Study on high efficiency blasting technology of fractured rock mass in underground bauxite mine

The underground bauxite in Shanxi province is a thin ore body with gentle slope.The rock is hard but the mass is broken.The clay rock direct roof is greatly affected by blasting shock.The blasting efficiency is low and the advance of drilling footage is short that increases the safety risk of roof instability.Through the analysis of the unascertained measurement model, the blast-ability of bauxite rock mass is Ⅳ level.It provides support for the blasting design and the throwing scheme of vertical hole cutting.The technologies of vertical hole cut of deeper delayed projectile with central double cavity and smooth blasting are proposed.Through field blasting test, 3 m×2.5 m tunnel section with 2.1 m depth holes, mean effective penetration is > 1.85 m.Single footage length is increased by about 0.25 m.Specific charge is reduced from 0.73 kg/t to 0.6 kg/t.Two blasting holes are reduced in every single footage.The rock fragmentation is uniform and the roof is flat after blasting.