Abstract: To study the influence of different air gaps on the damage of rock at the bottom of the blast holes,a cylindrical
concrete model with a size of ϕ400 mm×400 mm was cast using a steel mold. Blast simulation experiments were conducted by
setting different lengths of bottom air gaps. The longitudinal wave velocity of the model before and after blasting was measured
using a non-metallic ultrasonic detector to reflect its integrity and the degree of internal damage;at the same time,the strain
changes during the blasting process were tested using an ultra-dynamic strain gauge. Additionally,numerical simulation analysis
of the rock damage at the bottom of the blast holes under different air gap lengths and explosive structures was carried out using
the ANSYS/ LS-DYNA finite element software. The simulation results were in good agreement with the experimental data. The
results show that the air gap in the blast hole plays a buffering role during the propagation of the explosion shock wave,which
can effectively reduce the damage of the rock at the bottom of the blast hole and protect the underlying rock mass. However,an
excessively long air gap will reduce the utilization rate of blasting energy and affect the blasting effect. Based on the combined
analysis of experiments and simulations,when the air gap length is set at 20 mm,it is possible to effectively control the damage
at the bottom while ensuring good blasting efficiency.

Key words: air interval,concrete model,rock damage,blast test,numerical simulation