Transcript Blast Design - Supplemental Teaching Resources

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.
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
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
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
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
Other Formulas
• Formulas have the form
– V = K1 * [ Dist / (Ch) 0.5 ] K2
• Schemes try to make charge a function
–
–
–
–
V / K1 = [ Dist / (Ch) 0.5 ] K2
( V / K1 ) (1 / K2 ) = [ Dist / (Ch) 0.5]
Ch = { Dist / [ (V / K1) (1/K2)] } 2
Ch = ( Dist / K3 ) 2
• Coal Industry Regulatory Formula
– Ch = ( Dist / 60 ) 2
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 3.3 - Threshold for minor wet plaster
cracks
• 4.1 Plaster Cracks Expected
• 5.4 50% Prob Plaster Cracks and Falls Broken
Windows
• 7.6 50% Prob major damage - foundation and
bearing wall shifts
Fly Rock Problem