中文摘要：

阶梯状滑移破裂作为节理斜坡的一种典型破坏模式，裂隙间裂纹的扩展模式对其变形破裂机制及斜坡破裂面形态具有重要的意义。通过颗粒流程序研究了不同岩桥倾角（0°，45°，90°，135°）和围压条件下双裂隙间裂纹的贯通模式、基本特征与影响因素，揭示含双裂隙岩体在不同围压作用下裂纹扩展的细观力学机制，并推广到含多裂隙岩体裂纹扩展模式中。主要成果如下：①双裂隙的贯通主要通过次生共面裂纹、次生倾斜裂纹和翼裂纹；②裂纹扩展具有明显的围压效应，低围压条件下，裂隙的贯通主要通过翼裂纹和次生倾斜裂纹，高围压条件下，裂隙的贯通主要通过次生共面裂纹和次生倾斜裂纹；③裂隙的贯通应力受岩桥倾角影响较大，岩桥倾角为45°时，裂隙的贯通应力最小，裂隙最容易贯通。结合双裂隙贯通模式的研究，对多裂隙岩体贯通模式进行研究，多裂隙岩体贯通模式可以理解为多组双裂隙的贯通模式的不同组合，同时，在多裂隙贯通模式中，裂纹会寻找贯通应力最小路径扩展。最后，结合一实际斜坡案例，对阶梯状破坏斜坡的基本破裂特征进行了总结分析，并提出了相应的破裂模式分区。

英文摘要：

The crack propagation and coalescence mode play an important role in the step-path failure mechanism of rock slopes. By using the discrete element method （DEM）, the coalescence modes between two pre-existing cracks with different geometries （rock bridge angle） and confining stresses under biaxial compression are performed. Three types of cracks can be identified during the tests, which are the secondary coplanar cracks, secondary inclined cracks and wing cracks. Meanwhile, the wing cracks and secondary inclined cracks occur under a low confining stress biaxial compression and almost disappear under a high confining stress. Based on the above, the step-path failure mechanism of multiple flaws is investigated. It is found that the crack coalescence modes depend on the coalescence stress severely, and the extended modes are carried out and show the homologous view. Finally, taking a rock slope as an example, the mechanism of rock slope step-path failure is generalized. The coalescence of the joints is from bottom to upper, and the coalescence mode of the joints is subjected to the slope stress conditions. Based on the modes of crack coalescence and correlation between crack coalescence modes and stress, three zones of the failure surface are divided.