Abstract：In order to explore the breakage and damage effect problems of the underground protective engineering in rock under repeated penetration and explosion by precision guided weapons，the contrastive experiments of single-time drilled explosion and secondary drilled explosion have been accomplished. The experimental results show that the explosive crater diameters by secondary drilled explosion and single-time drilled explosion respectively are approximately equal，but the depth and the breaking range of explosive crater of the former is 2 times and 1.66 times of the later under equal total amount of charge. The measure results show that the peak pressures have a large difference at the same measuring points，and the peak pressures of the secondary drilled explosion are higher than those of the single-time drilled explosion for the same measuring points. The calculation results show that the pressure damped exponential of single-time drilled explosion is 1.933，and the stress wave velocity is approximately 4 800 m/s. The conclusions，which has been obtained by calculation according to the stress wave propagation mechanism，shows that the requested thickness of protective layer for secondary drilled explosion is 1.07 times of that for single-time drilled explosion under equal total amount of charge.
