Civil Engineering Reference
In-Depth Information
(a)
(b)
Sound
speed
Temperature
Rays
Wave
front
No trouble
No trouble
Potential trouble
Inversions—Potential trouble
Wave front
Potential trouble
Escapes
Figure 11.24
Effect of atmospheric
conditions on air blast: (a) variation
of temperature and sound speed
with altitude; (b) corresponding
pattern of sound rays and wave
front (Baker, 1973).
Rays
Totally refracted
Reflection
Curl up
Quiet
spot
Intense
region
Temperature or sound speed
The decrease of sound pressure with distance
can be predicted by means of cube root scaling.
The scaling factor with distance
K
R
is given by:
out by the US Bureau of Mines in a number of
quarries. The burden
B
, was varied and the length
of stemming was 2.6 ft per inch (0.31 m stem-
ming per cm) diameter of borehole. For example,
if a 1000 lb (454 kg) charge is detonated with a
burden of 10 ft (3.1 m), then the over-pressure
at a distance of 500 ft (152 m),
R
K
R
=
√
W
(11.18)
3
is found as
follows:
where
R
is the radial distance from the explosion
and
W
is the weight of charge detonated per delay.
Figure 11.26 gives the results in the original
English units of pressure measurements carried
R
500
√
W
=
√
1000
=
50
3
3
