Study on Acoustic Emission of the Fractal Characteristics of the Stratified Shale Under Uniaxial Compression
It is of great significance to study the mechanical characteristics of the stratified shale from different angles and detect the fracture instability process of the stratified shale through the reasonable monitoring technology to ensure the production effi-ciency of the shale gas and the stability of drilling operations.In this paper,the shale samples with different bedding angles were tested by the uniaxial compression,and the fracture process was recorded by the acoustic emission monitoring method.The experimental results show that the uniaxial compressive strength of the stratified shale has strong anisotropy characteris-tics.With the increase of the bedding angle,the uniaxial compressive strength decreases first and then increases.The uniaxial failure types of the bedding shale at different angles are obviously different.The failure types are mainly tensile failure at 0° and 90°,and shear failure at 30° and 60°.The correlation dimension D of the acoustic emission time series based on the fractal theo-ry can well characterize the development and evolution law of damage and the failure inside the stratified shale.The fluctuation of the correlation dimension D at a high value indicates that the microcracks are mainly formed inside the stratified shale,while the sharp decline of correlation dimension D indicates the occurrence of large-size cracks.That is,the sharp decline of the cor-relation dimension D can be used as the early warning information of the imminent instability failure of bedding shale.
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