Abstract: There appears a lot of water in borehole with the pen pit deepening. The paper described the concept on open-pit water pressure pre-blasting by large-diameter vertical drilling, explored a set of techniques including a method to determine main blasting paramagnets, and the evaluation of water pressure pre-blasting, and the key technique of borehole charging and blasting hole stemming, and instant slope-forming by pre-split and cushion blasting. Through on-site application in Shouyun Iron Ore, a good effect with the ratio of vibration reduction of more than 65%, and backlash burst reduced by 38.5% was obtained. This technique can effectively improve the stability of the open-pit slope and lower slope maintenance costs. 

Key words: Water pressure pre-split, Cushion blasting, Large borehole, High slope