Experimental Study On Shale Compression Damage Based On Acoustic Emission Technology

In order to study the real damage evolution mechanism of shale,to explore the influence of bedding direction and confining pressure on the mechanical properties of shale rock,and to establish the shale damage constitutive equation,using acoustic emission technology,the single and triaxial compression acoustic emission experiment,shale Brazil splitting experiment,shale type I fracture toughness test experiment were carried out.The characteristics of rock mechanics such as shale damage evolution,rock failure,acoustic emission signal and stress-strain are analyzed under different confining pressures and different bedding directions,and reasonable theoretical analysis is given.The results show that the micro holes,micro cracks,macro cracks and bedding in the initial stage of loading are compacted,the damage is reduced,the slope of stress-strain curve is increasing,the elastic modulus of shale is not decreasing but increasing,the curve is concave,the damage of the loaded rock is not monotonous increasing,but first decreasing and then increasing.A more reasonable damage constitutive equation of shale under uniaxial compression based on acoustic emission characteristics is established.The stress-strain curve obtained from the established constitutive equation is more consistent with the actual stress-strain curve,which complements and improves the previous damage theory.The AE probe can capture the information of rock compaction,crack propagation and connectivity,and the AE signal can reflect the micro damage evolution process in shale.The AE signal is only related to the damage evolution,but not to the severity of the damage change.The AE signal always has a linear relationship with the damage.The bedding belongs to weak cemented surface,which has an important influence on the tensile strength and I-type fracture toughness of shale.The anisotropy of the tensile strength and I-type fracture toughness of shale in different bedding directions is obvious.When scientific research is conducted on the bedding rock,the bedding effect can not be ignored.The confining pressure makes the internal contact of shale closer,reduces the influence of initial damage such as pores and fractures on the rock properties,enhances the shale's ability to resist compression,weakens the shale's brittleness and enhances its plasticity.Different confining pressures lead to different rock failure patterns,and different confining pressures lead to different acoustic emission signal characteristics.Due to theinfluence of bedding,the rock damage evolution and acoustic emission characteristics in the direction of parallel bedding plane and vertical bedding plane are quite different.