| Summary: | To make the method of coalmining known as 'strip-mining'
economically viable extremely large amounts of explosive need co
be detonated in any one particular blast. This is to ensure enough
rock is broken co keep the large earthmoving machinery, used in this
type of mining, productive. This type of coal-mining operation
was undertaken at Rieespruit Opencast Colliery in the Eastern Transvaal.
Adjacent to this colliery is an exiting underground coalmine,
and it was feared that the large amount of energy released
by the surface blasting would be sufficient to damage the coal pillars.
The investigation of the above problem formed the basis of this dissertation.
Moving-coil seismometers were installed underground in what was
considered^ a representative pillar, and continuous records of ground
particle motion due to blasting were obtained from these instruments.
Further field instrumentation consist of tape-recording decks and
electronic packages to amplify and record the seismic signals was located
on surface in an instrument hut built specifically for this
purpose.
The object of obtaining the above records was to establish damage
criteria, whereby change weight could be estimated, for given distances
from the blast to the underground workings, which would not cause appreciable
damage underground. Propagation laws were established relating
peak particle velocity, which is widely used as an indicator of
possible damage, to the distance from the blast and either the square root
or cube-root of the maximum charge weight per delay. These results
are presented graphically and could be used to determine allowable
charge weights to ensure a certain particle velocity is not exceeded.
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