Study On The Acoutic Emisson Characteristics Duing Red Sandstone Creep Failuure Process Under Step Load And Unload Tests

The creep property is the inherent attribute of rock, and its one of the most important reasons causes rock failure. Currently, lots of researches focus on the rock deformation characteristics and the prediction methods of rock failue under dynamic load conditions. However, there are hardly any studies about the prediction method of rock failue under creep conditions. Hence, there will be of great significance to explore a prediction method of rock creep failure on the basic of the response characteristics during rock creep processes.The research mainly on deformation characterstics and acoustic emission (AE) characteristics of red sandstone during creep processes under load and unload tests, which is financially supported by Nation Science Foundation of China (No.51064010), han been done. In this paper, both of the axial and the lateral deformation characteristics and the AE characteristics during creep tests under different loading stress are firstly analysed. Then, a nonstationary nishihara viscoelasto-plastic rheological model is established, which can well reflects the characteristics of rock creep deformation. And also a prediction method of rock ceep failure is proposed. Finally, by introducing the parallel-bonded stress corrosion, the evolution characteristics of micro cracks during creep processes are analysed quantitatively.The results show that:(1) when the loading stress is less than or equall or greater than the long term strength of red sandstone, the sample will be in volume deformation state (during which the lateral creep deformation is not no significant), constant volume stage, and dilatancy stage (during which the lateral strain rate is greater than the axial strain rate), respectively. And the strain rate in steady creep stage is proportional to loading stress, while the comsume time that sample step into steady creep stage increases at an exponential function with loading stress increase. And the creep deformation can be illustrated by the nonstationary nishihara viscoelasto-plastic rheological model.(2) As for the AE tests, the AE ratio and the AE energy ratio decrease in the decelerated creep stage and steady creep stage, and their values and the reductions are related to the sample volume deformation. But their values become increasing in the middle-later stage of accelerated creep. In the volume deformation state, the AE amplitude and the AE b-value increase as creep time increasing, while the AE energy fractal dimension trends to a constant value eventually. In the constant volume stage and the dilatancy stage, both of the AE amplitude and AE b-value keep stable as creep time increasing, but the AE energy fractal dimension decrease.(3) When the sample just steps into the tertiary creep stage and befor sample failure, the AE amplitude takes on a transition phenomenon, and the AE dominant frequency increase from125kHz～156.25kHz to218.75kHz～250kHz. While the AE b-value and AE energy fractal dimension take on a declining trend, and then increases with time increasing, and finally declines again before the failure of the specimens in tertiary creep. Therefor, the AE characteristics above can be used as the prediction method of creep failure of red sandstone.(4) The AE phenomenon that happen during rock creep process is caused by micro cracks. In the creep tests, the sample failure is owing to tensile failure, and the shear crack appeared in the late tertiary creep stage, and also the numbers of cracks in creep tests are obvious more when compared with uniaxial compression tests. Acording to the discussions of the moment tensor, the potential failure surface of rock can be predicted by the moment magnitude. The numerical simulation results indicates that the confining pressure enhances the ductility property of sample, and the tension cracks decrease as the confining pressure increasing, but the shear cracks will increase as the confining pressure increasing, which emerge through the whole creep process.The results mentions above can provide some reference for the prediction of other types of rock creep failure, and have a certain application value.