Abstract:
A number of shallow coal or hard rock mines employ pillar mining systems as a strategy for
roof failure control. In certain platinum mine layouts, pillars are designed to ‘crush’ in a stable
manner as they become loaded in the panel back area. The correct sizing of pillars demands
some knowledge of the pillar strength and the overall layout stress distribution. It is particularly
important to understand the impact of the layout geometry on the effective regional ‘stiffness’
of the rock mass around each pillar. An important design strategy is to model relatively detailed
layout configurations which include a precise representation of the local pillar layout geometry
and to analyse multiple mining scenarios and extraction sequences to select optimal pillar sizes
and barrier pillar spacing. Although computational solution techniques are now impressive in
terms of run time efficiency, a major difficulty is often encountered in assigning suitable material
properties to the pillars and in devising an effective material description of the layered rock strata
overlying the mine excavations. This paper outlines an efficient numerical strategy that can be
used to assess large-scale pillar layout performance while retaining the ability to modify individual
pillar constitutive behaviour. The proposed method is applied to selected layouts to compare
estimated average pillar stress values against values determined by detailed modelling and against
observed behaviour.
