Page 405 - Rock Mechanics For Underground Mining

DESIGN OF A STOPE-AND-PILLAR LAYOUT

Figure 13.16 Representation of a
partial extraction operation (a) in
terms of an equivalent volume, total
area extraction (b).

single-phase mining operation, the mechanical integrity of the pillar support is as-
sured, and volume extraction ratio is maximised. A graphical, heuristic procedure is
used to demonstrate how this objective may be realised.
Considering a representative element of a mine structure, shown in Figure 13.16a,
thevolume V e ofcoalextractedfromablockofplandimensionsw o + w p ,andworking
height h,is
2
2
V e = h[(w o + w p ) − w ] (13.19)
p
To obtain the same extraction volume V e by complete extraction over the area of the
2
element, i.e. over (w o + w p ) , a stope height h e , called the equivalent working height,
could be mined. This situation is illustrated in Figure 13.16b. The equivalent working
height is given by the expression
2
2
2
h e (w o + w p ) = V e = h[(w o + w p ) − w ]
p
or
2
h e = h[1 − (w p /(w o + w p )) ] (13.20)
The yield of a naturally supported operation can be measured conveniently in
terms of the equivalent working height, h e , of an associated, fictitious operation in
which extraction is complete over the area of a representative element of the deposit.
Thus, any change in stoping geometry which increases the equivalent working height
represents an increase in the yield performance of the operation. The effect of varying
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