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Janice Lynn Bennett - 81422.PDF <br />Blasting Impacts Assessment for the Proposed GCC Rio Grande, Inc. Quarry in Pueblo County, Colorado <br />3.5 Blast Vibration Intensity Predictions <br />It is standard practice to use scaling relationships to predict vibration intensities at various <br />distances. These relationships, based on similitude theory, are used to develop empirical <br />relationships between ground vibration particle velocity, charge weight, and distance. Distance is <br />scaled by dividing it by the square root of the maximum charge weight firing at any time within a <br />blast. This single scaled distance variable can than be used to predict vibration intensity (PPV). <br />The scaling relationship between peak - particle- velocity (PPV) and scaled distance (D) is shown <br />below in Equation 3.2. <br />Where: <br />1 REVEY Associates, Inc <br />Equation 3.2 <br />PPV = Peak Particle Velocity (in /s) <br />D = Distance (ft) <br />W = Maximum Charge- weight - per -delay (lb) <br />K = Rock Energy Transfer Constant (K- Factor) <br />m = Decay Constant <br />D = Scaled Distance (m -kg o 5) <br />Site - specific constants, K and m, can be determined by performing a regression analysis of <br />multiple peak particle velocity (PPV) and D data pairs. In simple terms, for any given site, K is a <br />measure of how much vibration energy is transferred to the ground near the explosive charge and <br />m defines how fast the energy attenuates with distance. As suggested by CO- DNR -DMG in their <br />comments regarding the GCC mining permit application, new blasting operations usually measure <br />vibration intensities with several seismographs at varying locations in order to collect data that can <br />be used to define site - specific curves that are later used to develop appropriate limits on charge <br />weights based on distances to structures or other points of concern. <br />A sample regression curve that was recently prepared by the author to support blasting controls for <br />an upcoming subway project in New York City is shown in Figure 3.4. When plotted in log -log <br />scale, the exponential relationship between scaled distance and PPV generally follows a straight <br />line with a negative slope (m) -- usually around —1.6, and Y- intercept (K) values varying between <br />960 and 26, as defined by Oriard (1972). The K value (amount of energy at the source) is higher <br />when charges are more confined and /or rock has a high stiffness ratio (Young's modulus of <br />elasticity). <br />Page 10 July 2002 <br />Page 13 <br />