声电信号频域特征分析所用参数较单一。针对上述问题,开展了单轴压缩条件下岩石试样受载破坏过程声电信号监测实验,分析了岩石受载破坏不同阶段声电信号时频特征。结果表明:① 在压密阶段和弹性阶段,声电信号幅值基本为零;在加速破坏阶段,声电信号幅值逐渐增强,信号数量逐渐增多;在完全破坏阶段,声电信号幅值几乎同增同减,当载荷达到峰值时,声电信号幅值同时达到最大;在受载破坏全程,声发射信号幅值大于电磁辐射信号幅值。② 在加速破坏阶段,声电信号显著相关;在完全破坏阶段,声电信号高度相关;在受载破坏全程,声电信号随时间变化趋势基本相同,声电信号在时域上高度相关。③ 在加速破坏阶段和完全破坏阶段,电磁辐射信号以低频和甚低频信号为主;与电磁辐射信号相比,声发射信号频带更宽、主频幅值更大;声电信号主频集中范围相近但不完全一致;完全破坏阶段声电信号主频幅值大于加速破坏阶段声电信号主频幅值。

关键词煤岩动力灾害; 岩石受载破坏; 单轴压缩; 声发射; 电磁辐射; 时频特征; 时域相关性

0 引言

随着矿井开采深度增加,煤层赋存条件变得更复杂,煤与瓦斯突出、冲击地压等煤岩动力灾害逐渐增多,对井下作业人员和生产设备的安全造成了严重威胁,因此对煤岩动力灾害的准确监测预警尤为重要[1-2]。岩石破坏过程中,内部能量以声发射信号和电磁辐射信号等形式释放,声电信号与岩石变形破坏有直接联系[3-6],声电信号的变化与岩石破坏的各个阶段存在对应关系,因此声电信号可作为岩石破坏状态前兆信息[7-10]

邱黎明等[11]对单轴压缩过程含孔洞混凝土声电信号进行了研究,得出含孔洞混凝土破裂过程中声电信号具有一定的相关性,声电信号与所受应力之间存在正相关耦合关系。王笑然等[12]对煤岩单轴压缩破坏声电信号时域特征进行了研究,得到声电信号与加载阶段密切相关,声电信号脉冲数和能量具有较好的相关性。王岗等[13]对煤岩破裂裂纹演化过程声电信号时频特征进行了研究,得出声电信号的产生及变化随时间具有较好的一致性,且声电信号频率逐渐转向低频,主频幅值逐渐增大。夏善奎[14]对煤与瓦斯突出过程声电信号时频特征进行了研究,得到声电信号的能量和振铃计数等参数均随应力增大而增加。

前人对岩石受载破坏过程中产生的声电信号进行了大量研究,但大多从声电信号幅值、振铃计数、能量等参数方面定性分析声电信号时域特征,并未直接给出声电信号时域相关性,且声电信号频域特征分析所用参数较单一。鉴此,本文开展了岩石单轴压缩实验,同步采集岩石受载破坏全程声电信号和载荷,对声电信号相关参数进行了量化分析,研究了岩石受载破坏过程声电信号时频特征,旨在为煤岩动力灾害声电协同监测预警提供相关指导。

1 实验设计

1.1 实验系统

岩石受载破坏声电信号全波形采集系统由压力机、电磁屏蔽室、声发射传感器、电磁辐射线圈和数据采集系统组成,如图1所示。该系统可同时对声发射信号、电磁辐射信号、载荷等进行实时同步采集。电磁屏蔽室综合屏蔽效能为75 dB,可有效减少外界电磁场对实验结果的干扰;声发射传感器外接20 dB放大器;电磁辐射线圈正对试样放置,与试样平行且保持约7 cm距离,外接64 dB放大器。

1—压力机;2—电磁屏蔽室;3—声发射传感器;4—电磁辐射线圈;5—数据采集系统;6—试样。
图1 岩石受载破坏声电信号全波形采集系统
Fig.1 Full-waveform acquisition system for acoustic-electric signals of rock failure under load

1.2 试样制备

实验所用石灰岩取自陕北马家沟组,页岩取自四川长宁马龙溪组。按照国际岩石力学学会标准,进行取芯、切割,打磨制成φ25 mm×50 mm标准试样(图2),试样端面的平整度控制在±0.02 mm内。

1.3 实验方案

分别取4块石灰岩和页岩试样进行岩石单轴压缩实验,实验加载方式为位移控制,加载速率为2 μm/s,破裂百分比为20%,压力机采样频率为50 Hz。为保证实验结果的准确性,实验使用2组声发射传感器和电磁辐射线圈,声电信号采样频率为2 MHz。运用Matlab软件对实验结果进行处理,根据加载全过程声电信号的波形特征,设定声电信号门槛电压分别为0.2,0.02 V,声电信号的波形鉴别时间分别为0.2,1 ms。统计声电信号幅值、振铃计数等参数,用于对声电信号时频特征进行分析。

(a) 石灰岩

(b) 页岩

图2 岩石试样
Fig.2 Rock samples

2 实验结果及分析

2.1 声电信号时域特征

试样载荷-声电信号随时间变化曲线如图3所示。根据试样应力-应变特点,将试样受载破坏过程分为压密阶段、弹性阶段、加速破坏阶段和完全破坏阶段。从图3可看出:在压密阶段和弹性阶段,声电信号幅值基本为零,声电信号响应不明显且处于平稳状态;在加速破坏阶段,声电信号幅值逐渐增强且数量逐渐增多,其中声发射信号数量更多;在完全破坏阶段,声电信号幅值几乎同增同减,当载荷达到峰值时,声电信号幅值同时达到最大。从受载破坏全程来看,声发射信号幅值大于电磁辐射信号幅值,说明声发射信号能量更大;声电信号随时间变化趋势基本相同,说明声电信号时域相关性较好;但声电信号并不是一一对应的,这是由于声电信号产生机理并不完全相同,并且在实验过程中少部分声电信号随滤波去噪过程被剔除。

(a) 石灰岩1

(b) 页岩2

I—压密阶段;II—弹性阶段;III—加速破坏阶段;IV—完全破坏阶段。
图3 典型试样载荷-声电信号随时间变化曲线
Fig.3 Change curves of load-acoustic-electric signals with time of typical samples

为进一步分析声电信号时域相关性,采用皮尔逊法[15]计算受载破坏全程声电信号振铃计数的相关系数,见表1(由于岩石破坏主要发生在加速破坏和完全破坏阶段,本文重点对这2个阶段进行讨论)。可看出在加速破坏阶段,石灰岩、页岩试样声电信号振铃计数相关系数平均值分别为0.623和0.691,表明声电信号显著相关;在完全破坏阶段,石灰岩、页岩试样声电信号振铃计数相关系数平均值分别为0.981和0.913,表明声电信号高度相关;在受载破坏全程,石灰岩、页岩试样声电信号振铃计数相关系数平均值分别为0.963和0.869,表明声电信号高度相关。

表1 声电信号振铃计数相关系数
Table 1 Correlation coefficients of ringing count of acoustic-electric signals

岩石破坏阶段石灰岩1石灰岩2石灰岩3石灰岩4石灰岩平均值页岩1页岩2页岩3页岩4页岩平均值加速破坏阶段0.6380.6120.6160.6250.6230.6900.6210.7780.6740.691完全破坏阶段0.9790.9970.9900.9560.9810.9320.8760.9160.9270.913受载破坏全程0.9490.9940.9870.9220.9630.8820.8550.8910.8470.869

从声电信号产生机理来看,岩石单轴压缩过程就是岩石内部裂纹萌生并扩展的过程,裂纹两端面不断分离,在此期间,端面的振动过程产生了声发射信号,端面的电荷分离过程产生了电磁辐射信号。因此实验结果表现为声电信号振铃计数相关系数较高,声电信号在时域上高度相关。

2.2 声电信号频域特征

采用快速傅里叶变换将声电信号从时域转换到频域,其中加速破坏和完全破坏阶段声电信号频谱如图4和图5所示。从信号频带来看,声发射信号频带为0~400 kHz,石灰岩、页岩试样电磁辐射信号频带分别为0~100 kHz和0~40 kHz,声发射信号频带比电磁辐射信号频带更宽,岩石破坏过程的电磁辐射信号以低频和甚低频信号为主;从信号主频集中范围来看,声发射信号主频集中在0~15 kHz和40~60 kHz,电磁辐射信号主频集中在0~10 kHz和50~60 kHz,声电信号主频集中范围相近但不完全一致,这是由于声电信号产生机理并不完全相同;从主频幅值来看,声发射信号主频幅值大于电磁辐射信号主频幅值,完全破坏阶段声电信号主频幅值大于加速破坏阶段声电信号主频幅值。

(a) 加速破坏阶段声发射信号

(b) 加速破坏阶段电磁辐射信号

(c) 完全破坏阶段声发射信号

(d) 完全破坏阶段电磁辐射信号

图4 石灰岩1声电信号频谱
Fig.4 Spectrum of acoustic-electric signals of limestone 1

(a) 加速破坏阶段声发射信号

(b) 加速破坏阶段电磁辐射信号

(c) 完全破坏阶段声发射信号

(d) 完全破坏阶段电磁辐射信号

图5 页岩2声电信号频谱
Fig.5 Spectrum of acoustic-electric signals of shale 2

从能量角度分析,完全破坏阶段岩石试样释放的能量大于加速破坏阶段,能量越大,试样对外释放的声电信号越多,导致声电信号主频幅值越高;在相同阶段中,声发射信号能量大于电磁辐射信号,因此声发射信号主频幅值更高。此外,电磁辐射线圈灵敏度不及声发射传感器,这也会对声电信号频带、主频等频域特征结果产生一定影响。

3 结论

(1) 岩石受载破坏过程依次经历了压密阶段、弹性阶段、加速破坏阶段和完全破坏阶段,声电信号时域特征表现为:在压密阶段和弹性阶段,声电信号幅值基本为零;在加速破坏阶段,声电信号幅值逐渐增强,信号数量逐渐增多;在完全破坏阶段,声电信号几乎同增同减,当载荷达到峰值时,声电信号幅值同时达到最大;在受载破坏全程,声发射信号幅值大于电磁辐射信号幅值。

(2) 在加速破坏阶段,声电信号显著相关;在完全破坏阶段,声电信号高度相关;在受载破坏全程,声电信号随时间变化趋势基本相同,声电信号在时域上高度相关。

(3) 在加速破坏阶段和完全破坏阶段,声电信号频域特征表现为:声发射信号频带比电磁辐射信号频带更宽,且岩石破坏过程的电磁辐射信号以低频和甚低频信号为主;声发射信号主频集中在0~15 kHz和40~60 kHz,电磁辐射信号主频集中在0~10 kHz和50~60 kHz,声电信号主频集中范围相近但不完全一致;声发射信号主频幅值大于电磁辐射信号主频幅值,完全破坏阶段声电信号主频幅值大于加速破坏阶段声电信号主频幅值。

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Research on time-frequency characteristics of acoustic-electric signals in process of rock failure under load

LIU Yang1, QIU Liming1, LOU Quan2, WEI Menghan1,YIN Shan1, LI Pengpeng1, CHENG Xiaohe1

(1.School of Civil and Resource Engineering, University of Science and Technology Beijing, Beijing 100083, China; 2.School of Municipal and Environmental Engineering, Henan University of Urban Construction, Pingdingshan 467036, China)

Abstract:The analysis of time-domain characteristics of acoustic emission (AE) and electromagnetic radiation (EMR) signals in process of rock failure under load mostly draws qualitative conclusions from amplitude, ringing count, energy and other parameters, without directly giving time-domain correlation of AE and EMR signals, and parameters used in frequency-domain characteristics analysis of AE and EMR signals are relatively simple. In view of the above problems, monitoring experiment of AE and EMR signals of rock samples under uniaxial compression was carried out, and time-frequency characteristics of AE and EMR signals in different stages of rock failure under load were analyzed. The results show that: ① In compressionstage and elastic stage, amplitude of AE and EMR signals is basically zero. In accelerated failure stage, amplitude of AE and EMR signals increases gradually and the number of signals increases gradually. In stage of complete failure, amplitude of AE and EMR signals increases and decreases almost at the same time. When load reaches the peak value, amplitude of AE and EMR signals reaches the maximum at the same time. Amplitude of AE signal is larger than that of EMR signal in the whole process of failure under load. ② In accelerated failure stage, AE and EMR signals are significantly correlated. In stage of complete destruction, AE and EMR signals are highly correlated. In the whole process of failure underload, variation trend of AE and EMR signals with time is basically the same, and AE and EMR signals are highly correlated in time-domain. ③ In accelerated failure stage and complete failure stage, EMR signals are mainly low frequency and very low frequency signals. Compared with EMR signal, AE signal has wider frequency band and larger amplitude of main frequency. Main frequency concentration range of AE and EMR signals is similar but not completely consistent. Amplitude of main frequency of AE and EMR signals in complete failure stage is larger than that in accelerated failure stage.

Key words:coal-rock dynamic disaster; rock failure under load; uniaxial compression; acoustic emission; electromagnetic radiation; time-frequency characteristics; time-domain correlation

中图分类号:TD315

文献标志码:A

文章编号1671-251X(2020)06-0087-05

DOI:10.13272/j.issn.1671-251x.2019120045

收稿日期:2019-12-17;修回日期:2020-06-09;责任编辑:盛男。

基金项目:国家自然科学基金资助项目(51774023,51634001);中国博士后科学基金面上资助项目(2018M641201);中央高校基本科研业务费专项资金资助项目(FRF-TP-18-081A1)。

作者简介:刘洋(1996-),男,吉林长春人,硕士研究生,研究方向为煤岩动力灾害监测预警,E-mail:18810571557@163.com。

引用格式:刘洋,邱黎明,娄全,等.岩石受载破坏过程声电信号时频特征研究[J].工矿自动化,2020,46(6):87-91.

LIU Yang,QIU Liming,LOU Quan,et al.Researchon time-frequency characteristics of acoustic-electric signalsin process of rock failure under load[J].Industry and Mine Automation,2020,46(6):87-91.