Abstract
M.Sc. (Geology)
The purpose of this work was to attempt to understand the
behaviour of the ground around a series of holes bored in
gold bearing rock by a reef boring machine. Furthermore
this ground behaviour is compared with existing theoretical
concepts of rock behaviour.
The experimental boring site and the sequence of events
at that site are described. The state of the rock
surrounding the excavations is observed to deteriorate
with increase in mining. The fracturing observed is
characterised by spalling on the sides of the bored holes.
This spalling increases in severity with closeness to the
bored out region.
Calculations of the stress acting on the sides of the
bored holes were made from elastic theory using two
techniques. One of these was a quick graphical technique
and the other was a more complex analytical one. The
analytical technique was used as a check on the results
of the graphical technique.
Finally the extent of spalling on the sides of the holes
is compared with the theoretical stresses. A close
correlation is found, and spalling appears to start when
the stress level reaches the strength of the rock. As the
stress level increases spalling increases in severity
until such time as the ground around the bored area is
fractured by large through going fractures. At this stage
holes bored in this ground no longer spall.