| In the construction of underground works,the excavation of the rock will lead to the unloading in one or more directions.Especially in the high ground stress area,the excavation of the rock leads to the suddenly release of huge energy which store in the rock mass.The excess energy is released in the form of kinetic energy of the rock mass and leads to the burst and eject of the rock,causing a huge threat to the safety of personnel,equipment and engineering.In this paper,the same added amplitude and the constant prescribed minimum uniaxial cyclic loading-unloading test,the uniaxial cyclic loading-unloading test with different amplitude disturbance,and the triaxial test with different confining pressure and different unloading ratio were done.And the deformation destruction mechanical property of marble in different unloading conditions was studied.And then the rock failure process analysis software RFPA2D numerical simulation was carried out to simulated the test that have done.The internal cracks and the distribution of acoustic emission of the rocks under different stress paths were analyzed.And the comparative analysis was given in the mechanical parameters include acoustic emission,failure pattern.The primary research results in this paper include:(1)according to the uniaxial cyclic loading-unloading and uniaxial cyclic loading-unloading with different amplitude disturbances experiments,the mechanical properties of the rock were studied,and the results shows that:(a)Under the cyclic loading the rock elastic modulus and poisson’s ratio of different cycle stages were increased with the increase of cycling times.The small amplitude disturbance behaved reinforcement in the rock elastic modulus.Compared with the uniaxial cyclic unloading without disturbance the poisson’s ratio was reduced after the disturbance load was applied,and that shows the disturbance load reduced the volume expansion of rocks.(b)Under cyclic loading and unloading,the rock is dominated by longitudinal splitting,and the difference of rock failure under different stress paths is reflected in the long thick ratio.(2)Different initial confining pressure and unloading rate triaxial test were conducted to study the mechanical characteristics,acoustic emission,failure pattern,etc.The results show that:(a)the initial confining pressure has the obvious reinforcement to the rock,(b)Some distinguish of the mechanical characteristics between different unloading rate,with the increasing of the unloading rate,the rock damage confining pressure,the residual stress present different patterns.And the deviator stress,the reduction value of the confining pressure of the dilatancy and the maximum deformation modulus,the average acoustic emission ringing counts in the process of unloading increase firstly and then decrease with the increasing of the unloading rate.The rupture angle decreases firstly and then increases with the improvement of unloading rate.(c)The number of small cracks in the macroscopic fracture surface of the rock decreasewith the increase of the initial confining pressure and the unloading rate,the micro rupture surface gradually becomes smooth,the failure form of the rock gradually changes from the progressive failure to the sudden destruction,the rock is more prone to rockburst hazard.(3)The RFPA numerical simulation software was used to simulate the triaxial unloading test,the results show that:(a)During the unloading state,as the confining pressure decreasing the internal instability cells of rock gradually increasing from disorderly to orderly development,the micro cracks formed comes together to shape large scale macroscopic crack which eventually lead to the destroy of the rock.(b)Under the different initial confining pressure,the rock simulation mechanical characteristics results is relatively close to the test results.(c)At different unloading rates,the difference between the results obtained by numerical simulation and the indoor test are mainly reflected in the axial pressure and rock residual strength. |
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