卸荷条件下岩体裂隙扩展贯通及能量演化机制

采用颗粒流软件PFC模拟了单轴压缩、双轴压缩和卸围压条件下裂隙倾角和岩桥倾角分别对含单裂隙和双裂隙岩体的裂纹扩展贯通的影响,对比分析了不同应力路径下裂隙岩体破裂演化过程,总结了裂纹扩展贯通模式,揭示了裂纹扩展贯通的细观力学机制和裂隙岩体损伤破裂的能量机制。研究表明:卸围压条件下岩样张性破坏略弱于单轴压缩条件但远强于双轴压缩条件,而剪性破坏远强于单轴压缩条件但略弱于双轴压缩条件;裂隙尖端应力集中导致岩体开裂,随后张性翼裂纹受拉应力场驱使沿拉应力释放区与压应力区边界延伸扩展,剪切裂纹受压应力场驱使,其扩展路径处压应力释放;裂隙岩体发生卸荷破坏时,内部损伤和贯通裂隙的产生会导致耗散能的急剧增加。

Mechanism of Crack Propagation,Coalescence and Energy Evolution of Rock Mass under Unloading Condition

The effects of fissure angle and rock bridge angle on crack propagation and coalescence of rock mass containing a single fissure and a fissure pair under uniaxial compression, biaxial compression and unloading confining pressure are simulated by PFC. Fracture processes of fractured rock mass under different stress paths are analyzed. The crack propagation and coalescence patterns are summarized. The mesomechanics of crack coalescence and the energy evolution of fractured rock mass are revealed. The study shows that: The tensile failure of rock samples under unloading confining pressure is slightly weaker than that under uniaxial compression condition, but much stronger than that under biaxial compression, and the shear failure is much stronger than that of uniaxial compression, but slightly weaker than that of biaxial compression condition. The stress concentration at the crack tip leads to crack initiation, and then the tensile wing crack is driven by the tensile stress field to extend along the boundary between the tensile stress release zone and the compressive stress zone, the shear crack is driven by the compressive stress field, and the compressive stress is released at its propagation path. Internal damage and penetrating crack will lead to a sharp increase in dissipated energy when unloading failure occurs.