Abstract: Nanfen Mine since hillside open pit into deep openpit,it is difficult to ditch.Especially in recent years,due to the influence of abundant groundwater,the borehole occurred serious collapse and the hole formation rate is low in the ditch blasting area.In order to solve this problem,professionals have carried on the exploratory research.And finally,the efficiency of hole formation increased from 0~30% to 100% through a series of experiments using guide sleeve of rolled iron plate.Nanfen mine has summed up a set of effective methods to improve the efficiency of hole formation,and this method has certain reference value for other similar projects.

Key words: Deep openpit,Trench perforation,Success rate