为了探究复杂应力状态下岩体内缺陷（裂隙）的扩展与贯通机理，基于三维离散元软件（PFC3D）和改进的平行黏结模型（IPBM），模拟了双轴压缩试验中含双预制裂纹类岩石材料的裂纹扩展过程。通过逼近实验试件抗压强度、抗拉强度和弹性模量的宏观力学参数和裂纹扩展模式，调整数值模型微观参数。针对离散元模拟中的关键预制裂隙参数与围压对裂纹萌生、扩展及贯通过程的影响进行详尽的分析，结果表明：初始裂纹通常为拉伸裂纹，而次生裂纹通常为剪切裂纹，裂隙倾角主要影响初始裂纹位置；围压抑制初始裂纹，但促进次生裂纹发展；预制裂隙间的贯通裂纹与裂隙的参数和围压密切相关；围压σ_c > 0 MPa时，观察到两种新的剪切贯通类型（New1和New2）；数值试样中微裂纹的数量主要受围压影响，与裂隙参数无明显关联；试样的裂纹起始应力、峰值应力与围压和裂隙倾角相关，与岩桥长度和岩桥倾角无关；裂纹的扩展与试样内应力分布密切相关，裂纹最先在裂隙周围的应力集中区产生。结果为后续岩石与类岩石材料的离散元模型参数校准，以及基于离散元的裂纹扩展机理研究提供了可靠参考。

To explore the mechanism of extension and coalescence of the defect (flaw) in rocks under complex stress state, the study simulated the cracking process of rock-like material containing double pre-existing flaws in the biaxial compression test based on 3D discrete element software (PFC3D) and the improved parallel-bond model (IPBM). The microscopic parameters of the numerical model were calibrated by matching both macroscopic mechanical properties (uniaxial compressive strength, tensile strength, and elastic modulus) and cracking pattern with the laboratory experiments. The results show that: the first cracks are tensile cracks which vary with the inclination angle of flaw，and the secondary cracks are shear; the confining stress will suppress the first cracks and promote the development of the secondary cracks; the coalescence patterns of samples are closely related to the geometries of the flaw and the confining stress. Two new shear coalescence patterns (New1 and New2) can be observed at the confining stress σ_c > 0 MPa. The number of microcracks in the numerical sample is greatly affected by the confining stress, but not by the flaw geometries. The initial stress and peak stress of crack are correlated with confining stress and flaw inclination angle, but not with bridging length and bridging angle. The crack extension is closely related to the stress distribution in the sample, and the cracks first occur in the stress concentration area around the pre-existing flaws. The study provides a reliable reference for the subsequent calibration of discrete element model parameters and the crack extension mechanism based on discrete element.