Underground Stemming provides unique overhead blast hole stemming solutions. Several years of prototyping and design for manufacture has resulted in the injection moulded Pineapple stemming plug. The plug is made out of glass-reinforced nylon for strength. The design is initially available in 102mm with other sizes to follow.
Pineapple stemming plug
Blasting underground orebodies gives rise to a trade-off between good fragmentation and preventing damage to surrounding areas. Good fragmentation makes ore easier to dig underground and lowers crushing costs. A high powder will provide good fragmentation but will be detrimental to the overall integrity of the surrounding infrastructure (ore drive, pillars, cross cuts etc). The balance of good fragmentation and limiting damage surrounding a stope can be difficult to achieve.
The alternative, of course, used in open pits worldwide, is to stem the blast holes. However, since the blast holes are overhead, stemming against gravity is not straight forward. In the past, there has been a lack of stemming choices for overhead production blast holes underground. The Pineapple stemming plug changes this.
Stemming of overhead blast holes allows the Drill and Blast Engineer to refine the blast design to improve fragmentation, reduce damage, and reduce the overall cost of blasting.
The Pineapple stemming plug is pushed up with the charge hose in the blast hole to within a metre of the explosives. It can be pushed up any distance, locks out on retraction of the charge hose, and is removable in case of a misfire.
On initiation, the plug works by the upper wedge pistoning down against the lower wedge. Serrations on each wedge assist with the relative movement.
The Pineapple stemming plug can also work as decking, preventing sympathetic detonation across the deck.
Slashing shots using dumped holes to knock out bridges can easily damage ground support and other infrastructure in the area. The Pineapple stemming plug is designed to prevent blast damage and costly rehabilitation, ie re-bolting and meshing, from slashing shots.
The Pineapple stemming plug has been designed as an alternative to grouting collars for the construction of modern block cave undercuts, and firing an orebody from the footwall drive to protect access.