1863 2.2.2 Seismograph Calibration and Site-Specific PPV Damage Criteria To ensure that the blast design does not exceed the limit established by the standard (USBM RI 8507, 1980), the reliability level of the attenuation law must be increased. A practical and safe way to do this is to shift the curve obtained at 50% reliability upwards, parallel to the line, so that the points located below the line relative to the total number of points are numerically equal to the desired reliability value. Thus, with the 75 seismographic records, statistical analysis was performed to calculate the mean, standard deviation, and standard error. These parameters provided the input to estimate the confidence intervals and find the “K” coefficient at 95% reliability (See Table 6). Table 2 – Coefficient “K” determined at 95% reliability from the ground attenuation law at 50% confidence. Source: Orica Blast Engineering. Site Law Coefficients Site Coefficient 50 % Confidence 95 % Confidence K 1909.83 4820.30 -α -2.01 -2.01 Standard Error 0.21 Therefore, the 50% and 95% reliability curves were obtained, as shown here: Figure 5. Scatter plot with attenuation laws at 50% and 95% confidence. Source: Orica Blast Engineering. Based on the above, the ground attenuation law is used with a 95% reliability level because, under this constraint, the value of the maximum instantaneous charge (MIC) can be determined, thus avoiding the use of excess charge for the required blasting energy. Therefore, we have the following attenuation law: VPP = 4820.30 x( ã D Q )@#.<!
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