Influence of void ratio on 'Blast Pull' for different confinement factors of development headings in underground metalliferous mines

摘要

Development headings such as adits, ramps, haulages, cross-cuts, ore drives and exploratory drives are the important structures of any underground metalliferous mines. Drilling and blasting is the most preferred excavation method used to create such drivages for extracting mineral deposits, since the progress rate of drivages impacts the overall productivity of mines. There are many controllable blast design parameters and uncontrollable geological-geotechnical parameters influencing the blast pull (i.e. advancement factor). This paper investigates the influence of void ratio (i.e. the ratio between total area of empty holes and cut area of a first shot hole) on blast pull for development faces having different confinement factors. The confinement factor is defined as the ratio of drill hole length and cross-sectional area of development headings. For this study, field investigations were performed in four lead-zinc mines. Thereafter, experimental blasts were conducted in haulage drives on the footwall side, ore drives and exploratory drives on the hanging wall side, for different confinement factors ranging from 0.10 to 0.37. Several parallel hole cut designs were experimented upon, with the void ratios varying from 19.80% to 75%. Results revealed that the void ratio plays an important role in the advancement factor of development headings. Furthermore, with an increasing confinement factor, the void ratio should be kept high for achieving maximum blast pull. Statistical analysis was carried out to establish trends between the void ratio and the confinement factor of development faces using accuracy indicators of MAPE, MAD and MSD. Eventually, a relationship was established for the effective parallel hole cut designs to achieve more than 90% advancement factor.