Civil Engineering Reference
In-Depth Information
Table 11.5
Instantel DS677 technical specifications
All channels are autoranging. Seismic (three channels): (0-250 mm/s)
a
Air pressure (one channel): (up to 140 dB peak (200 kPa)
Ranges
Trigger
Seismic: 0.50-50.85 mm/s
levels
Air pressure: 92-129 dB (0.8-56.4 kPa)
Resolution
Seismic: 0.1245 mm/s
Air pressure: 1 dB (0.02 Pa)
Frequency
All channels 2-250 Hz,
±
3dB
response
(independent of record time)
Recording
Standard: 1-7 s in steps of 1 s
times
Option: 1-10 s in steps of 1 s
Additional 0.25 s pre-trigger in all records
Acceleration
Computed up to 30
g
with a resolution of 0.013
g
(0.01 displayed)
Displacement
Computed to 38 mm
Metric resolution 0.000127 mm, 0.001 displayed
Note
a Measurement units (Imperial or Metric) are user selectable in the field. Air pressure values are rms weighted.
Table 11.6
Peak particle velocity threshold damage
levels
Figure 11.20 shows the relationship between
peak particle velocity, vibration frequency and
approximate damage thresholds for residential
structures. This diagram demonstrates that with
increasing frequency,
Velocity (mm/s)
Effect/damage
3-5
Vibrations perceptible to humans.
the allowable PPV also
10
Approximate limit for poorly
constructed and historic
buildings.
increases.
Effect of geology on ground vibrations.
It has
been found that blast vibrations are modified
by the presence of overburden at the measure-
ment location. In general, vibrations measured on
overburden have a lower frequency and higher
amplitude than those measured on rock at the
same distance from the blast. A consequence of
this is that if the particle velocity is approximately
the same at two locations, the lower frequency
of the vibrations in overburden will make the
blast vibrations more readily felt by humans.
Vibrations in uncured concrete.
On some
construction projects there may be a need to carry
out blasting operations close to uncured concrete.
Under these circumstances, explosive charge
weights per delay should be designed to keep
ground vibrations within limits that are determ-
ined by the age of the concrete, the distance of
the concrete from the blast and the type of struc-
ture (Oriard and Coulson, 1980; Oriard, 2002).
Table 11.7 shows an approximate relationship
33-50
Vibrations objectionable to
humans.
50
Limit below which risk of
damage to structures is very
slight (less than 5%).
125
Minor damage, cracking of
plaster, serious complaints.
230
Cracks in concrete blocks.
factors as the type of blast, the distance between
the blast and the structure, and the material
through which the ground vibrations travel. Typ-
ical construction blasts produce vibrations with
principal frequencies in the range of about 50-
200 Hz. It is found that large quarry andmine
blasts produce vibrations with lower principal
frequencies than construction blasts, and that
principal frequencies decrease with increasing dis-
tance from the blast due to frequency attenuation.
