Energy Evolution in Rockburst Model under Different Gradient Stress

To study the effects of different stress gradient on rockburst hazards, a novel experimental technique was proposed and a series of tests under different stress gradient paths were conducted on specimens (400 mm x 600 mm x 1000 mm) by using a true-triaxial gradient and hydraulic-pneumatic combined test device. The damage phenomena, force characteristics and acoustic emission (AE) signals of the specimen during rockbursts were systematically analyzed. The experimental results indicated that different stress gradient distributions not only affect the failure mechanism of the specimen, but also affect the energy conversion characteristics. With the stress gradient increasing from 0 to 6, the index r decreasing from 0.93 to 0.37, and the power law growth characteristics of the energy acceleration tends to be obvious. The energy released after rockburst accounts for 31.1%, 41%, 77.7%, and 87.5% of the total energy, respectively, which is an important reason for the severe damage tendency of rockburst. Rockburst intensity can be judged according to the stress/strength ratio corresponding to the inflection point of the AE energy fitting curve under different stress gradients, which can be used as an important precursor of rockburst.