Rectangular chain pillars are employed extensively and frequently in preference to square pillars in view of less junctions being formed during development. The average pillar stress is given by:
for w/h < 2 tan f
for w/h >= 2 tan f
Where :
w = width of longwall face (m)
h = depth below surface (m)
g = average density of overburden (kg/m3)
f = average angle of shear (o)
p = pillar width (m)
L = pillar length (m)
B = bord (heading) width (m)
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