Engineering Rock Mechanics

388
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Strain
proportion

Ratio of
distance from
panel centre
to deDth 0.00 0.02 0.11 0.19 0.24 0.29 0.31 0.38 0.42 0.49 0.52 0.59 0.67 1.11

-0.70 -0.80 -1.00 -0.80 -0.40 0.00 0.40 0.80 1.00 0.80 0.60 0.40 0.20 0.00

In addition, the multipliers for the maximum contractile and ex-

tensile strains for these panel width to panel depth ratios are both

equal to about 0.7.

A20.6 Width of panel = 200 m, depth of panel = 250 m, seam thick-

ness = 3 m.

As the ratio of maximal subsidence to extraction thickness is about 0.75,

for an extraction thickness of 3 m the maximal subsidence - directly

above the centre of the panel - will be about 2.25 m. This figure is now

used to scale the dimensionless profile data taken from the SEH, in order

to produce the subsidence profile.

The subsidence profile data are converted into actual subsidence val-

ues by multiplying the values in the first row by 2.25 m (the magnitude

of the maximum subsidence) and actual distances by multiplying the

values in the second row by 250 m (the depth to the panel). This results

in the following:

Subsidence (m) 2.138 2.025 1.800 1.575 1.350 1.125 0.900 0.675 0.450 0.225 0.000

Distance (m) 20.0 25.0 42.5 50.0 62.5 72.5 80.0 95.0 105.0 155.0 277.5

These results can then be plotted, as shown in the following diagram.

Notice from this diagram that, above the panel edge, the subsidence is

greater than 0.5 m, and that the overall width of the subsidence trough is

more than 500 m.

distance from panel centre line, m

0 50 100 150 200 250 300

1 .oo

1.50

2.00

a

The transverse strain profile is produced in the same way as the

subsidence profile. The results are given in the table and diagram below.