Rock damage control in bedrock blasting excavation for a nuclear power plant

Drill and blast is a major method for bedrock excavation in nuclear power plant engineering. Under blasting excavation, blast-induced vibration propagates in rock mass and induces damage to surrounding rock. Studying the characteristics of wave propagation and blast-induced damage to rock mass is most important to restrict the damage extension. In the present paper, in support of the bedrock blasting excavation for the Linao Nuclear Power Plant project (LNPP), the site seismic survey and sonic wave test are presented to study the characteristics of wave propagation and the blast-induced damage for rock mass. The explosive load, rock damage characteristics and peak particle velocity (PPV) attenuation law are also investigated by numerical simulation using commercial software. It can be seen that the numerical simulation results agree well with that obtained by site monitoring. Based on the site monitoring and the numerical simulation, the relationship between PPV at 30 m away from the charge hole and the damage depth of rock mass is established. A simple method based on safety threshold of vibration velocity for rock mass to restrict the damage depth of rock mass under blasting excavation is presented. According to the damage controlled method and the presented safety threshold of vibration velocity for rock mass, the remained bedrock can be simply and effectively protected during blasting excavation.