The design of blasts for cast blasting in open-pit coal mining involves carefully optimizing several parameters to efficiently move overburden or rock into a designated area, like a decoaled pit, while protecting the coal seams. Key aspects of cast blast design include bench height, blast hole diameter, burden and spacing, explosive type and consumption, hole angle, and timing of detonations.
Key design parameters for cast blasting
- Bench height and mining panel width: these determine the volume of material to be cast, and the energy required.
- Blast hole drilling: large diameter holes (up to 12-ΒΌ inches or more) are typical, drilled to depths covering bench height plus subdrill.
- Burden and spacing: burden (distance from free face) and spacing between holes are critical and often based on hole diameter and rock properties. A common formula for burden is 25 to 40 times the hole diameter; spacing is typically 1.15 times the burden for an equilateral pattern.
- Explosive loading: charge length and powder factor (explosive mass per volume of rock) are calculated to ensure sufficient energy for breakage and casting.
- Hole angle: inclined holes (angled from vertical) are used to direct the blast energy towards the casting direction and optimize throw distance.
- Delay timing: millisecond delays between detonations control the blasting sequence and ensure effective throw while minimizing vibration and fly rock.
- Presplitting and smooth blasting: these techniques are used in conjunction with cast blasting to control the final profile and reduce damage to coal seams.
- Intelligent design tools: software solutions using ballistic theory and movement principles can optimize the pattern and parameters to minimize errors and maximize cast efficiency.
