Geomechanics and Ground Control · Ground Control · 2 marks · Numerical answer
A square coal pillar has35 m centre-to-centre spacing and5 m galleries. It is split by5 m crosscuts into four equal square stooks. Height is3 m. With $S_p=S_1(0.64+0.36w/h)$,find percentage reduction in safety factor to two decimals.
The initial solid pillar is30 m wide. Each stook is (30−5)/2 =12.5 m wide. The original and split strength factors are4.24 and2.14, respectively. Remaining load-bearing area falls from900 to625 m², so tributary stress increases by900/625. Therefore the safety-factor ratio is (2.14/4.24) × (625/900) =0.35050. Its percentage reduction is64.95%.
