Page 392 - Rock Mechanics For Underground Mining
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PILLAR SUPPORTED MINING METHODS
Figure 13.5 Principal modes of de- adjacent country rock. Yield of the soft layers generates transverse tractions over
formation behaviour of mine pillars. the pillar end surfaces and promotes internal axial splitting of the pillar. This may be
observed physically as lateral bulging or barrelling of the pillar surfaces. Geomechan-
ical conditions favouring this mode of response may occur in stratiform orebodies,
where soft bedding plane partings define the foot wall and hanging wall for the ore-
body. The failure condition is illustrated in Figure 13.5c.
Other specific modes of pillar response may be related directly to the structural
geology of the pillar. For example, a pillar with a set of natural transgressive fractures,
as illustrated in Figure 13.5d, can be expected to yield if the angle of inclination of
the fractures to the pillar principal plane (that perpendicular to the pillar axis) exceeds
their effective angle of friction. The amount of slip on the fractures required for yield,
Figure 13.6 Schematic illustration
of the evolution of fracture and fail-
ure in a pillar in massive rock (after
Lunder and Pakalnis, 1997).
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