基于离散元法的脆性岩石细观蠕变失稳研究

为从细观角度探究脆性岩石的蠕变失稳过程及失稳机理，该文基于三维颗粒流程序（PFC^3D）考虑岩石的时效变形损伤过程，引入岩石细观单元时效损伤的应力腐蚀模型，建立了基于离散元方法的岩石时效变形损伤破裂模型，并通过单轴压缩及单轴蠕变的室内实验和数值模拟对比验证了所建立的时效变形损伤破裂模型的合理性。数值模拟再现了岩石的初始蠕变、稳态蠕变和加速蠕变三个蠕变阶段，同时模拟结果表明，在单级加载条件下，随着应力水平提高，稳态蠕变应变率显著增大，岩石蠕变失效时间逐渐缩短，初始轴向应变、初始侧向应变和初始体应变不断增大，且细观裂纹扩展形式与单轴压缩破坏形式基本相同，都是以拉伸裂纹为主，裂纹的增长速率随着时间增加而不断增大，尤其在第三蠕变阶段裂纹增长速率迅速增大；在分级加载试验过程中，模型的轴向应变、侧向应变和体应变以及裂纹最终扩展形态与单级加载基本相同；此外将三维蠕变模拟结果与二维模拟结果进行对比，结果显示三维模型拟合程度更高。

A MICROSCOPIC STUDY OF CREEP AND FRACTURING OF BRITTLE ROCKS BASED ON DISCRETE ELEMENT METHOD

To analyze the creep process and creep mechanism of rock at a microscopic scale, a numerical model of time-dependent deformation and damage was established by incorporating the parallel-bonded stress corrosion model into the Particle Flow Code3D (PFC3D). The numerical model was validated against laboratory results. The numerical results replicated the typical three creep stages including the primary creep, secondary creep and tertiary creep. Meanwhile, the numerical simulation results indicate that the time-to-failure of creep decreases gradually with the increase of the stress level, while the initial axial strain, initial lateral strain, initial volume strain and creep strain rate gradually increase in this process. The crack propagation pattern in the uniaxial creep test is generally identical to that in the uniaxial compression test and the tension cracks are dominant. The crack growth rate increases with time and sharply increases in the tertiary creep stage. In the stress-stepping test, the axial strain, lateral strain, volumetric strain and the final propagation mode of the model are the same as that of the single-stage creep test. In addition, the comparisons between two-dimensional and three-dimensional creep simulation show that the three-dimensional modeling is more suitable than the two-dimensional modeling.