Page 265 - Civil Engineering Formulas

SOIL AND EARTHWORK FORMULAS 199

Vibrations caused by blasting are propagated with a velocity V, ft/s (m/s);
frequency f, Hz; and wavelength L, ft (m), related by

V
L (8.55)
f
Velocity v, in/s (mm/s), of the particles disturbed by the vibrations depends on
the amplitude of the vibrations A, in (mm):

v 2
fA (8.56)
If the velocity v at a distance D from the explosion is known, the velocity v at
1
1
2
a distance D from the explosion may be estimated from
2
v 2 v 1 1.5 (8.57)
D 1
D 2
2
2
The acceleration a, in/s (mm/s ), of the particles is given by
2 2
a 4
f A (8.58)
2
For a charge exploded on the ground surface, the overpressure P, lb/in (kPa),
may be computed from
W 1/3 1.407
P 226.62 (8.59)
D
where W maximum weight of explosives, lb (kg) per delay; and D distance,
ft (m), from explosion to exposure.
The sound pressure level, decibels, may be computed from
P 28 0.084
dB 6.95 10 (8.60)

For vibration control, blasting should be controlled with the scaled-distance
formula:
D
v H (8.61)
W
where constant (varies for each site) and H constant (varies for each site).
Distance to exposure, ft (m), divided by the square root of maximum pounds
(kg) per delay is known as scaled distance.
Most courts have accepted the fact that a particle velocity not exceeding 2 in/s
(50.8 mm/s) does not damage any part of any structure. This implies that, for this
velocity, vibration damage is unlikely at scaled distances larger than 8.