Abstract: Based on the measured single deck blast vibration signals, time frequency characteristics were analyzed of the superposition signal of the single deck signals with various features by MATLAB programming, and, through introducing the concept of amplitude reduction ratio and vibration velocity ratio, the variation law of characteristics of the superposition signal in millisecond blasting with the delay time, detonating sequence and properties of the seed-signal is put forward. It is found that time difference of the superposition signal arriving at a certain amplitude reduction ratio is not a specific moveout point but many intermittent time difference sections. Meanwhile, dominant frequency variates in a step sawtooth pattern with the difference of the delay time. Under rational millisecond time, the more similar the vibration characteristics of two seed-signals are, the more evident the interference vibration reduction effect is. If charge weight is designated, vibration reduction effect is much better when the segment with small charge quantity is detonated prior to others. And the measured test data in site reflect that the research results basically accord with the practical operation laws of millisecond blasting.

Key words: blasting vibration, waveform superposition, millisecond time, time frequency characteristics, interference vibration reduction, blasting