Effect of the propagation direction of the weak dynamic disturbance on rock failure: an experimental study

Weak dynamic disturbance caused by drilling and blasting, adjacent rockburst, and machine vibration is a key factor to rock failure/rockburst during underground excavation. Meanwhile, the propagation direction of weak dynamic disturbances varies when different underground constructions are encountered. To investigate the effect of the propagation direction of the weak dynamic disturbance on rock failure, a general true triaxial test (applying a loading state of “six stressed faces”) and a modified true triaxial test (applying a loading state of “one free face and five stressed faces”) are conducted. For the former test, P_d1 (weak dynamic disturbance along the direction of σ₁), P_d2 (weak dynamic disturbance along the direction of σ₂), and P_d3 (weak dynamic disturbance along the direction of σ₃) are involved. For the latter test, only P_d1 and P_d2 are involved due to the limitation of the testing machine used. After testing, the rock strength and macroscopic failure characteristics of the tested specimens are systematically investigated. The experimental results indicate that the rock strength of the tested specimen without weak dynamic disturbance is higher than those with weak dynamic disturbance, indicating a reduction effect of the weak dynamic disturbance on the rock strength. P_d3 has the greatest reduction effect on rock strength due to its greatest promotion effect on crack development, while the reduction effect of P_d1 on rock strength, as well as its promotion effect on crack development, is smallest. In addition, for the tested specimens with a free face, the failure process is observed and investigated. Rockburst characterized by rock fragment ejection occurs during the testing process of these specimens. The kinetic energy of the ejected blocks without weak dynamic disturbance is higher than that with weak dynamic disturbance, showing that the weak dynamic disturbance has a reduction effect on kinetic energy. In addition, the kinetic energy of ejected blocks is lower under the P_d2 condition than that under the P_d1 condition; consequently, P_d2 has a greater influence on the kinetic energy of the ejected blocks, i.e., the intensity of rockburst.