Dynamic response of rock mass induced by the transient release of in-situ stress

During the excavation of rock mass with the method of drill and blast, the release of in-situ stress, also known as excavation load on boundary, is traditionally assumed as a quasi-static process, so the inertia and all other dynamic responses induced by the release of in-situ stress can be ignored. After analyzing the process of release of in-situ stress induced by rock mass excavation with the method of drill and blast and determining the duration of the release of in-situ stress, it is found that the release of in-situ stress induced strain rate can reach a magnitude of 10−1–101/s or higher if the initial in-situ stress has a level of 20–50 MPa, it implies that the release of in-situ stress is a transient process, and the transient character of the release of in-situ stress and correspondingly induced dynamic response of surrounding rock should be taken into account together with excavation. Problems such as the determination of redistributed in-situ stress corresponding to initiation sequences of millisecond delays, the way and path of the transient release of in-situ stress, transient release of in-situ stress induced vibration and comparison with blasting induced vibration are also discussed in this paper. Finally, a case of in-situ stress release induced vibration in Pubugou hydropower projects are presented as verifications.

► Releasing process of in-situ stress during deep rock blasting is discussed.
► In-situ stress is released with 2–5 ms in the blasts of most deep-buried tunnels.
► Transient release of in-situ stress induced dynamic responses should be considered.
► Numerical simulation is conducted to demonstrate the presented theory.