Double Square Chain Pillars

The only physical changes from a single line of square chain pillars is that the efffective width of the chain pillar support area becomes (2p + B) and the load is borne by two pillars of a plan area 2p2. The respective average pillar stresses for this situation are:

for w/h < 2tan f

for w/h >= 2tan 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)
B = bord (heading) width (m)

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