Page 390 - Rock Mechanics For Underground Mining

PILLAR SUPPORTED MINING METHODS

Figure 13.3 Layout of barrier pillars
and panel pillars in a laterally exten-
sive orebody.

to their different functions. In the following discussion, attention is confined to the
performance and design of panel pillars, since their rˆole is that most frequently and
generally exploited in stoping practice.

13.2 Field observations of pillar performance

The most convenient observations of pillar response to induced mining loads and
displacements are made in room and pillar operations, since the method allows direct
access to the pillar sites. Detailed observation and measurement of pillar behaviour
have been reported by many researchers, including Bunting (1911), Greenwald et al.
(1939, 1941), Hedley and Grant (1972), Wagner (1974, 1980), Van Heerden (1975),
Hardy and Agapito (1977), and Hedley et al. (1984). Some particularly useful sum-
maries on pillar performance, analysis of their load-bearing capacity and pillar design
have been provided by Salamon and Munro (1967), Coates (1981) and Lunder and
Pakalnis (1997). For purposes of illustration, the initial discussion which follows is
concerned with pillars subject to nominal uniaxial loading. Subsequent discussion
takes account of more complex states of stress in pillars.
Stoping activity in an orebody causes stress redistribution and an increase in pillar
loading, illustrated conceptually in Figure 13.4. For states of stress in a pillar less
than the in situ rock mass strength, the pillar remains intact and responds elastically
to the increased state of stress. Mining interest is usually concentrated on the peak
load-bearing capacity of a pillar. Subsequent interest may then focus on the post-peak,
or ultimate load-displacement behaviour, of the pillar.
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