Acoustic emission features and P-wave first-motion polarity of tensile fractures in the rock
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摘要: 為深入探討巖石在張拉作用下破裂的聲發射特性，設計了一種膨脹劑擴張破裂的聲發射實驗，詳細分析了花崗巖、大理巖和紅砂巖聲發射信號的特征參數及P波初動極性。實驗結果表明：聲發射信號的累積計數和能量在三種巖石試樣宏觀開裂時均呈指數增長；花崗巖、大理巖和紅紗巖試樣聲發射信號的中心頻率分別主要集中在100 ~ 300 kHz、200 ~ 400 kHz、200 ~ 500 kHz；花崗巖低頻率事件占比最多，大理巖高頻率事件占比較多，而紅砂巖高頻事件占比最多， 三種巖樣膨脹力荷載后期低中心頻率聲發射信號增多，說明大尺度破裂增加；三種巖樣聲發射信號的RA主要集中在0~1.9之間，大理巖和紅砂巖AF值主要集中在50 ~ 100 kHz之間，花崗巖AF值主要集中在200 ~ 250 kHz之間，RA?AF的分布特性表明，實驗中巖樣主要以張拉破壞為主；通過P波初動極性分析法，獲得各巖樣聲發射信號的初動極性，結果顯示，花崗巖、大理巖和紅砂巖分別有77.82%、79.5%和87.42%的T-型破裂源，花崗巖、大理巖幾乎不產生S-型破裂源，而紅砂巖因為天然節理裂隙較多，有9.93%的S-型破裂源。RA?AF分布分析和p波初動極性分析都是統計分析法，可以定性描述巖石破裂類型。Abstract: To investigate the acoustic emission (AE) characteristics of tensile fracture in the rock, an AE experiment of granite, marble, and red sandstone using an expanding agent for fracture generation was designed. Characteristic parameters of AE signals and the P-wave first-motion polarity were analyzed in detail. Results show that the cumulative count and energy of the AE signal increase exponentially when a macroscopic failure occurs in all three kinds of rock samples. The centroid frequency of AE signals of granite, marble, and red sandstone samples mainly concentrates in the range of 100–300 kHz, 200–400 kHz, and 200–500 kHz, respectively, and the proportion of high centroid frequency events in the red sandstone test is the highest, followed by marble and granite. As the AE signal’s centroid frequency in all three kinds of rocks changed with the time of expander action, more AE signals with a low centroid frequency appeared in the late loading period, indicating the increase of large-scale fracture in the late loading period. Meanwhile, RA values of AE signals of the three rock samples mainly concentrate between 0 and 1.9. AF values of marble and red sandstone mainly concentrate between 50 kHz and 100 kHz, and AF values of granite mainly concentrate between 200 kHz and 250 kHz. Distribution characteristics of the RA?AF indicate that the tensile failure dominates the cracking process in such an experiment. The P-wave first-motion polarity analysis method was used to obtain the first-motion polarity of AE signals of each rock sample. Results showed that there are 77.82%, 79.5%, and 87.42% T-type crackles in granite, marble, and red sandstone, respectively. Moreover, granite and marble exhibit almost no S-type crackle, while red sandstone samples have 9.93% S-type crackles. Both RA?AF distribution and P-wave first-motion polarity analyses are statistical analysis methods, which can qualitatively analyze the type of rock fracture.
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圖 1 三種巖石試樣圖. (a)花崗巖；(b)大理巖；(c)紅砂巖
Figure 1. Three rock samples: (a) granite;(b) marble; (c) red sandstone
圖 2 膨脹劑擴張破裂的聲發射實驗系統示意圖
Figure 2. Schematic diagram of the rock AE experimental system for expansion fracture
圖 3 聲發射特征參數和應變隨時間變化曲線. (a)花崗巖；(b) 大理巖；(c) 紅砂巖
Figure 3. Variation curve of AE parameters and strain over time: (a) granite; (b) marble; (c) red sandstone
圖 4 三種巖石中心頻率的時域分布散點圖. (a) 花崗巖；(b) 大理巖；(c) 紅砂巖
Figure 4. Scatter diagram of the centroid frequency in the time domain of the three rock samples: (a) granite; (b) marble; (c) red sandstone
圖 5 三種巖石不同中心頻率頻段聲發射事件占比分布圖. (a) 花崗巖；(b) 大理巖；(c) 紅砂巖
Figure 5. Distribution of AE events in different centroid frequency intervals of the three stones: (a) granite; (b) marble; (c) red sandstone
圖 6 三種巖石微觀結構圖. (a)花崗巖；(b)大理巖；(c)紅砂巖
Figure 6. Microstructure of rocks in the transparent refractive index experiment: (a) granite; (b) marble; (c) red sandstone
圖 7 三種巖樣RA?AF散點圖和密度云圖. (a)，(c)，(e)分別為花崗巖、大理巖、紅砂巖RA?AF散點圖；(b)，(d)，(f)分別為花崗巖、大理巖、紅砂巖RA-AF密度云圖
Figure 7. RA?AF distribution and density cloud diagram of the three kinds rock samples: (a), (c), (e) is RA?AF scatter diagram of granite, marble and red sandstone respectively; (b), (d), (f) is density cloud diagram of granite, marble and red sandstone respectively
圖 8 三種巖石實驗中T-型、C-型和S-型破裂源聲發射事件數所占比率. (a)花崗巖；(b)大理巖；(c)紅砂巖
Figure 8. Proportion of T-type, C-type, and S-type AE events in experiments of the three rock samples: (a) granite; (b) marble; (c) red sandstone
圖 9 (a) 膨脹劑作用下巖石試樣受力示意圖；(b) T-type破裂示意圖；(c) S-type破裂示意圖；(d) C-type破裂示意圖
Figure 9. (a) Schematic diagram of the force in the rock sample under the action of the expansion agent; (b) T-type rupture; (c) S-type rupture; (d) C-type rupture
表 1 聲發射采集系統參數設置
Table 1. AE instrument parameter setups
Thres
hold /
dBSampl
ing rate /
MHzPre-tri
gger /
μsPeak defi
nition time
(PDT) /μsHit defi
nition time
(HDT) /μsHit loc
king time
(HLT) /μs40 5 256 50 200 300 
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中文字幕在线观看表 2 三種巖石宏觀破裂階段累積計數線性擬合一次項系數
Table 2. Linear fitting first-order coefficients of cumulative counts during macroscopic fracture stages of the three rock samples
Granite Marble Red sandstone 149.45 104797 20254
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