3. Effect of Hole Stemming Practices on Energy Efficiency of Comminution

In order to increase the efficiency of explosive comminution, the borehole pressure must be maximized and pressure losses minimized. The majority of these pressure losses occur from premature borehole venting and through weak layers intersecting the borehole. With the use of proper stemming material and amount of stemming these pressure losses can be minimized, increasing the efficiency of explosive comminution. This chapter discusses the key considerations in the choice of stemming materials and methods calculate proper stemming size for different borehole sizes. In addition, the pressure models and methods to calculate stemming depth are discussed for both ideal and nonideal stemming material. Following the stemming design section, the chapter presents methods to improve stemming efficiency and reduce total stemming height including airdecks and stemming plugs. The chapter then addresses the issue of minimal fragmentation in the stemming zone. Practical design guidelines are presented for the use of a stem charge, allowing for breakage in the stemming zone.