Blast Hole Raising Method - Drop Raising
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Questions and Answers

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?

  • 1:4 or less (correct)
  • 6:1
  • 4:1
  • 1:1
  • 10:1

    • 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?

    <p>To create a larger crater for efficient material removal. (C)</p> Signup and view all the answers

    What is the formula used to calculate the charge length in Drop Raising?

    <p>Charge Length ($l$) = 6 $ imes$ d (B)</p> Signup and view all the answers

    How many holes are typically used in a single crater formation, according to the text?

    <p>5 (A)</p> Signup and view all the answers

    What is the minimum charge depth difference between the holes in a crater formation?

    <p>10 cm (C)</p> Signup and view all the answers

    Which of the following is NOT a feature of the Drop Raising method?

    <p>Requires high-precision drilling technology (D)</p> Signup and view all the answers

    Flashcards

    Drop Raising

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

    Vertical Crater Retreat (VCR)

    A concept involving creating surface cavities by detonating explosives vertically.

    Crater

    A surface cavity created by detonating an explosive charge in rock.

    Explosive Charge Shape

    Charges are often spherical or geometrically equivalent and impact crater formation.

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    Length-to-Diameter Ratio (L:D)

    The ratio describing the relation between charge length and diameter for effective blasting.

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    Charge Depth Formula

    The formula to calculate charge depth based on hole diameter; $Charge Length (l) = 6 \times d$.

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    Cavity Equilibrium

    The stability condition of a rock mass around a created crater affecting size and stability.

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    Blasting Operations in Raises

    Carrying out blasting with large diameters in vertical or steeply inclined holes.

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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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    Description

    This quiz covers the drop raising method in blasting techniques, focusing on its principles, applications, and the mechanics involved in creating raises using explosive charges. You'll explore key factors influencing crater size and the effects of rock properties. Understanding this method is essential for applications in both surface and underground blasting.

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