METHOD OF OPENCAST DRILLING AND BLASTING WORKS EXERCISING Russian patent published in 1994 - IPC

FIELD: mining industry. SUBSTANCE: first main boreholes 1 are drilled, using net scheme of 5 by 5 meters with redrill 2 for no more then 0.2 of the bench height. If the main boreholes 1 and auxiliary boreholes 3 are to be of identical diameter, then after the first row of boreholes 1 drilling is finished, boreholes 3 are being drilled in staggered order with the boreholes 3 depth of no more than half of the bench height. If the boreholes 3 diameter is to differ from main boreholes 1 diameter, then after all the main boreholes 1 having been drilled they begin to drill all the boreholes 3 at the angle of 75 -90 deg. to horizontal plane. Distance between boreholes 1 in the rows in the case is taken no more than half length of minimum resistance line and charges 4 for all boreholes are composed of parts with different brisance. Charges 4 in boreholes 3 are placed with partial covering of projection of upper part of charge 4 in boreholes 1. tamping 5 of the charges 4 is made by inert material with height of no less than 15 -20 diameters of borehole 1 or 3. Time interval of delay between the rows of boreholes 1 or 3 is increasing as distance of exploding row from the slant line of bench is growing. In the case diameter of borehole 3 is taken as 0.45 - 1.0 of borehole 1 diameter. It means, that diameters of boreholes 3 may be 125 or 167 mm in case boreholes 1 have diameters of 200 or 250 mm for СБШ-250 milling cutters. Boreholes 3 are located with eccentricity e , of crossing of diagonals of boreholes 1 for 0.03 - 0.05 of distance between the rows of boreholes 1. EFFECT: method is effective in open-cut mining. 3 cl, 2 dwg