Dynamic response of rock mass subjected to blasting disturbance during tunnel shaft excavation: a field study

The blasting disturbance can damage the surrounding rock mass and then induce failures for underground rock engineering. Understanding the dynamic responses of the rock mass subjected to blasting disturbance is of great significance to maintain the stability and safety of underground rock engineering. This paper aims to reveal the dynamic responses of the surrounding rock mass subjected to blasting disturbance through a series of field blasting tests and propose prediction models for representative dynamic response parameters. The peak particle velocity (PPV), the dominant frequency (f(0)) of particle vibration and the peak strain rate (epsilon(m)) inside the rock mass under different blasting scenarios were recorded during the excavation of a tunnel ventilation shaft. The distributions of the PPV, f(0) and epsilon(m) were summarized based on the field observations firstly. The filed data indicated that PPV, f(0) and epsilon(m) decreased with the increase of the scaled distance (SD) in general. It is interesting to find that the higher strength of rock contributes to a stronger dynamic response. The prediction models of PPV in two types of weathered granite formations were proposed based on Ambraseys-Hendron model and regression analysis of field test data, and the prediction models of f(0) and epsilon(m) were established through dimensionless analysis and regression analysis. And the rationality of the prediction models proposed in this paper were verified through comparing with other existing or potential prediction models. Combining with the proposed prediction equations of PPV and damage degree division of rock mass based on PPV, the divisions of blast-induced damage zones in weathered granite stratum were also proposed, which are useful for preliminary predicting the damaged zones according to information of the construction site.