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~r <br />5{ <br />E <br />~'. <br />Chapter 26 <br />mined based nn the kind of rock sm~rounding the explosive and at the <br />receiving site ++~here the particle motion is measw'ed. (Experience <br />has sho+m that ddferences in vibration levels caused by different <br />kind; of commercial expl o;ives are usually small compared to the <br />variatimts caused by other factors.( <br />•m and n are empirical constant; based primarily on the overall <br />geolohry between the explosion and receiving sites. <br />• R is the distance between the explosum and receiving sites. <br />Rork by the U.S. Bureau of Mines in grround motion transmission <br />produced hvo particularly significant results for the typical charge <br />weights and distances found in surface blasting: <br />• The constant m is equal to one-half of the constant n. <br />The power law equation then has only hvo unknowns and assumes <br />the following form: <br />where the quantit}' R/1Y" is kno+cn as the scaled distarrce. <br />•The peak particle velocity depends on the maximum charge- <br />weight-per-delay and not on the mtaf charge weight, prodding the <br />delay interval is eight millisecmrds or more. <br />These results. combined with a large number of field measure- <br />ments, have shown that the propagation equation can topically be <br />expressed as follows: <br />fi -~.~: <br />\' = 160 - <br />R "1 <br />where <br />\' =peak particle celocih~ in ips <br />~ cinches persecondl <br />[ R =distance between explosion and <br />recording sites in feet <br />~ tV =maximum pounds-per-delay-period <br />of eight milliseconds or more <br />Blasters can use this equation to estimate the peak particle veloci [o <br />of a seismic ++ace or they can use [he graph shown in Figirre 26-B. Far <br />example. Determine the typical peak particle velocity from a nor- <br />mally cm+fined blast with a maximum charge-weigh[-per-delay-period <br />of 400 pounds at a distance of 1.000 feet from the receiving site. 'Che <br />•~~ scaled distance. R'R"' = 1.000/-toll" = 50 cm'responds to a peak <br />~ particle velocity of 0.31 ips on the graph. <br />-, It should be emphasized that the expression Siren in the above <br />+ •• equation relating the peak particle velocity, charge-weight-perv <br />M.~~ dela}•-period, and distance provides h'picaf values only for planning <br />' blasting projects in the absence of seismic data. Modification may be <br />i 426 <br />tlL <br />i <br />Vibration and Air Blast <br /> <br />6 <br />5 <br /> <br />4 <br /> <br />3 <br />c <br /> <br />~ 2 <br />m <br />d <br />a <br />w <br />r <br />0 <br />c 1 <br />. <br />0.9 <br /> <br />0.8 <br /> <br />0.7 <br />v <br /> <br />0 0.6 <br />tg <br />~ <br />0.5 <br />d <br />_ <br />~ <br />0.4 <br />t <br />to <br />a <br />x 0.3 <br />ra <br />W <br />a <br />0 <br />2 <br />. <br />0.1 <br /> <br />10 15 20 25 30 40 50 60 70 80 90100 <br />Scaled Distance - ft./Ib.t~2 <br />Fgure 26-B. Typical values of peak particle velocity as afunction o/ scaletl distance for <br />blasting to a Ireelace. Chargb weight caper-tleley-period of eight mllllsecontls or more. <br />Blasts made under tight continemenl such as the opening of holes In heatlinga or In <br />presplitting may give values Live Ilmes more than typical under normal conlinement. <br />427 <br />x ~ <br />L ~` <br /> <br />~ ~ <br />i <br /> ~-I <br />~ '~i <br />~ <br />~~ <br /> \ G ` <br />~ <br />L <br /> ~~qe <br />c <br />~~ <br /> ^, <br />x <br />GF <br />1 <br />x J <br />4 <br />~~ <br /> P <br />/ \ ~ <br /> P <br /> vx ~ x <br />it <br />v 1 <br />~~ <br />~ <br /> x <br />~ v <br />~ ~ <br />x <br />7 <br /> <br /> ~~ ~ 7 x ~r <br /> ~ <br /> ~ ~ <br />~ <br /> ! <br /> •' '~ <br /> ~ ~ <br /> ~ <br /> ~ v <br /> i <br /> x <br />x <br /> v <br /> l + <br />• <br />• <br />