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饱水作用对砂岩变形及强度特征影响显著,考虑岩体实际赋存环境,为了解复杂应力路径下饱水砂岩宏细观力学特性,利用RMT-150C岩石力学多功能试验机及SEM电镜扫描技术,对饱水砂岩进行循环荷载作用后卸荷破坏试验,研究不同影响因素作用下的疲劳损伤特征,重点分析了加载频率、上限应力等因素对卸荷变形、强度及细观损伤特征的影响规律。研究表明,根据试验设计方案获得的饱水砂岩应力-应变曲线大致可以划分为5个典型阶段,其中,同一应力状态下,疲劳损伤阶段轴向不可逆应变在等速变形阶段的应变速率随加载频率的增大迅速增加,这表明上限应力的“门槛值”极有可能是变化的,且与加载频率及循环次数密切相关;同时,卸围压变形破坏阶段的总应变及围压卸荷量均随加载频率(或上限应力)的增大而减小,与该阶段持续时间随加载频率(或上限应力)的变化规律一致。不仅如此,通过分析饱水砂岩破坏面细观损伤特征发现,加载频率与上限应力作用下的细观损伤特征差异显著,其中破坏面微裂隙面积占比随加载频率增大而减小,上限应力则恰好相反。
The effect of water saturation on the deformation and strength characteristics of sandstone is significant. Considering the actual occurrence environment of the rock mass, in order to understand the macro-meso-mechanics properties of the saturated water sandstone under complex stress path, using RMT-150C rock mechanics multi-function testing machine and SEM scanning technology , The unloading damage test of saturated sandstone after cyclic loading was carried out and the fatigue damage characteristics under different influence factors were studied. The influence of loading frequency and upper limit stress on the characteristics of unloading deformation, strength and mesoscopic damage was analyzed emphatically . The results show that the stress-strain curves of saturated sandstone can be divided into five typical phases according to the experimental design. Among them, under the same stress state, the strain rate of the axial irreversible strain during the fatigue damage phase at constant velocity is dependent on the loading frequency Which indicates that the “threshold value” of the upper limit stress is most likely to vary, and is closely related to the loading frequency and the number of cycles. Meanwhile, the total strain and the unloading of confining pressure during the deformation and failure of the unloading confining pressure The volume decreases with the increase of the loading frequency (or the upper limit stress), which is consistent with the variation of the duration of this phase with the loading frequency (or the upper limit stress). Not only that, but also through the analysis of the meso-damage characteristics of the destructible surface of saturated sandstone, it is found that there is significant difference between the mesoscopic damage characteristics under the loading frequency and the upper limit stress. The proportion of the microcrack area in the destructed surface decreases with the increase of the loading frequency. The opposite is true.