To investigate the crack evolution of Longmaxi shales with a single prefabricated fissure, a CCD (charge coupled device) camera and AE (acoustic emission) monitoring equipment were employed. On the basis of real-time CCD photographs and AE events, a real-time crack evolution process in fissured shale specimens under uniaxial compression was investigated. The crack initiation angle and extension angle were calculated, the relationship between the crack initiation stress, strength, and crack angle was compared, and the proportion of tensile and shear cracks at different stages of the whole compression process was briefly analyzed. The results demonstrate that, with the increase in fissure angle (α), the weakening ability of the prefabricated fissure to uniaxial compressive strength and crack initiation stress was reduced. The initial cracks and secondary cracks always appeared at the tip of the pre-existing fissure in the form of tensile cracks for α = 30–90°. The crack initiation angle and expansion angle increased first and then decreased rapidly with α increasing. Furthermore, the ultimate failure modes were mixed tensile and shear failure when α = 0–90°. The crack evolution of the fissured shale was progressive, but the final failure of the fissured specimen occurred rapidly. Furthermore, the appearance of the cracks, stress drops, and AE counts had good consistency in time.

中文翻译：

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含预裂页岩受压裂缝演化及破坏模式

为了研究具有单个预制裂缝的龙马溪页岩裂缝演化，采用CCD（电荷耦合器件）相机和AE（声发射）监测设备。在实时CCD照片和AE事件的基础上，研究了单轴压缩下裂隙页岩标本的实时裂纹演化过程。计算了裂纹萌生角和扩展角，比较了裂纹萌生应力、强度与裂纹角之间的关系，简要分析了整个压缩过程不同阶段的拉剪裂纹比例。结果表明，随着裂隙角（α）的增加，预制裂隙对单轴抗压强度和裂纹萌生应力的弱化能力降低。初始裂纹和二次裂纹总是以α = 30-90°的拉伸裂纹形式出现在预先存在的裂纹尖端。随着α的增加，裂纹萌生角和扩展角先增大后迅速减小。此外，当 α = 0-90°时，最终破坏模式是拉伸和剪切混合破坏。裂隙页岩的裂缝演化是渐进的，但裂隙标本的最终破坏发生得很快。此外，裂纹的出现、应力下降和 AE 计数在时间上具有良好的一致性。当 α = 0-90°时，最终破坏模式是拉伸和剪切混合破坏。裂隙页岩的裂缝演化是渐进的，但裂隙标本的最终破坏发生得很快。此外，裂纹的出现、应力下降和 AE 计数在时间上具有良好的一致性。当 α = 0-90°时，最终破坏模式是拉伸和剪切混合破坏。裂隙页岩的裂缝演化是渐进的，但裂隙标本的最终破坏发生得很快。此外，裂纹的出现、应力下降和 AE 计数在时间上具有良好的一致性。