In this video Anthony Konya of KonyaInc.com explains stemming and stemming calculations. Stemming is a material that is put inside of a blast hole to help prevent gases from escaping.
While stemming is typically put in the top of a blast hole, it can also be used to help bridge mud seams or weak layers. Improperly placed stemming can greater decrease fragmentation size. This is because if a stronger layer is stemmed that means their is no explosive to fragment that strong rock. In weak layers the rock is already being easily broken up. When stemming across a seam it is also important to put primers in both powder columns and ensure that both will fire. This can be difficult and here at Academy Blasting we spend a good amount of time taking student through many variations of connecting powder columns for proper initiations.
Stemming is also extremely important in the top of a blast hole. Using proper stemming is one of the best ways to increase your fragmentation and sizing ranges. Stemming relies on many of the same variables as burden, and because of this we can use a simple equation to calculate the appropriate stemming depth.
Stemming (feet) = 0.7 x Burden (feet)
Stemming (meters) = 0.7 x Burden (meters)
It is important to note that these equations are made for using appropriate sized stemming. A good stemming is crushed rock as it will form a plug in the hole, confining the gases. Drill cutting are commonly used because they are easy to get and are much cheaper to use, however they will not form a good plug in the hole. Most drill cutting will blow out and lose confinement of the gases. If drill cuttings are used then these equation might be as much as Stemming = 1.1 x Burden. Next we will show you how to calculate the optimal stemming size.
Stemming Material Calculations
Material Size (inches) = diameter of hole (inches) / 20
Material Size (mm) = diameter of hole (mm) / 20
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