The interaction between hydraulic fractures and natural fractures is a key factor in the forming of complex networks during shale fracturing. In spite of abundant natural filling fractures having been found in practical shale layers, previous studies have either ignored the effects of natural fractures or highly simplified them. In order to investigate how the natural filling fracture effect on crack propagation, in this paper, the central straight notched Brazilian discs (CSNBD) of shale under different loading angles were used to study the crack initiation and propagation via digital image correlation (DIC) method. The testing results reveal that the natural filling fracture leads to larger loading displacement, more active acoustic emission signals and lower strength, which indicates that the infillings may contain numerous micro-cracks, therefore, making the filling fracture a weak structure; The crack propagating path was unaffected when the filling natural fracture is parallel to loading line, while the natural filling fractures still on the risk of cracking due to the incompatible deformation between the natural infillings and the host rock; Besides, the initial cracking angle of the crack tip near the natural filling fracture increases while it decreases for the crack tip away from the natural filling fracture when the loading angle is 30°, 60° and 90°, nevertheless, for these discs without an infilling fracture, the two wing cracks are nearly symmetrical and initial cracking angles are almost equal. This research manifests that, on the laboratory scale, the failure modes and the cracking patterns of shale become more complicated when natural filling fractures exist. Therefore the influences of natural filling fractures could be even more significant when it is referred to the practical scale of on-site hydraulic fracturing, the related topics should be further studied in detail.

水力压裂与自然压裂之间的相互作用是页岩压裂过程中复杂网络形成的关键因素。尽管在实际的页岩层中发现了大量的天然填充裂缝，但先前的研究要么忽略了天然裂缝的影响，要么对其进行了高度简化。为了研究自然填充裂缝对裂缝扩展的影响，本文采用页岩中央直缝巴西圆盘（CSNBD）在不同加载角下通过数字图像相关（DIC）方法研究裂缝的萌生和扩展。 。测试结果表明，自然填充裂缝会导致更大的荷载位移，更多的活跃声发射信号和更低的强度，这表明填充物中可能包含许多微裂纹，因此，使填充物断裂成为弱结构；当填充天然裂缝与荷载线平行时，裂纹扩展路径不受影响，而由于天然填充物与基岩之间不相容的变形，天然填充裂缝仍具有开裂的风险。此外，当加载角为30°，60°和90°时，对于这些无应力的圆盘，在自然填充裂缝附近的裂纹尖端的初始开裂角会增加，而远离自然填充裂缝的裂纹尖端的初始开裂角会减小。填充裂缝中，两个机翼裂纹几乎对称，初始裂纹角度几乎相等。研究表明，在实验室范围内，当存在天然填充裂缝时，页岩的破坏模式和破裂模式变得更加复杂。