Abstract: 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 capillary pressure.

Key words: layered shale, water content, 3DEC, acoustic emission, damage