Study On Mechanical Properties And Acoustic Emission Rules Of Granite Under Monotonic And Cyclic Compression

The mechanical properties of rock under cyclic loading are related to the construction of underground projects such as subway and tunnel,the excavation and reinforcement of the rock mass,the multiple blasting excavation of underground chamber and the mining and construction of coal mine working face,etc.At present,the damage evolution law of rock under cyclic loading combined with acoustic emission detection technology is still relatively few.In view of the theory of rock mechanics,laboratory tests are carried out by the paper combined with numerical simulation techniques,the work developed and the conclusions drawn are as follows:Firstly,uniaxial and triaxial compression tests were carried out by using MTS 815 test system,and the strength,deformation and energy dissipation characteristics of Huashan granite have been explored.The results show that the granite has obvious brittle characteristics.The“concave-upward”phenomenon of axial stress-strain curves from triaxial tests is less obvious than those from uniaxial tests.The elastic modulus and the strain corresponding to the peak stress increase with the increase of confining pressure.The elastic strain energy of the rock sample is mostly transformed into dissipated energy once the peak stress is reached under uniaxial,demonstrating evident splitting failure.As for triaxial of the samples,the ratio of dissipated energy to absorbed energy increases with the increase of confining pressure,accompanied by a general shear failure.Additionally,there is a linear relationship between the confining pressure and the absorbed energy,the dissipated energy and the energy storage limit.Then,uniaxial and triaxial cyclic loading-unloading compression tests were carried out,the characteristics of strength,deformation and damage along with acoustic emission under cyclic loading have been studied.Test results show that the“migration”of hysteresis loops under the triaxial cyclic compression are not obvious than those under the uniaxial compression.The peak strength and peak strain have good linear relationship with confining pressure.In the uniaxial cyclic test,the specimen demonstrates columnar splitting failure.During the uniaxial and triaxial compression tests,the elastic modulus and the Poisson's ratio of the first five cycles increase with the increase of cycle times,while the elastic modulus decreases at the last loading-unloading cycle.A platform can be detected at each stage of the damage duration curve for the uniaxial cyclic loading,whereas it is not obvious in the triaxial test,implying the damage of rock specimen experiences a show growth.The damage parameters of the plastic strain-based show agreement with that of energy dissipation.Finally,the numerical simulation of uniaxial and triaxial monotonic compression and uniaxial cyclic compression test process was carried out by using RFPA^2D?Realistic Failure Process Analysis 2D?.The result shows the samples take on a tensile AE with the tensile failure elements under uniaxial compression,and the feature of diagonal cone failure is obvious.With the increase of confining pressure,the failure mode of the sample has gradually been changed from tensile failure to compression shear failure during the triaxial compression simulation,the type of AE also changes from tension AE to compression-shear AE.An axial splitting failure of the sample is presented under the uniaxial cyclic compression,and the type of AE is tensile AE.The Kaiser effect and failure characteristics of rock can be well illustrated by the numerical simulation in laboratory tests.The simulated stress-strain curves agree well with the experimental ones under the different confining pressures.However,the calculated elastic modulus and peak stress are slightly lower than the measured results,respectively.