Vibrations from blasting Where is blasting used? Mining Construction – Demolition – New...

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


Vibrations Air blast (Low frequency air vibration) Fly rocks


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.



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



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



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



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)



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



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.



Measuring Rocks: Sensors is bolted to the rock Unconsolidated soil: The sensor is buried in a box


Vibrations from blastingVibrations from blastingMeasuring Type of sensors

– Velocity gauge measures the particle velocity– Acceleration seismograph


Vibrations from blasting Where is blasting used? Mining Construction – Demolition – New...

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