Pillar loading part ii: model studies

The research work on pillar loading has been concerned with the combining of existing scientific theories into a rational hypothesis for predicting the loading of pillars. With the establishment of this hypothesis empirical substantiation or modification became required. The data from existing model work was analysed and supplementary experimental work conducted, so that the various parameters indicated by the hypothesis as being significant could be examined. Measurements of pillar stresses in laboratory models of gelatin, Araldite-type materials, mortar and steel showed that it is possible to predict the variation of pillar loadin.g with location within the mining zone, with variation of pillar height, with variation of pillar breadth, with the number of pillars across the mining zone, with the variation of the compressibility of the pillar ground with respect to that of the walls, with variation in the magnitude of the field stress component acting transversely to the mining zone or vein, and, above all, with the extraction ratio. However, by analysing data with respect to the various parameters it was found necessary to modify the theoretical equations for the functions including the location of the pillar, the effect of the stress component acting transversely to the mining zone, and the effect of pillar breadth in a mining zone having pillars of unequal width. These modifications have been made following the traditional engineering procedure of taking into account both the empirical evidence and the mechanism (if it can be recognized but has not been included in the theory) that is causing the deviation of the data from theory. The most significant parameters, aside from the extraction ratio, affecting the pillar loading have been shown to be the ratio of compressibility of the pillar rock to wall rock, the height of the pillar, and the breadth of the pillar in mines with pillars of unequal width,