Blast damage zone strength reduction method for deep cavern excavation and its application

The drill and blast (D&B) method is widely used to excavate underground spaces, but explosions generally cause damage to the rock. Still, no blast simulation method can provide computational accuracy and efficiency. In this paper, a blast equivalent simulation method called the blast damage zone strength reduction (BDZSR) method is proposed. This method first calculates the range of the blast-induced damage zone (BDZ) by formulae, then reduces the strength and deformation parameters of the rock within the BDZ ahead of excavation, and finally calculates the excavation damage zone (EDZ) for the D&B method by numerical simulation. This method combines stress wave attenuation, rock damage criteria and stress path variation to derive the BDZ depth calculation formulae. The formulae consider the initial geo-stress, and the reliability is verified by numerical simulations. The calculation of BDZ depth with these formulae allows the corresponding numerical simulation to avoid the time-consuming dynamic calculation process, thus greatly enhancing the calculation efficiency. The method was applied to the excavation in Jinping Class II hydropower station to verify its feasibility. The results show that the BDZSR method can be applied to blast simulation of underground caverns and provide a new way to study blast-induced damage.