Mining Geology, Mine Development and Surveying · Mine Development · 2 marks · Numerical answer
A blast round breaks 320000 m³ using 100 holes of diameter D=200 mm. Subgrade is 8D, stemming 25D and bench height 30 m. Powder factor is 3.2 m³/kg. Find explosive mass per unit charge length in kg/m, to two decimals.
Explosive mass per hole is 320000/(3.2×100)=1000 kg. Charge length is bench height plus subgrade minus stemming: 30+8×0.2−25×0.2=26.6 m. Thus mass per unit charged length is 1000/26.6=37.59398 kg/m, or 37.59 kg/m. Convert the diameter to metres before using its multiples.