Podcast
Questions and Answers
What does the term 'crater' refer to in blasting terminology?
What does the term 'crater' refer to in blasting terminology?
- A surface cavity created by detonating explosives (correct)
- The area surrounding a blast hole after detonation
- A specific type of explosive charge used in underground mining
- A technique used to raise the roof of an underground mine
What is the typical length-to-diameter (L:D) ratio of a spherical charge used in blasting practice?
What is the typical length-to-diameter (L:D) ratio of a spherical charge used in blasting practice?
- 1:4 or less (correct)
- 6:1
- 4:1
- 1:1
- 10:1
How does gravity affect crater formation in underground mining?
How does gravity affect crater formation in underground mining?
- Gravity causes the crater to expand horizontally.
- Gravity increases the pressure within the crater.
- Gravity has no significant impact on crater formation.
- Gravity pulls the ruptured zone downwards, increasing the crater size. (correct)
What is the primary reason for using large diameter holes in the Drop Raising method?
What is the primary reason for using large diameter holes in the Drop Raising method?
What is the formula used to calculate the charge length in Drop Raising?
What is the formula used to calculate the charge length in Drop Raising?
How many holes are typically used in a single crater formation, according to the text?
How many holes are typically used in a single crater formation, according to the text?
What is the minimum charge depth difference between the holes in a crater formation?
What is the minimum charge depth difference between the holes in a crater formation?
Which of the following is NOT a feature of the Drop Raising method?
Which of the following is NOT a feature of the Drop Raising method?
Flashcards
Drop Raising
Drop Raising
An advanced long-hole raising technique using larger diameter holes.
Vertical Crater Retreat (VCR)
Vertical Crater Retreat (VCR)
A concept involving creating surface cavities by detonating explosives vertically.
Crater
Crater
A surface cavity created by detonating an explosive charge in rock.
Explosive Charge Shape
Explosive Charge Shape
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Length-to-Diameter Ratio (L:D)
Length-to-Diameter Ratio (L:D)
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Charge Depth Formula
Charge Depth Formula
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Cavity Equilibrium
Cavity Equilibrium
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Blasting Operations in Raises
Blasting Operations in Raises
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Study Notes
Blast Hole Raising Method - Drop Raising
- Drop raising uses long holes and large diameters to create raises
- This technique is based on the vertical crater retreat (VCR) concept
- VCR involves creating a surface cavity in rock using explosive charges
- Initially used for surface blasting, now used for underground blasting
- Spherical or equivalent geometric charges are used; ratio of length to diameter (L:D) is 1:4 or less, up to 6:1
- Crater size influenced by gravity, friction and rock properties
- Gravity enlarges the crater by removing the ruptured zone
- Stressed zone of elliptical shape formed above the opening after excavation
- Rock properties and structural geology affects total height of the cavity
- Cratering characteristics of rock mass are studied for blasting to vertical or steeply inclined holes
- Crater depth increases from 10-20 cm between blast holes
- Charge length (l) is calculated as 6 times the diameter (d) of the blast hole (l = 6xd)
Crater Theory
- A crater consists of five holes; one central, four at the corners
- Crater theory is valid for the central hole
- Charge depth for peripheral holes increases from 10-20cm between each hole (fig 13.9(b))
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