Time-delayed Failure Process of Granite and Its Energy Evolution and Acoustic Emission Characteristics

Time-delayed rockbursts during underground engineering construction seriously endangered the engineering safety. In this paper, an experiment of rock time-delayed failure is designed and conducted, and the associated energy evolution laws and acoustic emission (AE) characteristics were analyzed. There is an obvious time effect of granite time-delayed failure under true triaxial conditions. There are two calm periods in granite time-delayed failure process. The failure modes can be divided into two categories, i.e., time-delayed failure I and time-delayed failure II. In the load maintenance stage, the total energy continues to increase, the elastic strain energy didn't change significantly, and the dissipated strain energy increases rapidly. For time-delayed failure I, when the AE hits rises sharply, it reached its maximum subsequently, and the first small peak of absolute energy appeared. On the eve of the rockburst, the AE hits began to rise gradually, and the absolute energy was with a small protrusion. For time-delayed failure II, when the AE hits rises rapidly, it reached a high level. The small peak of absolute energy appeared. In the eve of the rockburst, the hits showed a steep increase trend and reached its maximum, the absolute energy also presented a rapid rise trend. The research results have certain reference value for the early warning and control of the time-delayed rockbursts in underground engineering.