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www.rockproducts.com ROCK products • August 2016 • 49 overpressure. In addition, precision presplitting generally has higher air overpressure levels than a regular production blast at the same scaled distance. Air overpressure has a different scaled distance than normal ground vibration, where air overpressure scaled distance is: SD AP = D ∛W Where: SD AP = Air Overpressure Scaled Distance D = Distance from the blast (ft.) W = Maximum Charge per 8 ms delay (lb.) For this equation, the charge per delay is measured in pounds. To accurately estimate this the detonating cord used in pre- cision presplitting must be converted to pounds. This can be done by dividing the grains of detonating cord by 7000 which is shown in the equation below: E lb = E gr 7000 Where: E lb = Explosive Load in lb. E gr = Explosive Load in Grains Now that an accurate air overpressure scaled distance can be calculated one can use the chart below (Figure 2) to estimate the maximum air overpressure from a precision presplit. The graph below is shown on logarithmic scale with the vertical (y) axis having a maximum value of 200 and a minimum of 100. Figure 2 - Konya Precision Presplit Air Overpressure Prediction The next environmental concern is the ground vibration from a precision presplit. From a normal presplit, the common assumption is that it can be five times greater than a normal production blast. The authors conducted a study to predict the ground vibration from precision presplitting and produc- tion blasting to create a comparison. What was found was that the ground vibration from a precision presplit at lower scaled distances was less than a production blast, and at the higher scaled distances was slightly more. Ground vibration follows the typical square root scaled dis- tance which is shown below: SD PPV = D ∛W Where: SD PPV = Scaled Distance for Ground Vibration. D = Distance from a blast (ft.) W = Maximum Charge per 8ms Delay (lb.) Again the conversion to pounds instead of grains must be used. After a scaled distance is found, one can use the chart below to calculate the ground vibration from a precision presplit (Figure 3). Figure 3 - Konya Precision Presplit Ground Vibration Prediction An example of how one can apply these methods to design a Precision Presplit. The scenario for the design is: • Limestone Surface Quarry with 30-ft. benches. • Residential Structures at 1,000 ft. – 132 Db Maximum Air Overpressure. – 2 in./s maximum ground vibration. • 4-in. drill hole. • Closest drill spacing is 30 in. • No subdrill on presplits. To begin, the explosive load for limestone at a 30-in. spac- ing must be calculated. Using the graph in Figure 1 this is an explosive load of about 850 grains per ft. of detonating cord. With a 4-in. borehole approximately 40 in. (3.33 ft.) of stemming will be used. Then the total powder column must be calculated, this is the total drillhole length minus the stemming height (30 ft. 2