Abstract: Reasonable selection of the delay time of induced caving blasting in the goaf roof can effectively improve the effect of induced caving. In order to determine the optimal delay time of millisecond delay blasting in goaf， after analyzing the technical principle of induced caving， using the delay time as the starting point， combined with the actual situation of an underground mine， a numerical simulation model of induced caving blasting was established. Using the LS-DYNA finite element analysis software to simulate the explosion process with delay time of 20 ms， 35 ms and 50 ms respectively， the stress cloud diagram of the explosion process and the curve of the effective stress of each observation point with time are obtained. The simulation results show that the minimum stress and maximum value of the central part of the roof is affected by the blasting delay time， and the corresponding delay time was 35 ms when the maximum effective stress at both ends of the roof was the lowest. When judging by the proximity between the maximum effective stress and the compressive strength of ore and rock， it was concluded that the induction effect is the best when the delay blasting time between presplitting blasting and roof caving blasting was 20 ms.By comparing and analyzing the change of effective stress at each observation point， it is determined that the effect of induced caving is the best when the delay time is 20 ms. The study results can provide a reference for the optimization of blasting parameters in mines by adopting induced caving method.

Key words: underground mining, inducement dilapidation, effective stress, compressive strength, delay time, numerical simulation