Testing stemming performance, possible or not?
D Boshoff, RCW Webber-Youngman
The ability of an explosive to break rock is influenced considerably
by the extent of confinement in the blasthole. It is believed that
confinement is improved by the use of adequate stemming. The aim
of this paper is to present the results of the first and second stages
of developing a stemming performance testing rig for small diameter
boreholes. The rig was used to compare and contrast the
performance of different designs of products. The results showed
that different stemming products have differences in terms of their
functionality, which can have a major impact on the efficiency of
rock breaking. Two test procedures were used, one through the
exclusive use of compressed air and the second using a purposebuilt
high pressure test rig with small quantities of explosives.
Both tests were used to identify and evaluate the ability of
various stemming products to resist the escape of explosive gas
through the collar of a blasthole. An investigation was done to
determine the types of stemming products most commonly used in
South African underground hard rock mines, and these products
were used during the tests. The first stage of tests using compressed
air only did not prove adequate to predict with certainty the
pressure behaviour in the borehole of a particular product under
high pressure conditions.
The purpose-built high pressure test rig also did not prove to be
a very effective tool to test stemming products under high pressure
conditions. The test rig incorporated only the effect of gas pressure
on the stemming product, and excluded the effect of the shock
wave. This study therefore proved that to take into account only
the gas pressure generated in the blasthole is not sufficient to
effectively test stemming product performance.
Keywords: explosive, break rock, confinement, blasthole, stemming
performance testing.