The two components of pillar design formula being used in South Africa are pillar strength and pillar load. While considerable effort has been directed to the determination of pillar strength, the other half of the safety factor equation, the load, has not received the same amount of attention. The load acting on pillars has always been calculated using the Tributary Area Theory (TAT). This paper summarises the recent studies on coal pillar loading using various numerical models. It concludes that although there are meaningful differences under certain circumstances, there is still a compelling argument to use the TAT in coal pillar design.

Les deux parties composantes de la formule de conception de pilier generalement utilisee en Afrique du Sud sont la resistance de pilier et la charge de pilier. Tandis que des efforts considerables on ete diriges vers la determination de la resistance de pilier, l'autre moitie du facteur de securite n'a pas reçu la même attention. La charge agissant sur les piliers a toujours ete calculee avec la Theorie d'Aire Tributaire (TAT). L'etude presente resume les etudes recentes sur la charge de pilier de charbon utilisant des modèles numeriques varies. La conclusion est que bien qu'il y ait des differences significatives selon les circonstances, il y a toujours un argument puissant pour utiliser le TAT dans la conception de pilier de charbon.

Die in Suedafrika fuer die Auslegung von Pfeilern verwendeten zwei Formelkomponenten sind Pfeilerstarke und Pfeilerbelastung. Wahrend betrachtlicher Aufwand zur Bestimmung der Pfeilerstarke gemacht wurde, wurde der anderen Halfte der Sicherheitsfaktorsgleichung nicht die gleiche Aufmerksamkeit gewidmet. Die auf die Pfeiler wirkende Last wurde immer unter Verwendung der Tributary Area Theory (TAT) berechnet. Diese Arbeit fast neuere Studien betreffend der Belastung von Kohlepfeilern unter Verwendung verschiedener numerischer Modelle zusammen. Die Schlussfolderung ist, daß obwohl unter bestimmten Vorraussetzungen bedeutende Unterschiede existieren, nach wie vor ein bezwingendes Argument besteht TAT in der Kohlepfeilerauslegung zu verwenden.


The traditional way of calculating pillar loads in South African coal mining, is using the Tributary Area Theory, TAT, which is based on the assumption that each pillar is responsible for bearing the weight of the overburden above it. While this is a handy and practical approach, originating at a time when numerical models were not yet in common use, the advent of micro computers and the development of numerical codes capable of calculating the loads more accurately, has raised questions about the continued application of the simplified model.

The prerequisites for using the TAT are not always adhered to in general mining practice. They are that the layout must be regular and that the panel width must be greater than the depth below surface. This places restrictions on the application of TAT, while its main advantage, ease of use, is no longer so great an advantage as before the advent of the micro computer.

By its nature, the TAT cannot take account of the load borne by inter panel pillars and other abutments. This means that it is reasonable to expect that it will over estimate pillar loads.

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