Shale contains a certain amount of natural fractures, which affects the mechanical properties of shale. In this paper, a bonded-particle model in particle flow code (PFC) is established to simulate the failure process of layered shale under Brazilian tests, under the complex relationship between layer plane and natural fracture. First, a shale model without natural fractures is verified against the experimental results. Then, a natural fracture is embedded in the shale model, where the outcomes indicate that the layer plane angle (marked as α) and the angle (marked as β) of embedded fracture prominently interfere the failure strength anisotropy and fracture pattern. Finally, sensitivity evaluations suggest that variable tensile/cohesion strength has a changeable influence on failure mechanism of shale, even for same α or/and β. To serve this work, the stimulated fractures are categorized into two patterns based on whether they relate to natural fracture or not. Meanwhile, four damage modes and the number of microcracks during the loading process are recognized quantitatively to study the mechanism of shale failure behavior. Considering the failure mechanism determines the outcome of hydraulic fracturing in shale, this work is supposed to provide a significant implication in theory for the engineering operation.

页岩含有一定数量的天然裂缝，这会影响页岩的机械性能。本文建立了颗粒流代码（PFC）中的键合颗粒模型，以模拟层状页岩与自然裂缝之间的复杂关系，模拟巴西试验下的层状页岩的破坏过程。首先，对照实验结果验证了没有天然裂缝的页岩模型。然后，将天然裂缝嵌入页岩模型中，结果表明层平面角（标记为α）和角度（标记为β））的嵌入断裂明显地破坏了破坏强度的各向异性和断裂模式。最后，敏感性评估表明，即使相同的α或/和β，可变的抗张强度/内聚强度对页岩的破坏机理也具有可变的影响。为了完成这项工作，根据受激裂缝是否与天然裂缝有关，将其分为两种类型。同时，定量识别了加载过程中的四种破坏模式和微裂纹数量，以研究页岩破坏行为的机理。考虑到破坏机理决定了页岩水力压裂的结果，这项工作在理论上为工程运营提供了重要的启示。