Blasting in Norwegian mines is often carried out by contractors who tend
to look for the cheapest solution, without concern about fragment quality.
The requirementsfor a contractor are usually only related to the maximum
size of boulders and the quantity per month. Even when the owners of the
mine are responsible for blasting, very little effort is made to optimise the
blasting process. This paper presents test methods which were used and results from
small-scale and full-scale blasting tests. In the small-scale tests, cubes
500 x 500 x 500 mm of four different rock types were blasted in a
chamber, using two types of dynamite explosive. The velocity of
detonation (VOD) for the dynamite explosives was 3000 m/s and 6000
m/s respectively. Three cubes of each rock type were blasted with each
type of explosive, and a total of six cubes of each rock type was used.
The entire muckpile (approximately 350 kg) was- sieved and weighed
after each blast and fragments between 8-16 mm were tested for impact
values and flakiness. The results of these tests clearly showed improvement in fragmentation
the closer the acoustic impedance ratio of the explosive (VOD x density)
over the rock (Cp density) was equal to one. The results also showed that
the quality of the fragments (in terms of impact values) tends to be better
when the cubes are blasted with the high velocity dynamite.