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Paper Number: 159
Analysis
of pillar scaling in the Magdalena Colliery, Dundee, South Africa
Govender,
A.C.1, Hingston, E.D.C.1 and Mtshali,
S.2
1University
of KwaZulu-Natal, Discipline of Geological Sciences, School of Earth and
Environmental Sciences, Durban, Republic of South Africa
2Buffalo
Coal, Dundee, Republic of South Africa
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Pillar scaling within coal mines leads to devastating effects such as
roof falls that put the life of underground personnel at risk, as well
as have a significant impact on the production of coal. Scaling occurs
as spalling of coal from the rib-sides of the pillars within the seam as
a consequence of the mining methods used, such as the drill and blast
method, or due to zones of weakness within the coal, such as joint
planes.
A study of the occurrence of pillar scaling within the Magadalena
Colliery in Dundee, South Africa, has been undertaken in order to
investigate the impact of pillar scaling on the originally designed
factor of safety. Since 2008, a continuous miner has been used to
extract bituminous coal from the Alfred and Gus seams of the Vryheid
Formation by making use of the bord and pillar method. Prior to 2008,
the drill and blast method was used as the method of extraction of the
coal. Scaling of the carefully designed coal pillars alters the
dimensions of the primary support structures thereby reducing the
originally designed factor of safety. Analysis of the change in
dimensions of coal pillars present within the Magdalena Colliery was
done, in which measurements were made from the approximate position of
the original rib-side to the new and current rib-side that has been
created through scaling. The new safety factors were calculated using
the standard Salamon and Munro [1] formulae, using the data related to
the change in pillar dimensions. The original safety factors were then
determined using unaltered pillar dimensions that are represented in
panel maps. By comparing the original safety factors that were
implemented during the time of coal extraction to those calculated for a
specific period, a relationship between time and change in safety factor
was established. Since analysis was carried out on pillars with two
different dimensions (i.e. width to height ratio), an understanding of
the scale effect was further established.
The results obtained from this study indicate that scaling is not in
fact an exclusively time dependent variable, but instead relates
directly to the properties of the rock mass itself. Thus, a coal seam
that is highly fractured or subjected to cleating will suffer a greater
deal of scaling than a seam that is relatively intact. The pillars
consistent exposure to moisture over time accelerates the rate of
scaling, more so if the pillar is highly jointed and highly cleated.
Furthermore, the dimensions of the pillars created greatly influence the
rate and degree of scaling. This was evident in the two different pillar
sizes present in the mine and relates directly to the scale effect, in
which pillars with smaller sizes resemble an intact rock specimen, while
those with larger dimensions resemble a discontinuous rock mass.
Reference:
[1] Salamon and Munro (1967) J. S. Afr. Inst. Min. Metall., 68(2):
55-67
