α: Attenuation coefficient (range 0.5 - 2) 2.2.1 Ground vibration attenuation law From the blast vibration monitoring carried out at the María Teresa mine, a set of 75 seismographic records obtained was grouped (Figure 4), from which the following scatter plot was obtained: Figure 4. PPV values registered by the seismographs at María Teresa. Source: Orica Blast Engineering From the graph above, by plotting the trend line of the data distribution with respect to the scaled distance, a general ground attenuation law is obtained: PPV = 1909.83 x( DඥQ )−2.01 This attenuation law has a correlation coefficient (R²) of 0.87, which is acceptable. However, for each peak particle velocity (PPV) value estimated with this model, the probability of not exceeding the established limit will be 50%. This scatter results in moderate correlation in direct fits (R² typically 0.70-0.90) and can cause the fitted attenuation exponent α to deviate from the value that best captures the observed far-field decay. 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).
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