Reasonable axial length of an air column can lead to crack penetration between adjacent blast holes without generating crushed zone on hole wall, which plays an important role in presplit blasting. The variation characteristics of initial impact pressure on the hole wall along the axial direction of blast hole were analyzed by theoretical calculation. For the blasting engineering of Barun Open-pit Mine, a reasonable axial length of air column for presplit blasting was preliminarily estimated to be about 1.5 m, and then the variation of stress after blasting with different axial lengths of air column was analyzed by numerical simulation. The results show that the initial pressure on the hole wall in the air column section presents a "U-shaped" distribution along the axis of blast holes, and the minimum pressure exists at the middle of the air column. When the axial length of an air column is 1.5-2.0 m, the numerical simulated stress oscillates when it drops to about 10 MPa, which can meet the requirements of crack initiation and propagation between rock holes. The engineering practice in the stope of Barun mine shows that when the air column length is 1.5 m, the slope roughness after presplit blasting is less than 10 cm, the half-hole mark rate greater than 85% and the resultant velocity of blasting vibration is 5.782 cm/s, presenting excellent indicators.

presplit blasting  /  numerical simulation  /  air column length  /  impact pressure  /  blasting vibration  /  decoupling charge  /  crack penetration  /  roughness  /  hole mark rate  /  blasting vibration