为研究多级等幅循环荷载下应力幅值对红砂岩力学行为和断裂模式的影响,通过MTS-816岩石力学试验机和声发射监测技术,分析了循环荷载过程中红砂岩的强度和变形行为,总结了不同应力幅值下声发射参数的演化规律以及试样最终破坏模式。结果表明:较低的应力幅值对砂岩试样有强化作用,而高应力幅值下砂岩的损伤劣化则较为严重;应力幅值的增大对砂岩有硬化作用,循环荷载下红砂岩的刚度和弹性应变能整体上有所提高;在单个疲劳阶段中,声发射信号随循环次数的增加逐渐由活跃趋于稳定;在较大应力幅值下,试样破坏时的声发射振铃计数更加活跃,对应声发射累计曲线中的突增现象更明显;随着应力幅值的增大,试样破坏时的裂纹贯通和岩块脱落现象更显著。研究成果有助于揭示循环荷载对致密红砂岩力学特性和断裂行为的影响机理。

[Objective] During tunnel excavation, mining roadway development, or other underground construction processes, the rock mass of underground engineering is typically subjected to multi-stage permanent dynamic and repetitive stress disturbances. Moreover, cyclic stress amplitude is recognized as one of the primary factors influencing the occurrence of dynamic disasters in underground engineering. This study aims to investigate the influence of stress amplitude on the mechanical behavior and fracture modes of red sandstone under multi-stage constant-amplitude cyclic loading. [Methods] Utilizing an MTS-816 rock mechanics servo-testing system and real-time acoustic emission (AE) monitoring technology, the strength and deformation behaviors of red sandstone specimens during multi-stage cyclic loading were analyzed in detail. The evolution patterns of AE parameters under varying cyclic stress amplitudes and the final failure modes of the red sandstone specimens were elucidated. [Results] Lower cyclic stress amplitudes were found to impart a certain strengthening effect on red sandstone specimens, whereas higher stress amplitudes induced more severe deterioration. The increase in cyclic stress amplitude exhibited a hardening effect on the sandstone. Under multi-stage constant-amplitude cyclic loading, the elastic modulus and elastic strain energy of the red sandstone specimens were generally enhanced. Within a single fatigue loading stage, the AE signals gradually transitioned from active to stable with the increase in loading cycles. Under lower stress amplitude conditions, the red sandstone specimens exhibited a higher number of AE ring-count events during the loading process, and the cumulative AE curve showed only a sudden increase at the moment of failure. In contrast, for specimens under higher stress amplitudes, the AE activity remained relatively stable in the early loading stage but became more intense at the time of failure. An increase in stress amplitude led to the formation of larger axial primary cracks at specimen failure, and the secondary cracks and local spalling phenomena caused by crack coalescence became more severe. Specimens under high stress amplitudes were more prone to splitting failure dominated by overall tensile cracks. [Conclusion] The cyclic stress amplitude has a significant impact on the safety and stability of underground engineering. Therefore, the dynamic cyclic stress amplitude should be emphasized as a key factor during the operation and maintenance of underground engineering.