Weakly cemented sandstone (WCS) is a unique rock type widely distributed on the surface. Environmental factors such as groundwater and stress variations easily influence its fatigue mechanical properties and fracture characteristics. To design and evaluate the long-term stability of surrounding rock support in tunnel excavation and underground resource mining projects, investigating the fatigue mechanical properties and acoustic emission (AE) response characteristics of saturated WCS under different loading rates is of great practical and theoretical significance. This study employed experimental techniques such as X-ray diffraction (XRD), nuclear magnetic resonance (NMR), and natural water absorption tests to investigate the mineral composition, pore size, and connectivity characteristics of WCS. The multi-level cyclic loading-unloading tests (MCLU) combined with the AE system were conducted on dry and saturated WCS specimens at different loading rates. The results reveal that the deformation modulus of these specimens initially increases and then decreases under cyclic loading conditions. Water significantly influences the fatigue strength and deformation resistance of sandstone. As the loading rate increases, the range of RA values broadens, accompanied by a marked increase in the number of AE signals with high RA values. Saturated sandstone specimens are more prone to developing macroscopic shear fracture surfaces. Water has a more substantial effect on the stress distribution ranges corresponding to the response of the Kaiser effect in WCS than loading rates. The capacity of the Kaiser effect to indicate the extent of rock damage is intricately linked to the progression of internal micro-cracks. When internal damage surpasses the critical value of the Kaiser effect memory damage, the accelerated propagation of shear cracks becomes pivotal in the internal damage of the sandstone. It seems that the presence of water within the interior of the rock may facilitate the dissolution of K-feldspar in WCS, which could result in the formation of kaolinite, which will be further transformed into illite. The hydration expansion of illite may further exacerbate the deterioration effect of the mechanical properties of WCS.

中文翻译：

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不同加载速率条件下饱和弱胶结砂岩的疲劳力学性能和Kaiser效应特性


弱胶结砂岩 （WCS） 是一种独特的岩石类型，广泛分布在地表。地下水和应力变化等环境因素很容易影响其疲劳机械性能和断裂特性。为了设计和评价隧道开挖和地下资源开采工程中围岩支护的长期稳定性，研究不同加载速率下饱和WCS的疲劳力学性能和声发射（AE）响应特性具有重要的实践和理论意义。本研究采用 X 射线衍射 （XRD）、核磁共振 （NMR） 和自然吸水测试等实验技术来研究 WCS 的矿物成分、孔径和连接特性。结合 AE 系统对不同加载速率的干燥和饱和 WCS 试件进行多级循环加载-卸载测试 （MCLU）。结果表明：在循环加载条件下，这些试件的变形模量先增大后减小。水对砂岩的疲劳强度和抗变形能力有显著影响。随着加载速率的增加，RA 值的范围扩大，伴随着具有高 RA 值的 AE 信号数量的显著增加。饱和砂岩试件更容易形成宏观剪切断裂表面。与负载速率相比，水对对应于 WCS 中 Kaiser 效应响应的应力分布范围的影响更大。Kaiser 效应指示岩石损坏程度的能力与内部微裂纹的进展有着错综复杂的联系。 当内部损伤超过 Kaiser 效应记忆损伤的临界值时，剪切裂纹的加速扩展成为砂岩内部损伤的关键。岩石内部存在水似乎可能促进 K-长石在 WCS 中的溶解，这可能导致高岭石的形成，高岭石将进一步转化为伊利石。伊利石的水化膨胀可能进一步加剧 WCS 力学性能的劣化效应。