Evaluation of Rock Vibration Generated in Blasting Excavation of Deep-buried Tunnels

Abstract

The experimental tunnels of the China Jinping Underground Laboratory are constructed in a maximum overburden depth of 2375 m and subjected to extremely high in situ stress more than 50 MPa. When these deep-buried tunnels are excavated with the method of drill and blast, the surfaces created by blasting are generated almost instantaneously, and thus the initial stress on these surfaces is also suddenly released. This transient release of in situ stress causes elastic waves to propagate in rock masses and may have an important effect on the subsequent rock vibration. In this study, a three-dimensional FEM modeling in combination with site investigation is conducted to research the Peak Particle Velocity (PPV) attenuation and frequency characteristics for the rock vibration induced by transient stress release and its combined actions with blast loading. The results indicate that the transient release of the high stress generates considerable vibration velocity that is comparable to that of blast loading. It is not a negligible excitation for the rock vibration generated in blasting excavation of deep-buried tunnels. Furthermore, the vibration induced by transient stress release has much lower frequency than that caused by blast loading. This causes the unloading vibration to decay more slowly and become the major vibration component at far distances. Also, the effect of transient stress release is found to enhance intensity of the total vibration and furthermore cause an increase in its low-frequency content. On the basis of this, the allowable charge amount per delay and the minimum safety distance are finally discussed with a special emphasis on the contributions of the transient stress release to the total vibration.