关键词: 露天矿山　, 延期时间　, 新增自由面假说　, 块度分布

Abstract: In open-pit mine step blasting,the reasonable setting of the delay time has a decisive impact on the blasting
effect. In order to solve the problems of reliability and high block rate of delay time calculation in blasting,the optimal range of
moving average velocity of blasting rock breakage is 11. 6~13. 6 m/ s based on energy conservation,and the calculation method
of "new free surface hypothesis" is optimized,and the influence mechanism of delay time on stress wave propagation,rock mass
damage evolution and post-explosion block distribution is systematically studied by combining numerical simulation and field
experiment. The results show that the delay time obtained by the model is in line with the physical process of the formation of
the new free surface,and the theoretical value is positively correlated with the measured data,and the coefficient of determination
R2 reaches 0. 927 3,which verifies the prediction reliability and universality of the model. Numerical simulations show that
the "relay style" crushing mechanism effectively promotes the formation of new free surfaces and the efficient utilization of energy,
and avoids the energy escape caused by the premature formation of the blasting funnel. The field experiment further shows
that the calculation model compensates for the energy dissipation caused by the short action time and significantly improves the
uniformity of the explosion stack. The research results provide a theoretical basis and technical support for the design of intelligent
blasting in open-pit mines.

Key words: open-pit mine,delay time,newly added free surface hypothesis,block size distribution