1. Vibrations from blasting
Where is blasting used?
Mining
Construction
Demolition
New constructions
Densification
Kim André Larsen •Ph.D.Student• Department of Civil Engineering

2. Vibrations from blasting
Disturbance from blasting
Vibrations
Air blast (Low frequency air vibration)
Fly rocks
Kim André Larsen •Ph.D.Student• Department of Civil Engineering

3. Vibrations 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

4. Vibrations 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

5. Vibrations 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

6. Vibrations 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 Hz
Kim André Larsen •Ph.D.Student• Department of Civil Engineering

7. Vibrations 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

8. Vibrations 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

9. Vibrations 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

10. Vibrations 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

11. Vibrations from blasting
Measuring
Type of sensors
Velocity gauge measures the particle velocity
Acceleration seismograph
Kim André Larsen •Ph.D.Student• Department of Civil Engineering