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Blasting Impacts Assessment for the Proposed GCC Rio Grande, Inc. Quarry in Pueblo County, Colorado <br />Displacement is a measure of ground particle travel distance or location with respect to time. <br />Particle velocity measures the speed of movement and acceleration is the rate of velocity changes. <br />Vibration frequency is a measure of how many oscillations a ground particle makes per second of <br />time. Frequency is reported in units of Hertz (Hz), which is equivalent to cycles per second. <br />3.2 Vibration Perception and Damage Criteria <br />The average person is quite sensitive to ground motion, and levels as low as 0.50 mm/s (0.02 in/s) <br />can be detected by the human body when background noise and vibration levels are low. A curve <br />plotting intensities of ground motion and motion frequencies that will not cause cosmetic cracking <br />in drywall and plaster -lath walls are shown in Figure 3.3. Vibration intensity is expressed as Peak <br />Particle Velocity (PPV), which is simply the maximum speed that the ground moves while it <br />temporarily shakes. Since ground- shaking speeds are very small, it is measured in inches per <br />second (in/s). Frequency units are hertz (Hz) or cycles per second, which is a measure of how <br />many times a particle of ground shook back and forth is one second. These limits "safe limits" <br />published by the US Bureau of Mines (USBM) in Report of Investigations (RI) 8507, are intended <br />only to protect typical wood frame homes. Significantly higher PPV limits, ranging from 5.0 to 20 <br />in/s, are used to protect buried pipes and other heavy civil structures. <br />PPV <br />254 (10) <br />203 (8) <br />152 (6) <br />102 (4) <br />50.8 (2) <br />25.4 (1) <br />20.3 (.8) <br />15 2 (.6) <br />10.2 (.4) <br />5.1 ( 2) <br />2.5 (1) <br />USBM RI 8507 "Safe Level" Curve <br />2 <br />19.0 mm/s <br />(0.75 in /s) <br />Dirval <br />Mosier 8.1.21h <br />127 rant <br />(0.50 i1/s) <br />12 <br />4 6 8 10 20 30 40 60 80 100 <br />FREQUENCY, Hz <br />50.8 rrffnfs <br />(2.0 in/s) <br />40 <br />Figure 3.3 -- USBM "Safe Level" vibration curve from RI 8507 <br />REVEY Associates, Inc. Page 6 July 2002 <br />