Acoustic emission and micro-rupture characteristics of rocks under Brazilian splitting load
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摘要: 通過開展花崗巖和大理巖巴西圓盤聲發射試驗，結合掃描電鏡進行破裂面微觀形貌分析，探討了劈裂荷載下巖石聲發射特性與微觀破裂機制的關系。結果表明：基于RA（上升時間與幅值的比值）和AF（平均頻率）的變化趨勢，不同裂紋模式（拉伸裂紋、剪切裂紋以及復合裂紋）的分布和破壞強度受巖石結構影響，但巖石裂紋演化過程不受其影響。相應地，兩種巖樣破裂信號均以400～499 kHz為主，100～199 kHz的信號次之，但不同破裂階段的峰值頻率變化趨勢顯著不同。在微觀形貌上，花崗巖劈裂面的微觀形貌以層疊狀、臺階狀及平坦狀為主；而大理巖以光滑多面體狀為主。此外，結合頻率?尺度縮放關系可推測，400～499 kHz的信號應主要來自鉀長石、大理巖礦物顆粒內部的破裂；100～199 kHz的信號應主要來自石英礦物顆粒內部不連續分離以及壓密階段礦物顆粒之間的滑移。Abstract: Considering the polycrystalline and anisotropic features of rock, its mechanical failure actually involves the generation, propagation, and penetration of internal micro-cracks until an ultimate macro-fracture is achieved. The nucleation and propagation of cracks emits energy outward as elastic waves referred to as acoustic emission (AE). The close relationship between AE signals and the rock fracture mechanism has been demonstrated. Many instability and failure processes in underground engineering are induced by the effects of tensile stress on tunnels and chambers or local damage to the rock structure. Several compression experiments show that the main fracture mode of rock is tensile failure. Thus, investigations of rock AE characteristics under tensile failure and the effects of the rock fabric on crack propagation patterns are of great significance. This study assesses the signal characteristics AE and its relationship with the micro-rupture mechanisms in granite and marble under tensile stress. Herein, an MTS-322 rock mechanical test system was employed to carry out Brazilian split tests, and a scanning electron microscope was employed to carry out micro-morphological analysis of rupture surfaces. According to the trends of RA and AF, the distribution of crack modes-tensile and shear or mixed patterns in both rock types and its fracture strength depend on the rock fabric. By contrast, the evolution process of crack propagation appears to depend on the softening process. Although the rock fracture signals are mainly in the range of 400?499 kHz and 100?199 kHz, the variation trend of peak frequency shows significant differences at different failure stages. At the microtopographic level, granite mainly shows three micro-morphologies, including laminated, stepwise, and smooth planar patterns. Marble is mostly smooth polyhedrals. The signals at 400?499 kHz may be inferred to be mainly generated by fractures in the k-feldspar and marble minerals, while those at 100?199 kHz are mainly produced by discontinuous separation among quartz mineral particles and slipping among mineral particles in the compaction stage.
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圖 1 兩種巖石微觀結構圖. （a）花崗巖; （b）大理巖
Qtz—石英; Kfs—鉀長石; Dol—白云石; Bt—黑云母; PI—斜長石; Cal—方解石
Figure 1. Micro-structures of rock samples in the transparent refractive index experiment: (a) granite; (b) marble
圖 3 巴西劈裂實驗中兩種巖石的破壞形態. （a）花崗巖; （b）大理巖
Figure 3. Failure form of granite and marble in the Brazilian split test: (a) granite; (b) marble
圖 5 劈裂荷載下巖石聲發射信號RA值與AF值的關系分布圖. （a）花崗巖RA值與AF值分布圖; （b）花崗巖RA值與AF值數據密度云圖; （c）大理巖RA值與AF值分布圖; （d）大理巖RA值與AF值數據密度云圖
Figure 5. RA and average frequency distribution diagrams of granite and marble under a splitting load: (a) RA versus AF distribution diagram in granite; (b) RA versus AF data density map in granite; (c) RA versus AF distribution diagram in marble; (d) RA versus AF data density map in marble
圖 6 兩種巖石的峰值頻率隨加載時間的變化. （a）花崗巖; （b）大理巖; （c）花崗巖峰值頻率隨時間變化的密度云圖; （d）大理巖峰值頻率隨時間變化的密度云圖
Figure 6. Temporal peak frequency distribution under different splitting loads: (a) granite and (b) marble; (c) peak frequency versus time data density maps in granite; (d) peak frequency versus time data density maps in marble
圖 7 不同應力水平下的峰值頻率變化. （a）花崗巖; （b）大理巖
Figure 7. AE peak frequencies at different stress levels: (a) granite; (b) marble
圖 8 花崗巖劈裂面電鏡掃描形貌圖. （a）石英顆粒層平坦狀形貌圖; （b）鉀長石臺階狀形貌圖; （c）鉀長石顆粒疊狀形貌圖; （d）石英顆粒能譜圖; （e）臺階狀鉀長石顆粒能譜圖; （f）層疊狀鉀長石顆粒能譜圖
Figure 8. SEM images of the splitting surfaces of granite: (a) “smooth planar” morphology of quartz; (b) “sidestep” morphology of k-feldspar; (c) “stack-up” morphology of k-feldspar; (d) energy spectrum diagram of quartz; (e) energy spectrum diagram of “sidestep” morphology of k-feldspar; (f) energy spectrum diagram of “stack-up” morphology of k-feldspar
圖 9 大理巖劈裂面電鏡掃描形貌圖. （a）白云石顆粒光滑多面體狀形貌圖; （b）方解石聚片雙晶結構形貌圖; （c）圖（a）黑圈區域高分辨率下的形貌圖; （d）白云石顆粒能譜圖; （e）方解石顆粒能譜圖
Figure 9. SEM photos of the fracture surfaces of marble in the Brazilian split test: (a) “smooth polyhedrals” morphology of dolomite; (b) “polycrystalline” morphology of calcite; (c) high-magnification morphology of the black square in (a); (d) energy spectrum diagram of dolomite; (e) energy spectrum diagram of calcite
表 1 巖樣基本參數
Table 1. Basic parameters of the rock samples
試樣編號 直徑/mm 高/mm 密度/(g·cm?3) 波速/(m·s?1) G1 48.41 49.95 2.61 4197.83 G2 48.57 50.36 2.63 4272.61 G3 48.33 50.62 2.62 4211.35 M1 50.99 49.32 2.85 3825.41 M2 50.35 48.19 2.78 3901.74 M3 50.79 48.57 2.85 3857.66 
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表 2 聲發射設備參數設置
Table 2. Parameter settings of the acoustic emission device
門檻值/
dB前置增益/
dB采樣長度/
kb采樣頻率/
MHzPDT/
μsHLT/
μsHDT/
μs40 40 5 10 50 300 200
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表 3 不同巖石聲發射RA-AF分布差異
Table 3. Differences in RA-AF distribution obtained from Fig. 5
巖石類型 編號 RA值/(ms·V?1) AF值/kHz 花崗巖 G1 0～1.36 75～184 G2 0～1.22 80～177 G3 0～1.13 82～186 平均值 0～1.24 79～182 大理巖 M1 0～0.52 100～174 M2 0～0.71 93～167 M3 0～0.86 97～185 平均值 0～0.70 97～175
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中文字幕在线观看表 4 巴西劈裂荷載下巖石聲發射峰值頻率分布
Table 4. Distribution percentages of AE peak frequency for four rock types in the Brazilian split test
試樣編號 峰值頻率占比/% <100 kHz 100～199 kHz 200～299 kHz 300～399 kHz ≥400 kHz G1 5.92 29.33 6.84 8.04 49.86 G2 4.85 14.15 4.18 6.24 70.58 G3 4.35 19.92 7.83 8.41 59.50 平均值 5.04 21.13 6.28 7.56 59.98 M1 7.19 26.87 11.35 3.56 51.03 M2 15.64 32.21 0.88 1.75 49.52 M3 6.97 20.40 0.01 2.40 60.21 平均值 9.93 26.49 7.41 2.57 53.58
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