Study On Near-Field Vibration Spectrum Characteristics Of Single-Hole Blasting At Different Initiation Positions

In the construction of hydroelectric engineering,mining and municipal infrastructure,blasting,as a highly efficient and economical construction technology,inevitably produces some negative effects,and blasting vibration is the first one to hit.With more and more stringent control over blasting vibration,it is difficult to meet the requirements only by using the peak value of blasting vibration speed as the criterion.Therefore,the two-factor safety criterion based on the peak value of blasting vibration speed and vibration frequency gradually becomes the mainstream.It is of great significance to study the amplitude spectrum characteristics of different initiation positions for more effective control of blasting vibration hazards.In this paper,a systematic study is carried out on the distribution characteristics of nearfield amplitude spectrum at different blasting positions by combining theoretical analysis with engineering verification.The peak particle vibration velocity and Fourier principal frequency formulas at different initiation positions are derived to reveal the distribution law and influence mechanism of initiation position on near-field amplitude spectrum,and to analyze the influence of different blasting parameters on peak particle vibration velocity and vibration frequency.The amplitude spectrum characteristics of the initiation position have been verified by field tests.The main research results are as follows:(1)Based on the solution model of Heelan equivalent unit short column,analytical formulas for different initiation positions of long column charge are derived.Through the calculation of one-dimensional flow model,it is found that the position of initiation in the hole regulates the distribution of blasting vibration field,and the positive superposition of propagation along the detonation wave increases.The research shows that the peak vibration velocity of particle initiated at two points is the highest,followed by bottom and middle point of hole and minimum of orifice.(2)The study found that a change in the location of the initiation point shortens the propagation path of the blast wave in the hole,which in turn leads to a reduction in the load rise time.Through the study of the energy transfer mechanism of the double-point detonation,it was found that the double-point detonation shock wave collision interface blast wave enhancement and thus improve the rock breaking effect and blast vibration amplitude spectrum.(3)By introducing the concept of amplitude decay term,the relationship between the amplitude decay term and the detonation location and frequency was established.The study shows that the main frequency decay law in the near zone: double point detonation > mid-point detonation > bottom of the hole detonation > hole detonation,in the far zone with the increase in the distance between the burst center,the main frequency of different detonation location differences are small,but sudden changes occur at a specific burst center distance.And the use of mass center frequency calculation found that different detonation location with the distance of the decay uniformly without sudden changes in the location of the detonation generated by the frequency difference in contrast is obvious,centroid frequency the decay law: double point detonation > detonation in the point of detonation > bottom of the hole detonation > hole detonation.(4)Comparative analysis was conducted on the influencing factors of peak particle vibration velocity and centroid frequency.Research has found that the peak vibration velocity of particles is directly proportional to the amplitude of the explosive load and the length of the charge,and inversely proportional to the duration and rise time of the load.As the distance between the detonation centers increases,the influence of the initiation position on the peak vibration velocity of the particle gradually decreases.The frequency of the centroid is directly proportional to the rock parameters,and inversely proportional to the load duration,load rise time,and charge length.An increase in the amplitude of the blasting load does not cause a change in frequency.(5)In this paper,the vibration frequency and PPV comparison analysis of the field experimental data of Dawangtang limestone quarry,Fengning pumped storage power station and Baihetan hydropower station,the vibration frequency has the following regulations: twopoint initiation > mid-point initiation > bottom initiation > top initiation,and PPV has the following regulations: two-point initiation > bottom initiation > mid-point initiation >top initiation.