Pillar loading part iii: field measurements

Abstract

This work is in the area of engineering theory. It is concerned with the combining of existing scientific theories into a rational hypothesis for predicting the loading of pillars. Hitherto, this has only been possible in a very crude way and only for horizontal workings. Analytical work to predict pillar loadings for long mining zones in elastic ground results in equations which include, in the form of dimensionless parameters, the significant geometrical and material properties affecting pillar loading. Measurements of pillar stresses in laboratory models of gelatin, of Araldite-type materials, of mortar, and of steel show that it is possible to predict the variation of pillar loading--with location within the mining zonewith variation of pillar height--with variation in pillar breadthwith the number of pillars across the mining zone--with the variation of the compressibility of the pillar ground with respect to that of the wallswith variation in the magnitude of the field stress component acting transversely to the mining zone or vein,and, above all, with the extraction ratio. The results of pillar stress measurements in a lead mine, two iron mines, a coal mine and a uranium mine indicate that the most significant parameter causing deviation from the predicted pillar stresses is the variation in the relative compressibility of the pillar rock. The tributary area theory was found not to predict actual pillar loadings with an acceptable accuracy nor to account for changes in pillar loadings resulting from changes in the above factors included in the new hypothesis.