| In view of the frequent occurrence of uneven joint fractures in rock mass engineering and causing instability and damage as the background,in order to study the early warning measures and improve the safety early warning effect,this paper uses acoustic emission technology and image analysis technology to systematically study the performance characteristics of internal micro-fractures and the dynamic evolution of cracks in the process of fracture instability of rocks containing prefabricated cracks,and conducts experimental studies on the failure characteristics of gypsum materials containing prefabricated cracks under uniaxial compression conditions and the corresponding PFC2 D numerical simulation experiments,and the roughness of prefabricated joints is 1,3,5,7,Grade 9,inclination angles of 0 °,30 °,45 °gypsum specimens for uniaxial loading chamber test.The indoor test uses acoustic emission technology and image analysis technology to carry out the experiment,acoustic emission technology can monitor the micro-rupture signal during the loading process of the test piece;the image analysis technology is to use the digital image correlation method(DIC)to analyze the change of the whole-field strain concentration area during the loading process,and the second is to use particle velocimetry technology(PIV)to observe the displacement change of the surface of the specimen during the loading process and determine the specific types of initial cracks and secondary cracks.Finally,PFC2 D was used to perform numerical simulations,and the crack failure category,number of cracks and failure types of cracks were analyzed again after the rock-like material was loaded into the failure.The conclusions of this paper are as follows:(1)According to the analysis of the mechanical characteristic curve,it is concluded that the strain drop of the specimen with an inclination angle of 0° is more numerous and denser than that of the specimen at 30° and 45°,and the time is more advanced;the relative compressive strength of the specimen with an inclination angle of 0° is higher,and the compressive strength of the inclination angle of 45° is lower.For 0° inclination specimens,the compressive strength gradually decreases with the increase of JRC grade;for specimens with 30° and 45° inclination angles,the compressive strength gradually increases with the increase of JRC grades.There are also significant differences in the residual strength after peaks,in the 30° and 45° specimens,as the JRC increases,the residual strength will change in a stepped manner,and it will not be completely destroyed directly like brittle rock.(2)In the initial compaction stage,the ringing count and energy of all specimens are at a low level,and the acoustic emission event is not active.During the elastic deformation phase,the ringing count and energy values of some specimens increased,but the overall increase did not reach the maximum value.During the yield phase,the ringing count and energy values increase significantly and are very dense,and the cumulative ringing count and cumulative energy also show a sharp increase.In the post-peak stage,the ringing count value is reduced,there are still certain acoustic emission events,the specimen produces macroscopic damage,and there will be secondary cracks in the later stage,but it is macroscopic destruction,and the inside of the specimen is not accompanied by a large number of unbroken,resulting in a low sound emission ringing count value in the later stage,and the acoustic emission event is not active.According to the specimen with an inclination angle of 45°,due to the difference in joint fractures,the concentrated energy end time of the high value of the elastic deformation stage will gradually be postponed to the late peak period with the increase of the roughness level.The accumulated energy grows steadily in the compaction stage and the elastic deformation stage,accelerates to the yield stage,and grows steadily again in the post-peak stage.(3)According to the ROI image,DIC strain cloud diagram,PIV displacement vector diagram,the DIC strain cloud map observes that the strain before the peak is dispersed and low value,the initial cracks of the peak segment appear,all of which are wing cracks,the strain of the wing crack area is concentrated and the strain value increases,the secondary crack appears in the late peak period,the strain concentration area changes or increases,and the strain value increases.In the PIV graph,it is observed that the overall direction of the characteristic point displacement before the peak is consistent with the loading direction,and the size is basically equal,and the initial crack appears at the peak stage,and the initial crack is a tensile crack,and the secondary crack is observed in the late loading stage,and the secondary crack is mainly shear crack.According to the statistics of the crack generation type of various specimens,direct tensile cracks are reflected in specimens with different inclination angles,mainly wing cracks,some far-field cracks,and secondary cracks are mainly shear cracks or tensile shear cracks.(4)Use PFC2D numerical simulation to analyze the force chain field diagram,displacement field diagram and crack diagram of the specimen.The study found that the model failure type of0° and 60° inclination angle is typical X-conjugate slope shear failure,and the 45° inclination model not only has X-conjugate slope shear failure,but also has single-slope shear failure.The30° inclination model failure type is similar to the X-conjugate slope shear crack,but is not identical.According to the monitoring of the number of cracks,the number of cracks in the 30°inclination model is the smallest,and the number of cracks at the 60° inclination angle is the largest.It is also concluded that the crack types in the 0°,30° and 45° inclination models are relative tensile cracks(RT)and tensile shear cracks(ST),and the crack types in the 60°inclination model are relative tensile(RT),relative shear(RS)and tensile shear cracks(ST). |
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