Static-dynamic failure of truly 3D-compressed granite with a free face with natural fracture and the short-impending prediction

Static splitting failure typically serves as a faithful precursor to dynamic rockburst in deep hard rock engineering, which underlies the rockburst forecast. However, there is limited evaluation of the influences of natural fracture on rockburst development due to the scarcity of effective simulation experiments. To that end, true triaxial experiments with a free face with synchronous acoustic-optic-mechanics multi-physics field monitoring are conducted on the granite with single natural fracture, and the inclination angle and inherent roughness of natural fracture are the main considerations. Results show that the granite failure process involves calm stage, process zone nucleation stage, static splitting failure stage, and strength failure and post-peak softening stage. Typical delamination fracture in the intermediate principal stress direction is experimentally documented, as well as the rockburst for the configurations with smaller inclination angles and larger roughness. The triggering mechanism of rockburst is revealed as the shear off-induced instantaneous impact effect dictated by the large micro-asperities occupying the high stored energy. Moreover, the static-dynamic failure time of truly 3D (three-dimension)-compressed granite with a free face is quantitatively and accurately forecasted for the first time in both frameworks of the time-reversed Omori law (TROL)-based failure forecast model (FFM) and the long short-term memory (LSTM)-based FFM, which sheds light on the active control of rockburst in deep hard rock engineering.