The propagation and coalescence of numerous discontinuous joints significantly contribute to landslide instability during excavation unloading. The tip expression of stress intensity factors of two collinear unequal length cracks in a typical rock mass under unloading conditions was calculated based on the superposition principle and fracture mechanics to determine the meso-influence law of intermittent joint interaction in the slope under the action of excavation. The effects of many factors on this interaction were also analyzed theoretically. Unloading tests were conducted on rock-like specimens with two collinear unequal length cracks in addition to numerical simulation and theoretical analysis. The results show decreased interaction between the two cracks with increased crack distance, increased influence of the main crack on a secondary crack with increased length of the main crack, and decreased influence of the secondary crack on the main crack with decreased length of the secondary crack. Wing tensile cracks first appear at the tip of flaws, and the propagation of these cracks occurs with the generation of secondary tensile cracks and shear cracks during unloading. Propagation and coalescence between cracks lead to tension and shear mixed failure of a rock bridge, and tensile cracks appear near the unloading surface. The axial initiation and peak stress of a crack increase with increased flaw distance, and the theoretical calculations were confirmed by lateral unloading test results.

中文翻译：

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脆性岩石中两个共线不等长缺陷的卸载诱导裂纹扩展

许多不连续节理的扩展和合并显着导致开挖卸载过程中的滑坡不稳定。基于叠加原理和断裂力学计算卸载条件下典型岩体中两条共线不等长裂缝应力强度因子的尖端表达式，确定开挖作用下边坡间断节理相互作用的细观影响规律. 还从理论上分析了许多因素对这种相互作用的影响。除了数值模拟和理论分析外，还对具有两条共线不等长裂缝的类岩石试样进行了卸载试验。结果表明，随着裂纹距离的增加，两个裂纹之间的相互作用减少，随着主裂纹长度的增加，主裂纹对二级裂纹的影响增加，而随着二级裂纹长度的减小，二级裂纹对主裂纹的影响减小。翼部拉伸裂纹首先出现在裂纹尖端，这些裂纹随着卸载过程中二次拉伸裂纹和剪切裂纹的产生而扩展。裂缝之间的扩展和合并导致岩桥的拉剪混合破坏，在卸荷面附近出现拉伸裂缝。裂纹的轴向起始应力和峰值应力随着裂纹距离的增加而增加，横向卸载试验结果证实了理论计算。并且随着二次裂纹长度的减小，二次裂纹对主裂纹的影响减小。翼部拉伸裂纹首先出现在裂纹尖端，这些裂纹随着卸载过程中二次拉伸裂纹和剪切裂纹的产生而扩展。裂缝之间的扩展和合并导致岩桥的拉剪混合破坏，在卸荷面附近出现拉伸裂缝。裂纹的轴向起始应力和峰值应力随着裂纹距离的增加而增加，横向卸载试验结果证实了理论计算。并且随着二次裂纹长度的减小，二次裂纹对主裂纹的影响减小。翼部拉伸裂纹首先出现在裂纹尖端，这些裂纹随着卸载过程中二次拉伸裂纹和剪切裂纹的产生而扩展。裂缝之间的扩展和合并导致岩桥的拉剪混合破坏，在卸荷面附近出现拉伸裂缝。裂纹的轴向起始应力和峰值应力随着裂纹距离的增加而增加，横向卸载试验结果证实了理论计算。裂缝之间的扩展和合并导致岩桥的拉剪混合破坏，在卸荷面附近出现拉伸裂缝。裂纹的轴向起始应力和峰值应力随着裂纹距离的增加而增加，横向卸载试验结果证实了理论计算。裂缝之间的扩展和合并导致岩桥的拉剪混合破坏，在卸荷面附近出现拉伸裂缝。裂纹的轴向起始应力和峰值应力随着裂纹距离的增加而增加，横向卸载试验结果证实了理论计算。