Abstract:
This paper describes some important aspects associated with historical underground measurements in
South African gold and coal mines. Deformation measurements were used to confirm the use of elastic
theory to simulate the rock mass behaviour in the Witwatersrand gold mines in the 1960s. Although
a prominent time-dependent component of stope closure was measured as early as the 1930s, it was
ignored owing to the benefit of adopting elastic theory. Neglecting the time-dependent response of
the rock for many decades resulted in important aspects such as the effect of mining rate, the effect
of advance per blast, and the need for enhanced design criteria not being explored. Recent work is
only now starting to address this gap in knowledge. In-situ measurements of large coal specimens in
the 1960s and 1970s indicated that a linear formula may possibly be a better approximation of coal
pillar strengths. This alternative formulation was never adopted, however, as the power law strength
formula was already deeply entrenched in the industry at that stage. In spite of these apparent failures
to continuously generate and adopt new knowledge, a key lesson learnt is that major advances in rock
mechanics will not be possible without careful monitoring of the rock mass behaviour in experimental
sites. Areas requiring further research, such as pillar strength formulae for the Bushveld Complex
and enhanced design criteria for the gold mines, can only be developed using extensive underground
monitoring programmes.
