Statistical characteristics of sandstone acoustic emission under triaxial unloading confining pressure

In order to thoroughly explore the internal response characteristics and the catastrophic behaviors of rock mass caused by unloading in deep excavation process,the self-developed triaxial acoustic emission acquisition system is used to conduct the triaxial unloading tests of sandstone with different unloading rates and different confining pres-sures. Seismic statistics method is used to analyze the parameters such as absolute energy E and waiting time δ. The re-sults show that:① the probability density function of absolute energy released in the unloading follows a power law dis-tribution well in the range of 101 aJ to 104 aJ. ② With the decrease of unloading rate,the possibility of small energy events occurrence is increasing. There is a similar trend with the increase of confining pressure in the same unloading rate. ③ The “ after-shock” of acoustic emission events meets the same linear relationship under different confining pressures and unloading rates,and it is not affected by the fluctuation of the “ main shock” events energies. ④ In a short time interval range (less than 0. 1 s),the power exponent is not affected by confining pressure and unloading rate. For a long interval range (greater than 0. 1 s),the power exponent fluctuates in the range of 1. 3 to 1. 9. The dis-tributions of waiting time for different energy thresholds show universality well.