Student Number : 0400188H -
MSc(Eng) Dissertation -
School of Mining -
Faculty of Engineering and the Built Environment / The occurrence of fracturing due to high stress levels is a major factor with regard
to hangingwall stability in deep level gold mine stopes. However, rock falls
cannot be the result of these fractures alone. Blocks in the hangingwall strata must
be defined by a combination of the stress induced fractures and naturally
occurring geological planes of weakness. These planes include bedding planes
and joint planes. The importance of the natural joints and bedding planes in
defining the instability has not been given the attention that it deserves, to the
extent that there are apparently no documented, published data available on joint
set characteristics. This is perhaps an indication that such data do not exist on the
mines. To remedy this situation, detailed scan-line joint mapping exercises have
been carried out in several geological environments in two gold mines. The joint
data collected on joint geometry included orientation, spacing and length. The
results presented in this dissertation are believed to be the first such data available
on jointing in gold mines. The main conclusions from the interpretation of these
data are that there are two dominant joint sets in stope hangingwalls and at least
one of these sets is shallow dipping. In development tunnels there is one
predominant set of shallow dipping bedding planes. Both in stope hangingwalls
and in development tunnels, steeply dipping random joints constitute half of the
mapped joints.
The statistical joint data obtained was used to investigate and analyse the potential
for rock falls in stopes. This involved the prediction of characteristic block
parameters such as expected block sizes and rock fall thicknesses. These
predictions show good agreement with measurements made of actual rockfalls
(generic results). Most unstable blocks in stope hangingwalls are less than a cubic
meter in size. These blocks are more likely to fall between support elements than
fail the supports, whilst failure of the fewer large blocks (20%) usually involves
failure of support elements. It is concluded that failure probabilities are largely
related to joint geometry. Common failure modes for small blocks are single plane sliding and ‘dropping out’ whilst larger blocks usually fail by rotation. The study
increases understanding of rock fall mechanisms and the support-block
interaction. The results of the analyses of block stability that have been reported in
this dissertation show disturbingly high probabilities of failure in the stope face
area (or working area), particularly for blocks that are smaller than about 1.5 cubic
metres in size.
The study has demonstrated the important influence that natural joints have on
hangingwall block stability, and the importance of joint mapping to produce
statistical joint data that can be used in the assessment of stability against rock
falls. Although joint mapping may be a tedious exercise in mines, it has been
shown to give similar results regarding heights of rock falls to that interpreted
from collection of empirical incident and accident record data over a ten-year
period. It is considered that this could provide good input data for the design of
stope support.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/2129 |
| Date | 26 February 2007 |
| Creators | Gumede, Hlangabeza |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 3122610 bytes, 24923 bytes, application/pdf, application/pdf, application/pdf, application/pdf |
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