Pillar stability is one of important aspects for underground mines.Generally,the stability of the pillars is evaluated empirically based on case studies and site-specific rock mass conditions in mines.Nevertheless the empirical approach applicability can sometimes be constrained.The numerical-based approaches are potentially more useful as parametric studies can be undertaken and,if calibrated,can be more representative.Both empirical and numerical approaches are dependent on the strength evaluation of the pillars while the strain developing in the pillars is seldom taken into consideration.In this paper,gypsum and sandstone samples were tested in laboratory with different width-to-height ratios (W/H) to adapt the strain evaluation method to the laboratory-based pillars.A correlation was then developed between the strain and the width-to-height ratio for pillar monitoring purposes.Based on the results,a flowchart was created to conduct back analysis for the existing pillars to evaluate their stability and design new pillars,considering the strain analysis of the existing pillars with the W/H ratios modelled.
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