Page 102 - Rock Mechanics For Underground Mining

ROCK MASS STRUCTURE AND CHARACTERISATION

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borehole axis, and of the reference line, are 225 and 60 respectively, determine the
true orientation of the discontinuity.
8 Assume that, for the rock mass described in Problem 1, both sets of discontinuities
strike perpendicular to the drive axis. The intact rock material has a uniaxial com-
pressive strength of 120 MPa, the joint surfaces are slightly rough with an average
separation of 0.2 mm and, although there is water in the joints, the flow into the
excavation is quite small.
Determine the basic CSIR geomechanics classification for this rock mass (Ta-
ble 3.5). How does application of the adjustments for joint orientations for tunnelling
given by Tables 3.5 and 3.6 affect this classification?
Is the adjusted RMR value likely to provide a satisfactory guide to roof stability in
this case?

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