Subsidence caused by high extraction coal mining in the Sasolburg and Secunda areas : prediction thereof and the mitigation of its effects
Date
1991
Authors
Van der Merwe, Jacob Nielen
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Abstract
The thesis describes the results of research which was done over
the period 1985 to 1990 in the Sasolburg and Secunda areas into
the effects of underground high extraction coal mining on the
surface, surface structures and agriculture.
Legal restrictions on the undermining of structures potentially
sterilize more than 30% of the coal reserves in the study area.
The basic motivation for doing the research was that most of the
restrictions could be overcome if methods could be developed to
undermine structures safely and economically.
For subsidence data analysis, a computerised three dimensional
method of analysis, the Surface Element Analysis (SEA) approach,
was developed and implemented. Using the results of the
analyses and analytical considerations, a subsidence profile
prediction method was developed. The prediction method
incorporates a new approach to the prediction of strain, based
on the shape of the subsidence profile and the thickness of
deformable layers on surface.
The reactions of various commonly occurring structures in the
study area, namely bituminised roads, gravel roads, pipe lines
and conveyor belts, to subsidence were analysed. It was found
that although no consideration to subsidence was given in the
design of the structures, most could withstand the effects
thereof safely with only minor and relatively inexpensive
precautionary and repair measures.
With regard to agriculture, it is shown that while there are
mining induced effects, they are in general not severe. There
is, however, reason for concern regarding the long term and not
immediately apparent effects. Further work is thus very
necessary.
Overall, it was found that while a very cautious approach to
high extraction undermining had merits in the past, most of the
restrictions can be relaxed in the light of the knowledge which
is now available.
The important provision is that careful and detailed prior
investigations are necessary for each individual case, and that
a sound and responsible engineering approach must be followed.
Mines can derive substantial economical benefit from the
mitigation methods which are described.
A very important aspect is the administrative handling of the
undermining of structures. A coordinated multi disciplinary
approach, catering for communication and joint planning of
mining and infrastructure, is proposed. It contains the
essential elements of the Australian approach with modifications
for local South African conditions.
Description
A thesis submitted to the Faculty of Engineering, University of
the Witwatersrand, in fulfilment of the requirements for the
degree of Doctor of Philosophy
Keywords
Coal mines and mining -- Environmental aspects., Coal mines and mining -- Research., Ground control (Mining), Mine subsidences., Coal mines and mining -- Data processing.