Experimental and theoretical analysis of charge length on single-hole vibration amplitude from underground deep-hole blasting

Deep-hole blasting, characterized by large diameter and long charge length, is a prevalent practice in large-scale underground mining. However, the increasing charge length in each borehole, together with the growing charge weight, necessitates a heightened focus on the induced vibration effects. Understanding the impact of long charge length on induced vibration in comparison with traditional vibration characteristics is crucial for the safety control of deep-hole blasting. Therefore, experiments involving 6 charge lengths and 4 monitoring stations were conducted in an underground mine to clarify the variation of waveform and peak particle velocity (PPV). The entire borehole waveform superposed by the short charge elements was theoretically calculated and compared with the measured waveforms. The exact full-field model was further used to gain a comprehensive understanding of the effect of charge length and the related parameters of initiation positions and velocity of detonation (VoD). The experimental data and model analysis allow the following conclusions: (1) the effect of charge length on amplitude is highly dependent on the Mach wave, irrespective of varying initiation positions and VoDs; (2) an increase in the charge length does not necessarily lead to an increase of the PPV in the far-field, but it would result in a faster attenuation rate below a certain length; (3) given a constant charge weight, a greater length-to-diameter ratio of the explosive column results in a smaller vibration amplitude; (4) the appropriate duration of the explosive pressure should be considerably longer than the actual duration for investigating blast vibration.