苗胜军, 尚向凡, 王辉, 梁明纯, 杨鹏锦. 近疲劳强度循环荷载下粉砂岩强度变化机制[J]. 工程科学学报, 2024, 46(6): 982-993. DOI: 10.13374/j.issn2095-9389.2023.07.31.003
引用本文: 苗胜军, 尚向凡, 王辉, 梁明纯, 杨鹏锦. 近疲劳强度循环荷载下粉砂岩强度变化机制[J]. 工程科学学报, 2024, 46(6): 982-993. DOI: 10.13374/j.issn2095-9389.2023.07.31.003
MIAO Shengjun, SHANG Xiangfan, WANG Hui, LIANG Mingchun, YANG Pengjin. Strength change mechanism of siltstone under near fatigue strength cyclic loading[J]. Chinese Journal of Engineering, 2024, 46(6): 982-993. DOI: 10.13374/j.issn2095-9389.2023.07.31.003
Citation: MIAO Shengjun, SHANG Xiangfan, WANG Hui, LIANG Mingchun, YANG Pengjin. Strength change mechanism of siltstone under near fatigue strength cyclic loading[J]. Chinese Journal of Engineering, 2024, 46(6): 982-993. DOI: 10.13374/j.issn2095-9389.2023.07.31.003

近疲劳强度循环荷载下粉砂岩强度变化机制

Strength change mechanism of siltstone under near fatigue strength cyclic loading

  • 摘要: 通过开展不同循环次数的循环加卸载转单调加载试验,结合声发射和CT扫描技术,揭示了近疲劳强度循环荷载作用下泥质石英粉砂岩的细观破裂演化规律、裂隙扩展特征与强度变化机制. 结果表明:(1)泥质石英粉砂岩的损伤应力小于疲劳强度,可称损伤应力与疲劳强度之间的应力水平为近疲劳强度. (2)随着循环次数增加,粉砂岩峰值强度先小幅下降后持续增加最终趋于稳定,当一次循环后轴向(体积)变形从压缩(膨胀)转为几乎不变时,可认为粉砂岩的强度从劣化转为强化. (3)单调加载阶段应力接近峰值强度时,粉砂岩中、低频区的声发射信号大幅增加,可将其视为岩石受压破坏的先兆. (4)当循环次数较低时,循环过程中粉砂岩的弱胶结结构断裂,有效承载面积减小,转单调加载后岩石破裂尺度增大、内部裂纹局部集中,发生劣化,呈单斜面剪切破坏. (5)当循环次数较高时,循环过程中粉砂岩胶结强度增加、细观结构更为致密与均匀,有效承载面积增大,岩石内部在泊松效应的影响下持续产生横向拉应力,转单调加载后岩石裂隙尺寸、裂隙密度和破碎程度降低,发生强化,呈张拉–剪切的复合裂隙网络.

     

    Abstract: In this paper, the microscopic fracture evolution law, crack propagation characteristics, and strength change mechanism of argillaceous quartz siltstone under near fatigue strength cyclic loading were revealed by conducting cyclic loading and unloading to monotonic loading tests with different cycles, combined with acoustic emission and CT scanning techniques. Results are summarized as follows: (1) The damage stress of argillaceous quartz siltstone is less than the fatigue strength, and the stress level between the damage stress and fatigue strength is known as near fatigue strength. (2) As the number of cycles increases, the peak strength of the siltstone first slightly decreases, then continues to increase, and finally stabilizes. When the axial (volumetric) deformation changes from compression (expansion) to almost constant after one cycle, the strength of the siltstone changes from deterioration to strengthening. (3) As the number of cycles increases, the bandwidth and density of low- and intermediate-frequency signals of argillaceous quartz siltstone gradually decrease after loading and unloading under near fatigue strength, and the high-frequency band signals become more concentrated. When the stress approaches the peak strength during the monotonic loading stage, the acoustic emission signals in the middle and low-frequency regions of the siltstone significantly increase, which can be regarded as a precursor to rock compression failure. (4) When the number of cycles is low, the siltstone fractures exhibit a weak cementation structure during cycling, and the effective bearing area decreases. After monotonic loading, the acoustic emission vibration frequency range of the siltstone is wide, with a high proportion of low- to intermediate-frequency signals. The rock-fracture scale increases, and internal cracks are locally concentrated, leading to deterioration and a single slope shear failure. (5) When the number of cycles is high, the bonding strength of the siltstone increases, the microstructure becomes dense and uniform, and the effective bearing area increases during the cycling process. Furthermore, after monotonic loading, the acoustic emission signal of the siltstone is mainly a high-frequency signal, whereas the low-frequency band signal decreases. Almost no acoustic emission signal is generated in the middle-frequency band, and the size, density, and degree of fragmentation of the rock fracture decreases. Furthermore, strengthening occurs, forming a tensile shear composite fracture network. The findings of this study can provide a basis for the long-term stability analysis and disaster warning of rock-bearing structures under cyclic loads and are of great significance for guiding the support of surrounding rock tunnels and ensuring the safe mining of coal mining.

     

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