The discrete element method (DEM) has been used to investigate the mechanical and failure behavior and the associated micro-cracking process of mudstone under the hollow cylinder torsional test by using a commercial DEM code PFC3D. Micro-parameters of the numerical model were first calibrated to the experimental results of the uniaxial compression tests and the uniaxial tensile tests. Based on the calibration results, numerical hollow cylindrical torsional shear tests were carried out under three typical stress conditions, i.e. triaxial compression, torsional compression and pure torsional shear. The numerical results show that the mechanical behavior of mudstone, in terms of rock strength, micro-crack initiation and propagation, and failure mode, can be significantly affected by principal stress rotation, which is in line with previous experimental results. The analysis of the micro-crack process confirms that the principal stress rotation plays an important role in the initiation and propagation of micro-cracks. It is shown that the microcracks induced by tensile stress occur in a preferential direction parallel to the major principal stress ${\sigma }_1$, while the orientation distribution of the shear micro-cracks is related to the shear bands. Furthermore, the initial micro-crack stress is found to decrease after introducing the principal stress rotation, which provides a new interpretation of degradation of strength and permeability of mudstone under principal stress rotation. Three typical failure modes of specimens in different loading states are reproduced in this study, and the microscopic mechanism is also discussed. Based on this study, it is found that ignoring the principal stress rotation may overrate the stability and tightness of underground storage in bedded rock salt caverns.

离散元方法 (DEM) 已被用于通过使用商业 DEM 代码 PFC3D 研究空心圆柱扭转试验下泥岩的力学和破坏行为以及相关的微裂纹过程。首先根据单轴压缩试验和单轴拉伸试验的实验结果校准数值模型的微观参数。根据标定结果，在三轴压缩、扭转压缩和纯扭转剪切三种典型应力条件下进行了数值中空圆柱扭转剪切试验。数值结果表明，泥岩的力学行为，在岩石强度、微裂纹萌生和扩展、破坏模式等方面，受主应力旋转的影响显着，这与之前的实验结果一致。对微裂纹过程的分析证实，主应力旋转在微裂纹的萌生和扩展中起重要作用。结果表明，拉应力引起的微裂纹沿与主要主应力平行的优先方向发生${\sigma }_1$，而剪切微裂纹的取向分布与剪切带有关。此外，还发现引入主应力旋转后初始微裂纹应力降低，为主应力旋转下泥岩强度和渗透率退化提供了新的解释。本研究再现了试样在不同加载状态下的三种典型失效模式，并讨论了微观机制。基于本研究发现，在层状岩盐洞室中，忽略主应力旋转可能会高估地下储存的稳定性和密封性。