单轴压缩下层状含水页岩损伤破坏过程及特征

Damage process and characteristics of layered water-bearing shale under uniaxial compression

页岩在重庆地区分布较广,在隧址围岩赋存环境中占较大比重,考虑到层理和水对页岩性质影响显著,因此,对页岩在层理和含水率影响下损伤破坏过程和劣化机制进行研究。试验借助于MTS815岩石力学测试系统和PAC声发射仪,进行单轴压缩条件下层状页岩损伤破坏过程的声发射试验研究,并采用大型离散元软件3DEC对页岩破坏模式进行对比分析。研究结果表明:(1)页岩的矿物成分、矿物排列和加载方向决定其损伤破坏过程,原生微裂隙的分布、矿物晶粒大小和加载方向决定了宏观裂隙的分布,宏观裂隙则控制着页岩的破坏模式。(2)页岩内部沿层理方向原生微裂隙群是页岩破坏起裂部位,次生微裂隙常沿矿物边界发展,与加载方向基本一致,最终形成宏观裂隙,起到连通层理破裂面的作用。(3)层状页岩AE事件的生成和分布与试件内部的微裂隙分布关系密切,初始压密阶段积聚于试件中部层理附近,后沿层理法向方向向端部或两侧发展,最终沿宏观裂隙转折及交点处聚结成核。(4)层理和水对页岩的损伤劣化机制不同,层理对页岩的损伤作用本质上是沿层理分布的原生微裂隙群的损伤作用,而水对页岩的损伤作用主要是水的吸附和毛细管压力作用。

Shale ＇widely distributed in Chongqing Region particularly accounts for a relatively large proportion in the surrounding tunnel of rock mass. The stratification and water significantly .affect mechanical properties of shale, this study is to investigate the damage process of shale and its deterioration mechanism under the influence of stratification and water content using the MTS815 testing system and PAC acoustic emission （AE） instrument. AE experiments were performed in the damage process of layered shale under uniaxial compression. The damage mode of shale was further analyzed comparatively using the commercial software 3DEC. The damage process of shale was determined by its mineral component, mineral arrangement and loading direction. The distribution of macro-cracks was dominated by the distribution of pre-existing micro-crack, the size of mineral grain and loading direction. Moreover, the macro-cracks governed the damage mode of shale. The pre-existing micro-fissuring group towards the stratification direction inside the shale triggered the damage zones of shale. The secondary micro-cracks were generally found along the mineral boundary, which basically had the same direction as the loading direction. These micro-cracks were formed the macro-cracks, which connected the damaging surfaces of stratifications. The AE events of generation and distribution of layered shale were closely related to the distribution of micro-cracks inside the trial piece. The initial compression phase accumulated near the stratification in the central section of shale, then developed towards its ends or both sides along the normal direction of the stratification. It finally coalesced to the core along the turning point and intersection position of macro-cracks. The stratification and water had different damage and deterioration mechanism on shale. The effect of stratification on shale was essentially the damage effect of pre-existing micro-cracks group distributed along the stratification. However, the damage effect of water on-shale is primarily depending on the water absorption and eepillary pressure.