A dissertation submitted to the Faculty of Engineering, University of the
Witwatersrand, Johannesburg, in fulfilment of the requir tents for the degree of
Master of Science in Engineering. Johannesburg 1996.The design of bord and pillar working in South
African collieries is based on the pillar strength
formula developed by Salamon and Munro1967 and
which has been used widely since then for designing
pillars. This formula is based on the statistical
analysis of 27 collapsed and 98 intact coal pillar
cases from collieries located in the Transvaal and
the Free state.
The main objective of this study is to establish the
difference in the strength of the coal material in
ditferent seams by means of laboratory testing. In
this manner, some 753 coal samples from 10
collieries from 4 seams were tested.
The size and width to height ratio effects on
strength were analysed. The size effect showed that
the difference between the seams was obvious, with a
difference of 59,4 per cent between the strongest
and weakest coal.
The statistical re-analysis showed that the strength
of the six blocks from the No 2 seam, Witbank
Coalfield occurred in a fairly tight strength range;
and that laboratory coal strengths from individual
seams or mines could deviate to a significant
although relatively small extent from the overall
average.AC201
