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Chapter 26 required when the job is started and seismic data are available. Fot ~, example, this formula does not apply to: 'I • Unusually large blasts (such as lazge coyote or nuclear explosions), ~, In such blasts the square root scaling does not apply and the three ~. constants in the first equation must be determined empirically by a;; series of seismic calibration test blasts. _ • Charges fired with a high degree of confinement, such as in the8 ' opening holes of the burn cut in a heading or in presplit blastingr Under these conditions the peak particle velocity may be five times~t ' or more greater because there is no nearby free face to provide relief. - • Blasting patterns which use many holes on a particular delay period. These patterns generally produce smaller vibration than those with ' a single hole on a delay period having the same total charge weight This effect occurs because of the scatter of the bring times of the ~ detonators and because of the spacial distribution of the charges. How to Measure Seismic Naves. Special instruments, known ee ~ seismographs, measure the particle motion associated with seismic ~ waves. The three main types are: • Displacement: These machines record the amplitude of [he seismic ~ wave at a particular location as a function of time - on paper, film,. or tape. • Velocity: These machines record particle velocity of the seismic wave at a particulaz location. Particle velocity is the rate of change in the wave's amplitude as a function of time. It is the most widely used seismograph machine for measuring ground motion generated I by blasting operations. -~A~CJ~11 Vertical - 0.13 ips Longitudinal - 0.10 Ips Transverse - 0.15 Ips I I I I I I I I 1 I f----~ 0.1 see. Figure Z6-C. A three-component recording of gmund motion 1,6001eet behind the lace of an eight-hole 4,BOo-pound quarry bleat In trap rock where 6V.-inch diameter holes on 65-toot lace were Mrod In sequenu at t5 me Intervals using delay electdc blariing capti Vibration and Air Blast - Peak Particle Veloclly Inches per second Nature of Damage ~--- 12 Fell of rocks In unlined funnels 7,5 SOWn Probeblllry of melor plaster damage 5.4 SOrb Probablllry of minor plaster damage 2.8-3.3 Threshold of damage Irom close-In blasting. 2.0 Ssle blasting criterion for residential structures recommended by U.S. Bureau of Minas. • Fgure Y6-D. Damage levels from ground viorenpn es a ~u~w„~„ ~~ r~~^ r^^•-•- -°---• pl ground motion near structures. Perceptible motion level b people is about 0.01 ips. • Acceleration: These machines record the rate of change of the parti- cle velocity at a particulaz location as a function of time. They are most frequently used to record strong ground motion produced by earthquakes. Nearly all seismographs record the pazticle motion of seismic waves in three mutually perpendicular directions. One horizontal compo- nent is usually oriented in the direction of the blast and records the radial or longitudinal motion. The other horizontal component records the transverse motion. The third component measures the vertical ground motion. Engineering seismographs are normally constructed to measure particle velocities ranging from about 0.1 to 10.0 inches- per-second over a frequency range of 2 to 200 Hz (cycles-per-second(. A three-component recording taken 1,600 feet behind the face of an eight-hole, 4,800-pound quarry blast is shown in Figure 26-C. .Effects of Seismic Waves on Structures. The intensity oC seismic motion that can be tolerated by various kinds of structures must be • established before acceptable chazge weights at various distances can be determined. Obviously, the level of motion required to damage a structure depends upon its construction. For example, setae(-framed warehouse can tolerate a more intense seismic wave than a residen- tial structure with plaster walls. Because plaster is the weakest of the most commonly used materials of construction, and because of the prevalence of such structures, most damage criteria are based on this type oC structure. A number of studies have been made to correlate vibration levels with observed damage. These studies, included in Figure 26-D, show that the amount of damage is related to the pazticle velocity of the ground motion peak. 429 429