English：

The application of digital electronic detonators has enabled the implementation of hole-by-holeinitiation in underground engineering,which has been widely adopted. However, a unified understandingof the damage mechanism of rock mass under precise delay blasting has not yet been established.Focusing on the smooth blasting technique in tunnels, this study employs LS-DYNA to establish anumerical model of hole-by-hole initiation for breaking holes, analyzing the characteristics of damagedistribution on the tunnel cross-section. The results indicate that under simultaneous initiation, stresssuperposition between blast holes is significant, leading to through-going cracks along the line connectingthe holes. Under hole-by-hole initiation, the free surface plays a crucial role in crack formation. As theinter-hole delay time increases, the fractured area first increases and then decreases,with the bestfragmentation effect observed at delay times of 1ms and 3ms. The burden also has a notable influence onthe fragmentation effect. By defining a rock fragmentation ratio η, it is found that a larger burden resultsin a smaller η and lower rock-breaking efficiency.