张拉作用下岩石破裂的声发射特性及P波初动极性

Acoustic emission features and P-wave first-motion polarity of tensile fractures in the rock

  • 摘要: 为深入探讨岩石在张拉作用下破裂的声发射特性,设计了一种膨胀剂扩张破裂的声发射实验,详细分析了花岗岩、大理岩和红砂岩声发射信号的特征参数及P波初动极性。实验结果表明:声发射信号的累积计数和能量在三种岩石试样宏观开裂时均呈指数增长;花岗岩、大理岩和红纱岩试样声发射信号的中心频率分别主要集中在100 ~ 300 kHz、200 ~ 400 kHz、200 ~ 500 kHz;花岗岩低频率事件占比最多,大理岩高频率事件占比较多,而红砂岩高频事件占比最多, 三种岩样膨胀力荷载后期低中心频率声发射信号增多,说明大尺度破裂增加;三种岩样声发射信号的RA主要集中在0~1.9之间,大理岩和红砂岩AF值主要集中在50 ~ 100 kHz之间,花岗岩AF值主要集中在200 ~ 250 kHz之间,RA−AF的分布特性表明,实验中岩样主要以张拉破坏为主;通过P波初动极性分析法,获得各岩样声发射信号的初动极性,结果显示,花岗岩、大理岩和红砂岩分别有77.82%、79.5%和87.42%的T-型破裂源,花岗岩、大理岩几乎不产生S-型破裂源,而红砂岩因为天然节理裂隙较多,有9.93%的S-型破裂源。RA−AF分布分析和p波初动极性分析都是统计分析法,可以定性描述岩石破裂类型。

     

    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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