vibrations from blasting where is blasting used? mining construction – demolition – new...
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Vibrations from blastingVibrations from blasting
Where is blasting used?MiningConstruction
– Demolition– New constructions– Densification
Kim André Larsen •Ph.D.Student• Department of Civil Engineering
Vibrations from blastingVibrations from blastingDisturbance from blasting
Kim André Larsen •Ph.D.Student• Department of Civil Engineering
Vibrations Air blast (Low frequency air vibration) Fly rocks
Vibrations from blastingVibrations from blasting
Parameters which affect vibration characteristics In practically the same ones which influence the results of
the blasts. The surrounding geology and rock mechanics
– In homogenous and massive rock masses the vibrations are propagated in all directions, but not in complex geological structures.
Thickness of soil overlaying rock. – Magnitude of the vibrations decrease rapidly with distance
increase if soil overburden is present.– Large energy is used up in overcoming friction between particles
and in displacing them.
Kim André Larsen •Ph.D.Student• Department of Civil Engineering
Vibrations from blastingVibrations from blasting
Parameters which affect vibration characteristics Distance from the blast. The earth acts as a filter
through which the lower frequencies pass. At long distances the ground vibrations will have more energy in the low frequency range.
Powder factor– More or less explosive can both give increased
vibrations
Kim André Larsen •Ph.D.Student• Department of Civil Engineering
Vibrations from blastingVibrations from blasting
Parameters which affect vibration characteristics Delay period Distance between blast holes Blast hole diameter Blast hole depth Distance from blast hole to free edge Blast hole inclination
Kim André Larsen •Ph.D.Student• Department of Civil Engineering
Vibrations from blastingVibrations from blasting
Frequencies from blasting Blasting in coal mines
– Frequency between 4 and 12 Hz is very well propagated.
– 90% of the blasts produces frequencies under 20Hz
Construction blasting– Creates higher frequencies with the most often
happening at abaout 35-40 Hz
Kim André Larsen •Ph.D.Student• Department of Civil Engineering
Vibrations from blastingVibrations from blasting
Seismic waves from blasting Wave front is displaced radially from the point of
detonation Rock blasts usually gives
– Rayleigh waves – Love waves
Love waves are faster then Rayleigh (1.73)
Kim André Larsen •Ph.D.Student• Department of Civil Engineering
Vibrations from blastingVibrations from blasting
Seismic waves from blasting Love waves: Particle motion is transvers to that of
propagation Rayleigh waves: Eliptical particle orbit, usually a motion
that is contrary to the propagation direction The Rayleigh wave carries about 70-80% of the total
engergy, and dominates the surface ground movement at several hundred meters from the blast
Kim André Larsen •Ph.D.Student• Department of Civil Engineering
Vibrations from blastingVibrations from blasting
Measuring Blasts with delay gives a complex interaction in
both time and space because of the different velocities in which the waves travels.
Measuring must therefore be performed in three directions. Radial, vertical and transversal.
Kim André Larsen •Ph.D.Student• Department of Civil Engineering
Vibrations from blastingVibrations from blasting
Measuring Rocks: Sensors is bolted to the rock Unconsolidated soil: The sensor is buried in a box
Kim André Larsen •Ph.D.Student• Department of Civil Engineering
Vibrations from blastingVibrations from blastingMeasuring Type of sensors
– Velocity gauge measures the particle velocity– Acceleration seismograph
Kim André Larsen •Ph.D.Student• Department of Civil Engineering