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ChaAter26
mined based on the kind of mck surrounding the explosive and at
receiving site where the particle motion is measured. (Experi¢
has shown that differences in vibration levels caused by differ
kinds of commercial explosives are usually small compazed to
variations caused by other factors.)
• m and n are empirical constants based primarily on the ova
geology between the explosion and receiving sites.
• R is the distance between the explosion and receiving sites.
Work by the U.S. Bureau of Mines in ground motion transmis~~
produced two particularly significant results for the typical chi
weights and distances found in surface blasting:
• The constant m is equal to one-half of the constant n.
The power law equation then has only two unknowns and asst
the following form:
where the quantity A/W"= is known as the scaled distance.
• The peak particle velocity depends on the maximum charge-
weight-per-delay and not on the total charge weight, providing the
delay interval is eight milliseconds or more.
These results, combined with a large number of field measure.
menu, have shown that the propagation equation can typically be
expressed as follows:
R l-~ s
V = 160 W" /
where
Scaled Distance - ft./Ib.'r2
V =peak particle velocity in ips
(inches per second)
R =distance between explosion and
recording sites in feet
W =maximum pounds-per-delay-period
of eight milliseconds or more
Blasters can use this equation to estimate the peak particle velocity
oC a seismic wave or they can use the graph shown in Figure 26-B. For
example: Determine the typical peak particle velocity from a nor
molly confined blast with a maximum charge-weight-per-delay-period
of 400 pounds at a distance of 1,000 feet from the receiving site. The
scaled distance, R/W"'. = 1,000/400"': = 50 corresponds [o a peak
particle velocity of 0.31 ips on the graph.
It should be emphasized that the expression given in the above
equation relating the peak pazticle velocity, charge-weigh Lper-
delay-period, and distance provides typical values only Tor planning
blasting projects in the absence of seismic data. Modification may be
426
Vibration and Air Blast
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Flgure 26-B. Typical values of peak panicle velocity es a function of scaled distance for
6leeting to s Iree lace. Charge weight Is per-delay-period of eight milliseconds or more.
Blasts made under tight confinement such es the opening of holes In headings or In
presplltting may give values Ilve times more then typical under normal conllnament.
427
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