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Vibration and Fly Rock ©Dr. B. C. Paul 2000 Note- The materials contained in these slides represent the author’s view of information commonly held in this subfield of Mining Engineering. Some information found in these slides can also be found in the 175 th Edition of the Blaster’s Handbook produced by DuPont.

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Vibration Constraints in Blast Design Need to determine how blast vibrations damage structures - and be able to measure it First impulse that it is magnitude of displacement is wrong - we move houses for miles Speed of shift seemed to correlate - but something doesn't work with distance - damage should go through the roof a close distance

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The Missing Piece Most Vibration Damage Occurs When blast vibration hits the natural oscillation frequency of the house Function of the Frequency - only recently had gages - hard to monitor Rocks damper the frequency - at close distance - frequency is high - buildings are low frequency - frequency drops at distance

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The Practical Regulatory Scheme Limit Peek Particle Velocity to Levels that would generally be acceptable even if you hit the natural frequency Three Approaches –Use a Standard Formula and check the design –Develop your own empirical formula –Monitor Every Shot

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Common Formulas Du Pont Formula –V = 160 * [ Dist /( Ch ) 0.5 ] -1.6 –V is peak particle velocity in inches/sec –Dist is distance from charge to protected structure or point of compliance –Ch is the charge fired on any one delay interval of 8 milliseconds of time The Term Dist/ (Ch ) 0.5 is sometimes called the Scaled Distance

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Other Formulas Formulas have the form –V = K 1 * [ Dist / (Ch) 0.5 ] K 2 Schemes try to make charge a function –V / K 1 = [ Dist / (Ch) 0.5 ] K 2 –( V / K 1 ) (1 / K 2 ) = [ Dist / (Ch) 0.5 ] –Ch = { Dist / [ (V / K 1 ) (1/K 2 )] } 2 –Ch = ( Dist / K3 ) 2 Coal Industry Regulatory Formula –Ch = ( Dist / 60 ) 2

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Damage Criteria 0.2 Inches/Sec - Humans Detect Motion 1 In/Sec - OSM Regulators Panic 2 In/Sec - Lowest Detected Threshold for trace damage under worst case 2.8 to Threshold for minor wet plaster cracks 4.1 Plaster Cracks Expected % Prob Plaster Cracks and Falls Broken Windows % Prob major damage - foundation and bearing wall shifts

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Fly Rock Problem

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