User's Manual

96
RIOTRONIC X+
User Manual
Explosives distribution is very dependent on the rock mass to be blasted. If a single bed of
strong massive rock lies within relatively weak/soft materials, a high energy fully coupled
charge should be placed in that part of the blast-hole within the strong rock. In weaker
material, a lower energy charge should be located both below and above the strong bed.
If poor fragmentation is causing problems in the collar area, a small pocket charge can be
located centrally within the stemming column. The size of this pocket charge should be
sufficiently small to prevent excessive air blast, fly rock and overbreak, but large enough to
help break any massive blocks which lie alongside the stemming. A cheaper and easier
alternative is to increase the uncharged length and reduce stemming by the introduction of
an air deck.
Main points –explosive distribution
 Explosive column length should be at least 20-hole diameters for effective
distribution.
 Change the distribution of the explosives for soft rock, cavities, insufficient burden
or excessive toe burden.
 Explosives distribution should be called energy distribution.
 Pocket charges may be used in the stemming to break up strong collar rock.
9.3.7. Stemming
The function of stemming is to contain the explosion gases to assist in fracturing rock, heave
and to reduce blast nuisances such as air blast and fly rock. For a given blast, this means
burden and/or spacing can be increased significantly if a suitable type and quantity of
stemming is being used.
Good stemming provides both inertia (weight of the stemming) and, more importantly,
frictional resistance (locking of angular rocks/grains) to contain the high-pressure gases
following a detonation. For this reason, water, mud and fine drill cuttings are ineffective
forms of stemming as they only rely on inertia to contain the gases.
The general rule for the size of stemming to be used is 10% of the blast-hole diameter.
i.e. for a 208mm blast-hole, the stemming material should be approximately 20 mm in size.
The maximum stemming size, regardless of the size of the blast hole, is about 25 mm, as
anything larger than this tends to damage the initiation down lines.
Stemming length increases if the blast-hole diameter increases.