Abstract: Through the acoustic emission monitoring on two loading modes i.e. Brazilian splitting and uniaxial compression of limestone, the b-value characteristics of rock rupture and the impact factors are discussed. The results show that cumulative calculation of b-value has a high fitting degree and small error. When the step length is 5 dB, the overall change trend of b-value with time under different threshold values is similar. It shows that the calculation of b-value is more reasonable with the step length of 5 dB and threshold value of 40 dB, which can reduce the influence of non-rock fracture signals on the variation of b-value. Additionally, based on the fluctuation characteristics of the dynamic b-value, it can be seen that under the splitting load, the damage evolution of limestone can be divided into three stages: (0-40%)?c, (40%-90%)?c, and (90%-100%)?c. Under uniaxial compression load, the damage evolution of limestone can be divided into two stages: (0-80%)?c and (80%-100%)?c (?c is the peak strength). At different stages of rock damage, it presents different levels of damage in the rocks. In the crack propagation stage, compared with uniaxial compression load, the dynamic b-value increases steadily during crack growth process under Brazilian splitting load condition, and the dynamic b-value fluctuates greatly during the whole failure process. Through the experiments in this paper, it shows that the variation of b-value depends on the structural property and failure modes of the limestone fracture surface.

Key words: rock acoustic emission, b-value, uniaxial compression, Brazilian splitting, impact factors