Mechanical And Acoustic Emission Characteristics Of Rock Joint Shear Failure Under Cyclic Loading

In the field of geotechnical engineering,the cyclic load caused by natural factors or human activities is easier to induce structural instability than static load,especially for the geotechnical structure with unstable discontinuities such as joints caused by geological movement or construction.It is difficult to accurately understand the damage development of geotechnical structure in the cyclic process and to monitor and warn the instability of rock engineering.Because of the advantages of acoustic emission technology in the evaluation of material damage evolution and structural damage monitoring and early warning,the mechanical test with acoustic emission monitoring can make us more comprehensive understand the damage evolution of rock materials under cyclic load,which is of great significance for the evaluation of rock and soil service life and the early warning of in-service structural instability.Therefore,based on the theory of rock mechanics and acoustic emission technology,this thesis explores and analyzes the damage evolution,strength evolution and acoustic emission precursor information of rock joint shear failure under cyclic shear by using the research methods of indoor test and numerical simulation.The research results provide a reference for evaluating the service life of geotechnical structure and rock slope landslide Disaster monitoring and early warning can provide some reference.The main contents and achievements of this thesis are as follows:(1)Cutting original rock with water knife to make rock joint sample and the direct shear test is carried out in the laboratory.The test results show that the deformation and failure mode of the specimen is affected by the normal stress and the first-order fluctuation angle.On the basis of different deformation and failure modes,the pre peak cyclic shear tests of rock joints are carried out,and the influence of cyclic loading times on the damage characteristics of rock joints is analyzed.According to the cumulative deformation and acoustic emission release law of rock joints during cyclic loading,it is known that the damage development rate of rock joints is first fast and then slow with the increase of cyclic loading times,and this evolution is progressive Due to the influence of the deformation characteristics of rock joints,the damage accumulation of rock joints in climbing failure mode is obvious only in the initial stage of loading,and the subsequent cyclic loading will not cause new damage to the joint surface.The cumulative damage of the other two rock joints is more obvious with the increase of the number of cycles.(2)Through the acoustic emission monitoring during the whole process of the test,it is found that the acoustic emission technology has sufficient accuracy to monitor the cyclic shear process of rock joints.The more severe the rock joint failure is,the more obvious the acoustic emission energy is released.The dynamic acoustic emission B value based on seismology has the ability of rock failure monitoring and early warning The cyclic loading of rock joints reproduces the AE memory effect of rock materials,but this memory effect is different from the usual results of rock compression tests,and will affect the ability of rock failure monitoring and early warning by acoustic emission technology.(3)Using particle flow software(PFC2D)to carry out the numerical simulation research,by loading in the process of crack evolution and energy release rate,further from the perspective of mesoscopic damage accumulation process of different deformation modes of rock joints are analyzed and acoustic emission features,the numerical simulation results show that the activated again closer to the damage acoustic emission phenomenon also has the ability of rock damage monitoring and early warning,on the basis of normal stress is discussed further The research shows that the higher first-order undulation Angle will increase the cyclic shear capacity of rock joints to some extent,while the increase of normal stress will significantly reduce the cyclic shear capacity.(4)Combined with laboratory test and numerical simulation results are discussed with the first cyclic shear shear properties of rock joints,the influence of the shear strength,shear strength of rock joints under the first a cyclic shear evolution trend is influenced by the deformation characteristics of rock joints,the first a cyclic loading basic will not reduce the shear strength of rock joints are climbing failure mode,the rest of the rock joints under two kinds of failure modes The shear strength decreases gradually with the cyclic loading,and the residual strength of rock joints after failure is not affected by the prior cyclic loading,and a small amount of the prior cyclic loading tends to lead to the failure of rock joints under smaller shear displacement.