Geomechanics and Ground Control · Ground Control · 2 marks · Numerical answer
A flat bord-and-pillar panel’s extraction ratio increases from 0.15 to 0.25 by widening galleries. Using tributary-area loading, find percentage change in pillar stress, to two decimals.
Average pillar stress is σv/(1−e). Thus final/initial stress = (1−0.15)/(1−0.25)=0.85/0.75=1.133333. The percentage increase is (1.133333−1)×100=13.33%. The change in extraction percentage points alone is not the stress increase.
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