Rocks frequently endure water environments and diverse cyclic loading from natural and anthropogenic sources across various damage stages. Understanding the mechanical and fatigue behavior of saturated rocks under different cyclic loading levels is crucial for the intelligent design and long-term stability of the slope. Here, we report several monotonic and cyclic compression tests conducted on red and cyan sandstones under dry and water-saturated conditions, coupled with acoustic emission (AE) monitoring. We analyzed key mechanical parameters such as peak stress and peak strain, as well as AE parameters including count and energy, and dominant frequency in AE spectra. Our findings reveal that elevated cyclic loading levels significantly reduce peak stress and increase peak strain in both dry and water-saturated rocks, with more pronounced effects observed under water-saturated condition. The cumulative AE count correlates positively with increasing cyclic loading levels but decreases due to water saturation. Under cyclic loading with varying levels, dry rocks often experience shear cracking and exhibit AE waveform with high dominant frequency, while saturated rocks tend toward tensile cracking and AE waveform with low dominant frequency. Higher cyclic loading intensifies the occurrence of tensile cracking and AE waveform with low dominant frequency, which are constrained during the elastic deformation stage but become more pronounced beyond the crack initiation threshold. Moreover, cyclic loading enhances the water weakening effects in saturated rocks, closely associated with ongoing crack propagation within the rocks.

中文翻译：

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循环加载水平对饱和砂岩力学响应和微裂行为的影响：与水弱化现象的相关性


岩石经常承受水环境和来自自然和人为来源的不同破坏阶段的不同循环载荷。了解饱和岩石在不同循环荷载水平下的力学和疲劳行为对于边坡的智能设计和长期稳定性至关重要。在这里，我们报告了在干燥和水饱和条件下对红色和青色砂岩进行的几次单调和循环压缩测试，以及声发射 (AE) 监测。我们分析了峰值应力和峰值应变等关键机械参数，以及包括计数和能量在内的 AE 参数，以及 AE 谱中的主频率。我们的研究结果表明，升高的循环载荷水平显着降低了干燥和水饱和岩石中的峰值应力并增加了峰值应变，在水饱和条件下观察到了更明显的影响。累积 AE 计数与循环负荷水平的增加呈正相关，但由于水饱和而减少。在不同程度的循环荷载作用下，干燥岩石常发生剪切开裂，并呈现出主频率较高的声发射波形，而饱和岩石则易发生拉伸开裂，并呈现出主频率较低的声发射波形。较高的循环载荷加剧了拉伸裂纹和主频率较低的声发射波形的发生，这些波形在弹性变形阶段受到限制，但在裂纹萌生阈值之外变得更加明显。此外，循环载荷增强了饱和岩石中的水弱化效应，这与岩石内持续的裂纹扩展密切相关。