Page 475 - Rock Mechanics For Underground Mining

SUBLEVEL CAVING

Figure 15.23 Vertical section width increases and as the extraction velocity increases. If it is assumed that the flow
through the longitudinal axis of an
may be described by equations 15.6 to 15.10, and that h N 2S where S is the slice
extraction drift, showing (a) ring
height, then the semi-width of flow, r, can be found from equation 15.10 as
burden, V , and slice gradient, , and
(b) truncated ellipsoid of motion.
2
r S[6(1 − ε )] 1/2 (15.11)
where ε is the unknown eccentricity, dependent on the height of flow and the particle
size distribution.
It must be recognised that the classical concept of gravity flow in sublevel caving
operationsoutlinedaboveisbasedonanumberofidealisationsandcannotbeexpected
to represent accurately all of the circumstances met in mining practice. Not only might
the flow and limit “ellipsoids” be more like inverted tear-drops than true ellipsoids,

Figure 15.24 Flow pattern in the
plane of the wall of a vertical slice.
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