Scaled Distance for Blasting
Scaled Distance Calculations
Scaled Distance is discussed and methods for calculation are given in this video for both ground vibration and air overpressure from blasting.
Scaled Distance is a commonly used technique for estimating the vibration and air overpressure from blasts. The term scaled distance is given because the blast where the weight fired per 8ms delay is scaled to one pound of dynamite. For example, in this video Anthony Konya explains that if 25 pounds of explosive is detonated, the estimated power at 180 is similar to that of one pound of dynamite at a distance of 36 feet.
If two blasts that are different from one another, such as open air versus bench blasting, they may have the same scaled distance yet produce drastically different environmental results. However, different models exist for different situations, such as the USBM RI 8507 ground vibration prediction model for bench blasting. These all rely on these basic scaled distance calculations; a word of caution though, these models are predictive and are very different for each site. These models generally contain the form:
PPV = K*Ds^-B
Both of the variables, K and B, change significantly where K can vary from 10 to over 500 and B can vary from 0.8 to over 3. These have large implications and differences in prediction and each site must have there own equations compiled for prediction of peak particle velocity and air over pressure (Company who can complete this work can be found here).
Furthermore, scaled distance from blasting is also important from a regulatory standpoint. Certain states do not require the use of a seismograph dependent on the scale distance of the blast; however, the use of a seismograph is always recommended. Scaled Distance calculations are a critical part of most blast design and planning procedures, and are necessary for blast reports.