Application of Hilbert-Huang transform based delay time identification in optimization of short millisecond blasting

The accurate identification of delay time in millisecond blasting plays an important role in the optimization of blasting design and reduction of vibration effect. Through a case study of a surge shaft blasting project, the capability of the EMD （empirical mode decomposition） method in identifying the delay time of short millisecond blasting with precise initiation was compared with the instantaneous energy method based on Hilbert-Huang transform （HHT）. The recognition rate of the EMD method was more than 80%, while the instantaneous energy method was less than 25%. By analyzing the instantaneous energy of single-hole blasting signal, it was found that the instantaneous energy method was adaptable to millisecond blasting with delay time longer than half of the energy peak period. The EMD method was used to identify delay time of millisecond blasting in Zijinshan open-pit mine. According to the identification results, the blasting parameters were optimized for controlling the blast-induced vibration and reducing the large block ratio. The field data showed that the velocity peak of ground vibration was reduced by more than 30%under almost the same maximum charge per delay by the optimization of delay time and detonating detonators. Combining with slag-remaining blasting and burden optimization of the first row, the large block ratio was reduced to less than 3%. The research results proved that the identification method based on HHT was feasible to optimize the blasting design. The identification method is also of certain reference value for design optimization of other similar blasting projects.

Influence of millisecond time,charge length and detonation velocity on blasting vibration

The law of blasting vibration caused by blasting in rock is very complex.Traditional numerical methods cannot well characterize all the influencing factors in the blasting process.The effects of millisecond time,charge length and detonation velocity on the blasting vibration are discussed by analyzing the characteristics of vibration wave generated by finite length cylindrical charge.It is found that in multi-hole millisecond blasting,blasting vibration superimpositions will occur several times within a certain distance from the explosion source due to the propagation velocity difference of P-wave and S-wave generated by a short column charge.These superimpositions will locally enlarge the peak velocity of blasting vibration particle.The magnitude and scope of the enlargement are closely related to the millisecond time.Meanwhile,the particle vibration displacement characteristics of rock under long cylindrical charge is analyzed.The results show that blasting vibration effect would no longer increase when the charge length increases to a certain extent.This indicates that the traditional simple calculation method using the maximum charge weight per delay interval to predict the effect of blasting vibration is unreasonable.Besides,the effect of detonation velocity on blasting vibration is only limited in a certain velocity range.When detonation velocity is greater than a certain value,the detonation velocity almost makes no impact on blasting vibration.

Vibration Superposition in Tunnel Blasting with Millisecond Delay

According to explosion dynamics and elastic wave theory, the models of particle vibration velocity for simultaneous blasting and milliseeond blasting are built. In the models, influential factors such as delay interval and charge quantity, are considered. The calculated vibration velocity is compared with the field test results, which shows that the theoretical values are close to the experimental ones. Meanwhile, the particle vibration velocity decreases quickly with time due to the damping of rock mass and has a harmonic motion, and the particle vibration velocity of millisecond blasting has short interval. The superposition of particle vibration velocities may reduce vibration because of wave interference, or magnify the surrounding rock response to the blastinginduced vibration.

Influence of delay interval on blasting efficiency of parallel hole cuts with an empty hole

Time interval of short delay ignition is an important factor to affect theefficiency of blasting cuts. The motion process of rock pieces in the cut cavity is analyzed, amechanical model to calculate the delay time of parallel hole cuts is presented for tunnel blasting,and a theoretical method to determine the volume ratio (the clearage rate) of the rock pieceswithin the cut cavity at different moments is proposed for the blasting cut with an empty hole.Numerical analysis results show that the optimal delay interval is proportional to the boreholedepth. The suggested results are of practical value to the optimal design of the delay interval inmillisecond blasting related to the parallel hole cuts with an empty hole.

Wavelet basis construction method based on separation blast vibration signal

As wavelet basis in wavelet analysis is neither arbitrary nor unique,the same signal dealing with different wavelet bases will generate different results.Therefore,how to construct a wavelet basis suitable for the characteristics of the analyzed signal and solve its algorithm and realization is a fundamental problem which perplexed many researchers.To solve these problems,in accordance with the basic features of the measured millisecond blast vibration signal,a new wavelet basis construction method based on the separation blast vibration signal is proposed,and the feasibility of this method is verified by comparing the practical effect of the newly constructed wavelet with other known wavelets in signal processing.