Time-frequency Analysis Of Blasting Vibration Effect Of Free Surface

Blasting technology is playing a more and more important role in the engineering construction,and research on the influence factors of blasting vibration control gets more attention,the free surfaces have great influence to blasting effect and blasting vibration control.In combination with the measured data of blasting vibration,the influence of the number of free surface on the blasting vibration effect is analyzed.When blasting seismic waves propagate to the free surface,the compressive stress wave is reflected as the tensile stress wave.When the free surface is increased,the stress wave is reflected more tensile stress wave in the interface,and the complex mutual interference,obviously can improve the blasting effect.The total energy,the frequency band energy and the PPV of each band of blasting vibration signal with different number of free surface are obtained by using wavelet analysis method.Then the energy distribution characteristics of blasting vibration signal with different number of free surface are studied.The results show that because of a single free suiface in slotted blasting or cut blasting,most of the energy of the explosion will be consumed as seismic energy;the more free surface,the less the total energy of blasting vibration signal.With the increase of the number of free surface,the distribution of the vibration components of each frequency band can be affected,which makes the blasting energy more tend to be the high frequency distribution,so that the energy in the middle and low frequency can be reduced,and the vibration velocity is reduced as well.Under the condition of different free surface,the PPV of high frequency band is higher than that of the low frequency band,but the duration of the vibration is the shortest,and the energy attenuation is fast in the same vibration signal,though there’re a lot of high frequency energy in the near-blasting field,the attenuation is faster,while the attenuation is slower in the far field.Analysis the measured data of blasting vibration.Regression analysis and wavelet analysis can get that the blasting vibration intensity decreases with the increase of free surface.However wavelet analysis can consider more the influence of blasting vibration,for instance energy and frequency.