Page 398 - Rock Mechanics For Underground Mining
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PILLAR SUPPORTED MINING METHODS
Figure 13.10 Distribution of verti-
cal stress in a coal pillar at various
stages of pillar failure (after Wagner,
1980).
Galvin et al. (1999) have further developed the approach outlined in the preceding
paragraphs by adding more recent data for failed and unfailed pillars from Australian
andSouthAfricancoalminesandre-analysingthecombineddatabase.Theyalsomod-
ified the previous analysis to establish a new minimum critical pillar width for pillars
whose bases may be represented as parallelepipeds. With reference to Figure 13.11,
Galvin et al. (1999) re-wrote equation 13.7 as
w eo = o w (13.9)
where w is the minimum width of the pillar (i.e. w = w 1 sin
) and the dimensionless
parameter o is defined by
o = 2w 2 /(w 1 + w 2 ) (13.10)
The range taken by this parameter is 1 ≤ o < 2 as the plan aspect ratio of the pillar
ranges from unity towards infinity. Galvin et al. (1999) suggest that the effective width
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