Page 384 - Rock Mechanics For Underground Mining

MINING METHODS AND METHOD SELECTION

Figure 12.13 Mining layout for
transverse sublevel caving (after
Hamrin, 2001).

12.4.8 Sublevel caving (Figure 12.13)
This mining method exploits a true caving technique, in that the aim of mining activity
is to induce free displacement of the country rock overlying an orebody. Operations
in the orebody are undertaken in headings developed at comparatively small vertical
intervals. Ore is fragmented using blast holes drilled upwards in fans from these
headings. Since the ore is blasted against the caved waste, explosive consumption in
blasting is high. This is due to the necessity to consolidate the caved waste as blasting
occurs in order to generate an expansion (swell) volume for the fragmenting ore. Ore
is extracted selectively, with a front-end loader operating in the drill heading, from the
local concentration of fragmented orebody rock contained within the caved waste. As
broken ore is extracted at the drawpoint, fragmented ore and enclosing caved waste
displace to fill the temporary void. The success of draw, and of the method itself, is
determined by the relative mobilities of caved waste and fragmented ore.
The main conceptual components of sublevel caving are indicated in Figure 12.13.
Mining progresses downwards in an orebody, with each sublevel being progressively
eliminated as mining proceeds. Headings serve as both drill drifts and transport open-
ings, in which ore is trammed to an ore pass located outside the orebody boundary.
Since the gravitational flow of the granular medium formed by the broken ore and
caved waste controls the ultimate yield from the orebody, generation of the caving
mass and the disposition of the drill headings are the important fundamental and prac-
tical aspects of the mining method. Figure 12.13 illustrates the transverse sublevel
caving mining method. A longitudinal sublevel caving method may also be used in
narrow orebodies.
Generally, sublevel caving is suitable only for steeply dipping orebodies, with
reasonably strong orebody rock enclosed by weaker overlying and wall rocks. The
ore must be of sufficient grade to accept dilution, perhaps exceeding 20%, arising
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