Open Pit Blast Powder Factor Calculator
Drilling & blasting engineering: Calculate burden, spacing, subdrill, explosive mass per blast hole, and powder factor in kg/m³ and kg/tonne.
Bench Geometry & Drill Pattern
Charge & Powder Factor Output
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Frequently Asked Questions
What is the specific powder factor in mining engineering?
The powder factor is the ratio of explosive mass consumed to the volume or tonnage of rock fractured, expressed in kg/m³ or kg/tonne. Hard igneous rocks (e.g. granite, basalt) typically require 0.50 to 0.85 kg/m³, while soft sedimentary formations (shale, coal) require 0.20 to 0.40 kg/m³.
Why is the bench stiffness ratio (H/B) critical in blast design?
The stiffness ratio H/B compares bench height to burden. When H/B < 2.0, rock confinement resists lateral displacement, causing violent cratering, flyrock upwards, severe floor toe humps, and ground vibrations. An H/B between 2.5 and 4.0 allows efficient progressive flexural failure towards the free face.
What role does subdrilling (J) play at the bottom of the blast hole?
Subdrilling extends the blast hole below nominal pit bench grade (typically 0.2 to 0.3 times the burden) to ensure the bottom charge breaks floor rock cleanly at grade level. Without subdrilling, tensile stresses cannot overcome confinement at the toe, leaving high spots and rock humps that impede shovel loading.