Experimental Study Of Remotely Triggered Rockburst Induced By Tunnel Axial Dynamic Disturbance Under True-Triaixal Condition

Rockburst is a kind of dynamic ejection failure of the surrounding rock mass under high stress region during the underground excavation. According to the triggering mechanism, the rockburst can be divided into self-initiated rockburst and remotely triggered rockburst. Remotely triggered rockburst is characterized by dynamic failure of the rock mass near the excavated boundary in a static high stress equilibrium condition after stress redistribution in excavation process, induced by dynamic disturbance, such as explosion, vibration, stress impact from neighboring rockbursts, earthquakes etc. Generally, it often can be seen that the rockburst is triggered by the dynamic disturbance (blasting) near the tunnel face spreading in tunnel axis direction. As its high randomness in space and time, such a rockburst cannot be predicted or forecasted accurately, leading to seriously engineering accident and economy loss easily.Therefore, for sake of a deep understanding of the remotely triggered rockburst, the pregnant process of remotely triggered rockburst was mimicked successfully based on the experiment test on granite rock specimen using a novel true-triaxial test machine. A new loading path of keeping one free face, loading on other free faces static and applying dynamic disturbance on one face is also used. And the influences of tangential stress, axis stress, radial stress, amplitude and frequency of the dynamic disturbance on rockburst are also investigated. During the test, high speed camera system, dynamic image analysis software and deformation monitor system are used to record and analysis the experimental results including failure modes, rockburst process, duration time, stress, strain, size distribution of the fragments, damage of the tested specimen and the kinetic energy etc.. Additionally, the energy evolution of the remotely triggered rockburst is also discussed. The experimental results show that:1. It indicates that the enough large Z-direction stress, the dynamic disturbance amplitude and frequency are the three basic requirements for the remotely triggered rockburst induced by the tunnel axis dynamic disturbance. It also can be seen that with the increasing of the static Z-direction stress, the dynamic disturbance amplitude or frequency when other load parameters are kept constant, the duration time of the rockburst pregnant and dynamic disturbance decreases, the Z-direction strain from dynamic disturbance starting to rockburst decreases, the kinetic energy of the ejected fragments increases, the damage of the tested specimen gets more seriously, and the breakage of the fragments becomes slighter. Overall, the higher the Z-direction stress, the dynamic disturbance amplitude or frequency is, the easier the rockburst is triggered.2. It is clear that the static X-direction stress have a significant influence on the remotely triggered rockburst. It can be seen that with the increasing of the static X-direction stress, below 50MPa, when other load parameters are kept constant, the carry capacity of the tested specimens increases, the duration time of the rockburst pregnant and dynamic disturbance increases, the Z-direction strain from dynamic disturbance starting to rockburst increases, the kinetic energy of the ejected fragments decreases, the damage of the tested specimen becomes slighter, and the breakage of the fragments gets more seriously. Overall, the higher the X-direction stress is, the more difficult the rockburst is triggered.3. It is clear that the static Y-direction stress have a significant influence on the remotely triggered rockburst. It can be seen that with the increasing of the static Y-direction stress, below 10MPa, when other load parameters are kept constant, the carry capacity of the tested specimens increases, the duration time of the dynamic disturbance increases, the kinetic energy of the ejected fragments decreases, the damage of the tested specimen becomes slighter. It also can be seen than the Y-direction stress has no obviously relation with the duration time of the rockburst pregnant, the Z-direction strain from dynamic disturbance starting to rockburst increases, and the breakage of the fragments. Overall, the higher the Y-direction stress is, the more difficult the rockburst is triggered.4. The remotely triggered rockburst can described into four stage, particles ejection, rock material being split into rock plate, rock plate expanding and bending, and fragment ejection as soon as rock plate breaking off.5. It is found that the dynamic damage shows a trend of fast increasing, gradual growing and sharply increasing during the dynamic disturbance process. With the increasing of the damages, the limited energy restored capacity of the rock mass declines. When the elastic strain energy is larger than the limited energy restored capacity during the final failure, parts of the residual elastic energy will be transmitted into kinetic energy of the fragments, leading to the rockburst.