Study on damage characteristics and acoustic emission Kaiser effect ofsandstone under cyclic loading and unloading conditions

In order to obtain the damage characteristics and Kaiser effect characteristics of sandstone under cyclic loading and unloading conditions, a series of tests on characteristics of acoustic emission(AE) have been performed on sandstone under different confining pressures.From the perspective of axial stress, the loading stress level and the energy dissipation damage, the variation of acoustic emission Felicity Ratio(FR) are studied under triaxial cyclic loading and unloading conditions.The reasonable judgment methods of rock Kaiser effect are evaluated under triaxial cyclic loading and unloading conditions.The results show that the dissipative energy damage parameters under cyclic loading and unloading can better reflect the progressive damage of rock failure under different confining pressure.Based on the calculation of dissipative energy damage parameters, it can better reflect the damage characteristics of different stages of rock and avoid the damage calculation of strain parameters and avoid the abnormal increase of damage value in the case of calculating damage using strain damage parameter.Evaluating acoustic emission (FR) can reflect the Kaiser effect of rock more accurately from aspects of the loading stress level and the energy damage.The stress of Kaiser effect failure increases with the increase of confining pressure.The acoustic emission (FR) decreases as the confining pressure increase under the same stress level and the same energy damage, and acoustic emission irreversibility becomes gradually blurry with the increase of confining pressure.