Abstract Rock often suffers from discontinuous fatigue damages in geotechnical engineering, so it is of great significance to study deformation characteristics and failure modes of sandstone under discontinuous multi-level cyclic loading and unloading. By conducting continuous (only dynamic loading) and discontinuous (combined static and dynamic loading) multi-level cyclic loading and unloading tests, this study explored deformation characteristics and failure modes of sandstone. The test results demonstrated that the sandstone mainly suffered from large deformation dominated by dilation in circumferential direction when it was damaged after compression. After multi-level loading and unloading, evolution characteristics of deformation parameters showed characteristics of stepwise growth. However, the introduction of static loading changed such characteristics. In the process of combined static and dynamic loading, due to short action time, dynamic loading mainly promoted nucleation and sudden changes of cracks, while static loading affected crack development process mainly in the early compaction stage and late crack propagation and coalescence stage. Moreover, static loading showed small effects in elastic stage. In the compaction stage, the compacted micro-cracks reopened and cracks were affected by inertial damages in crack propagation stage and interconnected more thoroughly, so that the sandstone was finally more fragmented.

中文翻译：

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不连续多级循环荷载作用下砂岩变形特征及破坏模式

摘要 岩土工程中岩石经常发生不连续的疲劳损伤，因此研究砂岩在不连续多级循环加卸载下的变形特征和破坏模式具有重要意义。本研究通过连续（仅动态加载）和不连续（静态和动态加载组合）多级循环加载和卸载试验，探索砂岩的变形特征和破坏模式。试验结果表明，砂岩在受压破坏时主要发生以圆周方向膨胀为主的大变形。多级加载和卸载后，变形参数的演化特征呈现逐步增长的特征。然而，静态加载的引入改变了这种特性。在静动联合加载过程中，由于作用时间短，动加载主要促进裂纹的形核和突变，而静加载主要在压实早期和裂纹扩展及聚结后期影响裂纹发展过程。此外，静载荷在弹性阶段表现出很小的影响。在压实阶段，压实的微裂缝重新张开，裂缝在裂缝扩展阶段受到惯性损伤的影响，相互连接更加彻底，最终使砂岩更加破碎。而静载荷对裂纹发展过程的影响主要集中在早期压实阶段和晚期裂纹扩展与聚结阶段。此外，静载荷在弹性阶段表现出很小的影响。在压实阶段，压实的微裂缝重新张开，裂缝在裂缝扩展阶段受到惯性损伤的影响，相互连接更加彻底，最终使砂岩更加破碎。而静载荷对裂纹发展过程的影响主要集中在早期压实阶段和晚期裂纹扩展与聚结阶段。此外，静载荷在弹性阶段表现出很小的影响。在压实阶段，压实的微裂缝重新张开，裂缝在裂缝扩展阶段受到惯性损伤的影响，相互连接更加彻底，最终使砂岩更加破碎。