Mining Geology, Mine Development and Surveying · Mine Development · 2 marks · Numerical answer
A surface blast has spacing 4 m, burden 3 m, hole diameter 110 mm and drilled length 8.8 m including 10% subgrade. Explosive density is 900 kg/m³ and powder factor is 2.5 m³/kg. Find charge length in metres, to two decimals.
The drilled length equals 1.10 times bench height, so H=8.8/1.1=8 m. Rock volume per hole is 4×3×8=96 m³, requiring explosive mass 96/2.5=38.4 kg. Linear charge mass is 900×π×0.110²/4=8.55299 kg/m. Charge length is 38.4/8.55299=4.48966 m, or 4.49 m. Subgrade is excluded from the production bench volume.
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