Blast Hole Raising Methods: Drop Raising

The Drop Raising method uses larger diameter and longer holes, relying on the Vertical Crater Retreat (VCR) concept, while the long-hole raising technique employs smaller diameter holes.

A spherical charge has a length-to-diameter ratio (L:D) of 1:4 or less, and up to 6:1.

Gravity and friction hinder crater formation in upward blasting but are beneficial in downward blasting, leading to a larger crater due to the removal of the ruptured zone.

<p>The stressed zone, with its elliptical shape, can lead to caving in of the material within the zone if not appropriately supported.</p> Signup and view all the answers

<p>Large diameter holes are blasted in an upward direction, retreating towards the top cut, creating a series of craters that effectively form the raise.</p> Signup and view all the answers

<p>A crater typically uses 5 holes: one central hole and four corner holes. The charge depth increases by 10-20cm from the central hole towards the corners.</p> Signup and view all the answers

<p>The charge length, $l$, is calculated by multiplying the big-blast-hole diameter, $d$, in mm by 6: $l = 6 \times d$.</p> Signup and view all the answers

<p>The optimal charge depth, $L_{opt}$, is half of the critical depth, $L_{crit}$: $L_{opt} = 0.5 \times L_{crit}$.</p> Signup and view all the answers

An advanced long-hole raising technique using larger diameter holes to drive raises.

A method where holes are blasted upward, retreating towards the top cut.

An explosive charge with a specific length-to-diameter ratio, crucial for crater formation.

The cavity created in rock by detonating a charge, influenced by charge direction.

The depth at which blasting becomes most effective and stable for crater formation.

50% of the critical depth, it maximizes effectiveness in blasting.

The area above the opening in rock, potentially caving in if unsupported.

The rule that charge length equals six times the diameter of the blast hole.