Study On Acoustic Emission Characteristics And Damage Model Of Shear Failure Of Bolted Rock Joints

Fractured rock mass is widely distributed in complex geological environment,which is composed of rock blocks and structural planes.It is often considered and controlled in geotechnical engineering.Acoustic emission(AE)technology is often used as a nondestructive testing method for material performance or structural integrity.It has the advantages of real-time monitoring and high sensitivity.Fractal theory utilizes fractal dimension to describe and study objective things,which is closer to the description of real attributes and states of complex systems.The results show that the rock shear failure process has fractal characteristics in time and space.The fractal characteristics of rock acoustic emission parameters are analyzed,and the change of correlation dimension in the whole process of shear acoustic emission is calculated,combining with rock meso-damage mechanics model.This paper attempts to establish a method for calculating directly the crack density of rock meso-variable based on macro-angle.The main research contents and achievements are shown as follows:(1)During the compression stage of micro-cracks in shear acoustic emission test,the stress characteristic curve is concave,and the corresponding acoustic emission events are relatively few.With the increase of stress,the micro-cracks close gradually and enter the stage of elastic deformation,at which time the acoustic emission events are less.When the stress reaches the initiation strength,the micro-cracks in the rock begin to initiate and expand,and the corresponding acoustic emission events also increase steadily.When the peak stress is approaching,the number of acoustic emission rings increases rapidly,and the rock interior has begun to yield.Acoustic emission events are still active after peak strength,micro-cracks in rock have been connected and broken,and the protruding friction failure of structural plane has entered the stage of residual friction strength.(2)According to the principle of GP algorithm and one-dimensional time series,the m-dimensional phase space is constructed.The data samples of the acoustic emission count rate are taken as the research object,and the fractal characteristics of the acoustic emission ringing count of rock are analyzed.In order to study the evolution process of the correlation dimension,the correlation dimension of the rock acoustic emission is calculated once every 2%displacement.Comparing the shear-displacement curve with the change curve of the correlation dimension D2,it is found that the correlation dimension of the rock shear failure is consistent with the evolution process of the crack inside the rock.(3)The curve between the acoustic emission ringing count and the displacement load is expressed as a function of the power function.By normalizing the cumulative ringing count of acoustic emission,an important parameter of the meso-damage evolution of rock is obtained,and it is taken as an important parameter in the meso-damage mechanics--crack density factor.A damage model based on the characteristics of the acoustic emission parameters is then established.The stress-displacement curve drawn by the acoustic emission damage model is compared with the experimental curve.It is found that the curve in the initial crack compaction phase is similar to the crack stable expansion phase.In the post-peak strength stage,the strength of the rock is mainly derived from the residual frictional strength of the structural plane,so the acoustic emission damage model is slightly lower than the test curve.