Page 501 - Rock Mechanics For Underground Mining

PROBLEMS

Determine the width of pillar, w p , required if the roadway next to one panel is to
be outside the 10% zone of influence of the adjacent panel with respect to vertical
stresses.

4 An estimate of the dimensions of the flow and limit ellipsoids is required for use
in preparing a preliminary sublevel caving layout. The trial height of gravity flow
is to be h N = 16 m. Using Janelid and Kvapil’s approach with an eccentricity of
ε = 0.973, and assuming the loosening factor for the material in the limit ellipsoid
to be = 1.080, calculate predicted values of the major and minor semi-axes and
volumes of the flow and limit ellipsoids.
What values of ring burden and slice width do these results indicate are required
to minimise dilution and ore loss in sublevel caving operations?
5 A 60 m high block of caved ore under a capping of waste is to be drawn using
drawpoints spaced on 10 m centres. Field trials show that one drawpoint will pass the
material originally contained within the ellipsoid

2
6x + 0.5(y − 1.4 V 1/3 2 2/3
) = V
where x and y are measured horizontally and vertically from an origin on the centre-
line at the top of the drawpoint, and V is the volume drawn. The caved ore has a unit
weight of 25 kN m −3 and the loosening factor is = 1.066.
(a) Will the waste-ore contact be displaced by drawing 1000 tonnes of ore from one
drawpoint?
(b) How much ore can be drawn from one drawpoint before waste appears?

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